Professor Stephen Sweeney


Visiting Professor of Physics
PhD, BSc, CertEd, FInstP, CPhys, FSPIE

About

Areas of specialism

Photonics; Semiconductor Physics; Semiconductor Materials; Semiconductor Devices; Laser Physics

My qualifications

1995
BSc Applied Physics
University of Bath
1995
CertEd (Education)
University of Bath
1999
PhD Semiconductor Laser Physics
University of Surrey

Previous roles

2015 - 2018
Head of Department of Physics
Department of Physics, University of Surrey
2010 - 2015
Head of Photonics group
Advanced Technology Institute, University of Surrey
2009 - 2015
EPSRC Leadership Fellow
Engineering and Physical Sciences Research Council
01 January 2015 - 31 December 2015
President of the Physics and Astronomy Section
British Science Association

Affiliations and memberships

Institute of Physics
Fellow
Chartered Physicist
Institute of Electrical and Electronic Engineers
Senior Member
SPIE
Fellow

Research

Research interests

Publications

Mozhgan Yavari, Xueping Liu, Thomas Webb, K D G Imalka Jayawardena, Yuren Xiang, Stefanie Kern, Steven Hinder, Thomas J Macdonald, S Ravi P Silva, Stephen J Sweeney, Wei Zhang (2021)A synergistic Cs2CO3ETL treatment to incorporate Cs cation into perovskite solar cells: Via two-step scalable fabrication, In: Journal of Materials Chemistry C Materials for optical and electronic devices9(12)pp. 4367-4377 Royal Society of Chemistry

Triple cation CsFAMA perovskite films fabricated via a one-step method have recently gained attention as an outstanding light-harvesting layer for photovoltaic devices. However, questions remain over the suitability of one-step processes for the production of large-area films, owing to difficulties in controlling the crystallinity, in particular, scaling of the frequently used anti-solvent washing step. This can be mitigated through the use of the two-step method which has recently been used to produce large-area films via techniques such as slot dye coating, spray coating or printing techniques. Nevertheless, the poor solubility of Cs containing salts in IPA solutions has posed a challenge for forming triple cation perovskite films using the two-step method. In this study, we tackle this challenge through fabricating perovskite films on a caesium carbonate (Cs2CO3) precursor layer, enabling Cs incorporation within the film. Synergistically, we find that Cs2CO3 passivates the SnO2 electron transport layer (ETL) through interactions with Sn 3d orbitals, thereby promoting a reduction in trap states. Devices prepared with Cs2CO3 treatment also exhibited an improvement in the power conversion efficiency (PCE) from 19.73% in a control device to 20.96% (AM 1.5G, 100 mW cm−2) in the champion device. The Cs2CO3 treated devices (CsFAMA) showed improved stability, with un-encapsulated devices retaining nearly 80% efficiency after 20 days in ambient air.

Rémi Waché, Tim Fielder, Will E.C. Dickinson, Joe L. Hall, Peter Adlington, Stephen J. Sweeney, Steven K. Clowes (2020)Selective light transmission as a leading innovation for solar swimming pool covers, In: Solar Energy207pp. 388-397 Elsevier

An innovative, extrudable material with the ability to filter the sun’s energy has been developed for the mass manufacture of high performance swimming pool covers. Solar radiation in the visible spectrum ( nm) is absorbed by the material so that minimal visible light enters the pool water which inhibits photosynthesis to prevent algae growth. Furthermore, the material has high transmission properties in the near infrared that can be efficiently absorbed by the water allowing for a higher temperature increase compared to a standard non-selective opaque cover. We have developed a model to enable the cover efficiency to convert solar energy to heat a swimming pool, calculated based on the wavelength dependent absorption and transmission properties of the cover. We have validated this model using dedicated full-scale test-facility. Our results demonstrate that a selective transmission cover can increase the absolute heating efficiencies by approximately 12% compared to the fully opaque equivalent.

THOMAS WEBB, STEPHEN SWEENEY, WEI ZHANG (2021)Device Architecture Engineering: Progress toward Next Generation Perovskite Solar Cells, In: Advanced functional materials.

Over the past decade perovskite solar cells (PSCs) have quickly established themselves as a promising technology boasting both high efficiency and low processing costs. The rapid development and success of PSCs is a product of substantial research effort addressing compositional engineering, thin film fabrication, surface passivation and interfacial treatments. Recently, engineering of the device architecture has entered a renaissance with the emergence of several new bulk and graded heterojunction structures. These structures promote a lateral approach to the development of single-junction PSCs affording new opportunities in light management, defect passivation, carrier extraction and long-term stability. Following a short overview of the historic evolution of PSC architectures, we offer a detailed discussion of the promising progress of the recently reported perovskite bulk heterojunction (BHJ) and graded heterojunction (GHJ) approaches. To enable better understanding of these novel architectures, a range of approaches to characterizing the 2 architectures are presented. Finally, an outlook and perspective are provided offering insights into the future development of PSC architecture engineering.

Christopher R. Fitch, Dominic A. Duffy, Peter Ludewig, Wolfgang Stolz, Stephen J. Sweeney (2022)Refractive index dispersion of BGa(As)P alloys in the near-infrared for III-V laser integration on silicon, In: Journal of Applied Physics131(13) American Institute of Physics

BxGa(1−x)P and BxGa(1−x)AsyP(1−y) alloys are of potential interest in III-V heterostructures for integration with silicon. Waveguide design utilizing these alloys requires an understanding of the refractive index properties and their variation with composition. Refractive index dispersion was measured and modeled in the wavelength range of 827–2254 nm using spectroscopic ellipsometry at room temperature for samples with boron and arsenic fractions from 0% to 6.6% and 0% to 17%, respectively. The refractive index was found to increase with increasing boron composition as a result of strain due to lattice constant mismatch with the silicon substrate. For the arsenic-containing alloy, the refractive index was found to increase independently of strain. An empirical model based on the composition dependent variation of Cauchy dispersion function coefficients was developed for BGaAsP alloys lattice matched to silicon at the growth temperature. This model can be used to calculate the wavelength dependent refractive index of lattice matched boron and arsenic combinations for applications in semiconductor waveguides, an example of which is proposed. The results of this study are of interest more broadly for other III-V on silicon applications including photovoltaics and more generally in terms of the ellipsometric investigations of thin films on non-native substrates.

THOMAS WEBB, Xueping Liu, Robert J. E. Westbrook, Stefanie Kern, Muhammad T. Sajjad, Sandra Jenatsch, K. D. G. Imalka Jayawardena, Withanage Hashini Kawshika Perera, Igor Marko, Sanjayan Sathasivam, Bowei Li, MOZHGAN YAVARI, David J. Scurr, Morgan R. Alexander, Thomas J Macdonald, Saif A. Haque, Stephen Sweeney, Wei Zhang (2022)A Multifaceted Ferrocene Interlayer for Highly Stable and Efficient Lithium Doped Spiro-OMeTAD-based Perovskite Solar Cells, In: Advanced energy materials12(26)2200666 Wiley

Over the last decade, 2,2 '',7,7 ''-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9 '-spirobifluorene (spiro-OMeTAD) has remained the hole transporting layer (HTL) of choice for producing high efficiency perovskite solar cells (PSCs). However, PSCs incorporating spiro-OMeTAD suffer significantly from dopant induced instability and non-ideal band alignments. Herein, a new approach is presented for tackling these issues using the functionality of organometallocenes to bind to Li+ dopant ions, rendering them immobile and reducing their impact on the degradation of PSCs. Consequently, significant improvements are observed in device stability under elevated temperature and humidity, conditions in which ion migration occurs most readily. Remarkably, PSCs prepared with ferrocene retain 70% of the initial power conversion efficiency (PCE) after a period of 1250 h as compared to only 8% in the control. Synergistically, it is also identified that ferrocene improves the hole extraction yield at the HTL interface and reduces interfacial recombination enabling PCEs to reach 23.45%. This work offers a pathway for producing highly efficient spiro-OMeTAD devices with conventional dopants via addressing the key challenge of dopant induced instability in leading PSCs.

Bowei Li, Jun Deng, Joel A. Smith, Pietro Caprioglio, Kangyu Ji, Deying Luo, James D. McGettrick, K. D. G. Imalka Jayawardena, Rachel Kilbride, AOBO REN, Stephen Sweeney, Steven John Hinder, Jinxin Bi, S Ravi Pradip Silva, Wei Zhang, THOMAS WEBB, Igor Marko, Xueping Liu, YUREN XIANG, Joshua Dean Reding, HUI LI, Shixuan Du, D. G. Lidzey, Samuel D. Stranks, Trystan M. Watson, H. J. Snaith (2022)Suppressing Interfacial Recombination with a Strong-Interaction Surface Modulator for Efficient Inverted Perovskite Solar Cells, In: Advanced energy materials Wiley

Successful manipulation of halide perovskite surfaces is typically achieved via the interactions between modulators and perovskites. Herein, it is demonstrated that a strong-interaction surface modulator is beneficial to reduce interfacial recombination losses in inverted (p-i-n) perovskite solar cells (IPSCs). Two organic ammonium salts are investigated, consisting of 4-hydroxyphenethylammonium iodide and 2-thiopheneethylammonium iodide (2-TEAI). Without thermal annealing, these two modulators can recover the photoluminescence quantum yield of the neat perovskite film in contact with fullerene electron transport layer (ETL). Compared to the hydroxyl-functionalized phenethylammonium moiety, the thienylammonium facilitates the formation of a quasi-2D structure onto the perovskite. Density functional theory and quasi-Fermi level splitting calculations reveal that the 2-TEAI has a stronger interaction with the perovskite surface, contributing to more suppressed non-radiative recombination at the perovskite/ETL interface and improved open-circuit voltage (V-OC) of the fabricated IPSCs. As a result, the V-OC increases from 1.11 to 1.20 V (based on a perovskite bandgap of 1.63 eV), yielding a power conversion efficiency (PCE) from approximate to 20% to 21.9% (stabilized PCE of 21.3%, the highest reported PCEs for IPSCs employing poly[N,N ''-bis(4-butylphenyl)-N,N ''-bis(phenyl)benzidine] as the hole transport layer, alongside the enhanced operational and shelf-life stability for unencapsulated devices.

Thomas Webb, Stephen J. Sweeney, Wei Zhang (2021)Device Architecture Engineering: Progress toward Next Generation Perovskite Solar Cells, In: Advanced functional materials31(35)2103121pp. 2103121-n/a

Over the past decade, perovskite solar cells (PSCs) have quickly established themselves as a promising technology boasting both high efficiency and low processing costs. The rapid development and success of PSCs is a product of substantial research effort addressing compositional engineering, thin film fabrication, surface passivation, and interfacial treatments. Recently, engineering of device architecture has entered a renaissance with the emergence of several new bulk and graded heterojunction structures. These structures promote a lateral approach to the development of single‐junction PSCs affording new opportunities in light management, defect passivation, carrier extraction, and long‐term stability. Following a short overview of the historic evolution of PSC architectures, a detailed discussion of the promising progress of the recently reported perovskite bulk heterojunction and graded heterojunction approaches are offered. To enable better understanding of these novel architectures, a range of approaches to characterizing the architectures are presented. Finally, an outlook and perspective are provided offering insights into the future development of PSC architecture engineering. Four emerging perovskite structures that have origins in pre‐existing technologies such as silicon and chalcogenide‐based photovoltaic cells are reviewed. The implementation of the new architectures holds great promise in reducing transport losses, light management, and stability. To guide further research into these areas key design criteria are identified and key characterization methods discussed.

Dominic A Duffy, Igor P Marko, Christian Fuchs, Thilo Hepp, Jannik Lehr, Kerstin Volz, Wolfgang Stolz, Stephen J Sweeney (2022)Reduced Temperature-Dependence of Optical Gain in Type-II GaAs-based “W”-Laser Structures, In: The Institute of Electrical and Electronics Engineers, Inc. (IEEE) Conference Proceedings The Institute of Electrical and Electronics Engineers, Inc. (IEEE)

Conference Title: 2022 28th International Semiconductor Laser Conference (ISLC) Conference Start Date: 2022, Oct. 16 Conference End Date: 2022, Oct. 19 Conference Location: Matsue, JapanWe investigate the temperature-dependence of modal gain for type-II (GaIn)As/Ga(AsSb) “W”-laser structures operating around the O-band. Measurements show their potential to control the temperature dependence of the gain due to carrier-induced band bending effects. This is of interest to semiconductor laser and optical amplifier applications.

Christopher R. Fitch, Graham W. Read, Igor P. Marko, Dominic A. Duffy, Laurent Cerutti, Jean-Baptiste Rodriguez, Eric Tournie, Stephen J. Sweeney (2021)Carrier recombination and temperature-dependence of GaInSb quantum well lasers for silicon photonics applications, In: 2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)pp. 1-1 IEEE

Epitaxially grown III-V semiconductor lasers on silicon substrates are key to the development of low-cost silicon photonic circuits. Antimony based Composite Quantum Well (CQW) devices on silicon, which overcome lattice constant and thermal mismatch differences, have been successfully demonstrated in the important 1.55 m long-haul telecoms wavelength region [1] . However, further development is required to address high threshold current densities and temperature sensitivity. To improve these on-silicon devices we investigate and report on the efficiency limiting mechanisms of the equivalent active regions grown on GaSb. The devices investigated here consist of compressively strained Ga 0.8 In 0.2 Sb QWs with Al 0.35 Ga 0.65 As 0.03 Sb 0.97 barriers and Al 0.9 Ga 0.1 As 0.07 Sb 0.93 cladding layers lattice matched to a GaSb substrate [2] . In this paper we report on the temperature and high hydrostatic pressure dependent investigation of these devices. We identify details of the principal efficiency limiting mechanisms and sources of temperature sensitivity and provide specific recommendations for design improvement.

Dominic A. Duffy, Igor P. Marko, Christian Fuchs, Timothy D. Eales, Jannik Lehr, Wolfgang Stolz, Stephen J. Sweeney (2021)Injection- and Temperature-Dependence of Type-II 1.2-1.3 μm (GaIn)As/Ga(AsSb) "W"-Lasers, In: 2021 27th International Semiconductor Laser Conference (ISLC)pp. 1-2 IEEE

Type-II (GaIn)As/Ga(AsSb) "W"-lasers offer the possibility to develop efficient and thermally stable near-infrared lasers. In this work, we investigate the temperature- and injection-dependent properties of "W"-lasers operating between 1200-1260 nm and use this to quantify the influence of radiative and non-radiative recombination on device performance.

C. R. Fitch, G. W. Read, I. P. Marko, D. A. Duffy, Laurent Cerutti, Jean-Baptiste Rodriguez, Eric Tournié, Stephen J. Sweeney (2021)Carrier recombination and temperature-dependence of GaInSb quantum well lasers for silicon photonics applications
N.F. Masse, I.P. Marko, S.J. Sweeney, A.R. Adams, N. Hatori, M. Sugarawa (2005)The influence of p-doping on the temperature sensitivity of 1.3 /spl mu/m quantum dot lasers, In: 2005 IEEE LEOS Annual Meeting Conference Proceedingspp. 604-605 IEEE

We find that non-radiative recombination plays an important role in p-doped quantum-dot lasers. Along with carrier thermalisation effects, this is responsible for the temperature insensitive operation as observed around room temperature in these lasers.

K. Hild, S.J. Sweeney, D.A. Lock, S. Wright, J.-B. Wang, S.R. Johnson, Y.-H. Zhang (2005)On the thermal stability of 1.3 /spl mu/m GaAsSb/GaAs-based lasers, In: 2005 IEEE LEOS Annual Meeting Conference Proceedingspp. 331-332 IEEE

In spite of the almost ideal variation of the radiative current of 1.3 mum GaAsSb/GaAs-based lasers, the threshold current, J th , is high due to non-radiative recombination accounting for 90% J th near room temperature. This also gives rise to low T 0 values ~60 K close to room temperature, similar to that for InGaAsP/InP

Zoe L. Bushell, Christopher A. Broderick, Lukas Nattermann, Rita Joseph, Joseph L. Keddie, Judy M. Rorison, Kerstin Volz, Stephen J. Sweeney (2020)Giant Bowing of the Bandgap and Spin-Orbit Splitting in GaP1-xBix Dilute Bismide Alloys, In: 2020 22nd International Conference on Transparent Optical Networks (ICTON)pp. 1-1 IEEE

Highly-mismatched III-V semiconductor alloys containing dilute concentrations of bismuth (Bi) have attracted significant attention in recent years since their unique electronic properties open up a range of possibilities for practical applications in semiconductor lasers, photovoltaics, spintronics, photodiodes, and thermoelectrics. Research on dilute bismide alloys has primarily focused to date on \text{GaAs}_{1-x}\text{Bi}_{x} , where incorporation of Bi brings about a strong reduction of the direct \Gamma -point band gap ( E_{g}{}^{\Gamma} ) -by up to 90 meV per % Bi at low Bi compositions x -characterised by strong, composition-dependent bowing. This unusual behaviour derives from the large differences in size (covalent radius) and chemical properties (electronegativity) between As and Bi.Bi, being significantly larger and more electropositive than As, acts as an isovalent impurity which primarily impacts and strongly perturbs the valence band (VB) structure. This is in contrast to dilute nitride alloys, in which small electronegative nitrogen (N) atoms strongly perturb the conduction band (CB) structure in \text{GaN}_{x}\text{As}_{1-x} and related alloys. Additionally, Bi, being the largest stable group-V element, has strong relativistic (spin-orbit coupling) effects. As such, the reduction of E_{g}{}^{\Gamma} in (\text{In})\text{GaAs}_{1-x}\text{Bi}_{x} is accompanied by a strong increase in the VB spin-orbit splitting energy ( \Delta_{\text{SO}} ).

Xueping Liu, THOMAS WEBB, Linjie Dai, Kangyu Ji, Joel A. Smith, Rachel Kilbride, MOZHGAN YAVARI, Jinxin Bi, AOBO REN, Yuanyuan Huang, Zhuo Wang, Yonglong Shen, Guosheng Shao, Stephen Sweeney, Steven John Hinder, HUI LI, D. G. Lidzey, Samuel D. Stranks, Neil C Greenham, Wei Zhang, S Ravi Pradip Silva (2022)Influence of halide choice on formation of low‐dimensional perovskite interlayer in efficient perovskite solar cells Wiley

Recent advances in heterojunction and interfacial engineering of perovskite solar cells (PSCs) have enabled great progress in developing highly efficient and stable devices. Nevertheless, the effect of halide choice on the formation mechanism, crystallography and photoelectric properties of the low-dimensional phase still requires further detailed study. In this work, we present key insights into the significance of halide choice when designing passivation strategies comprising large organic spacer salts, clarifying the effect of anions on the formation of quasi2D/3D heterojunctions. To demonstrate the importance of halide influences, we employ novel neo-pentylammonium halide salts with different halide anions (neoPAX, X = I, Br or Cl). We find that regardless of halide selection, iodide-based (neoPA)2(FA)(n-1)PbnI(3n+1) phases are formed above the perovskite substrate, while the added halide anions diffuse and passivate the perovskite bulk. In addition, we also find the halide choice has an influence on the degree of dimensionality (n). Comparing the three halides, we find that chloride-based salts exhibit superior crystallographic, enhanced carrier transport and extraction compared to the iodide and bromide analogs. As a result, we report high power conversion efficiency in quasi-2D/3D PSCs, which are optimal when using chloride salts, reaching up to 23.35% and improving long-term stability.

S. J. Sweeney, I. P. Marko, S. R. Jin, K. Hild, Z. Batool (2015)Bismuth-based semiconductors for mid-infrared photonic devices, In: 2015 IEEE Summer Topicals Meeting Series (SUM)pp. 181-182 IEEE

Owing to the versatile band-structure made possible through the introduction of bismuth in III-V systems, we discuss the potential to produce efficient emitters and detectors in the mid-infrared based upon conventional GaAs and InP substrates.

Christopher A. Broderick, Judy M. Rorison, Igor P. Marko, Stephen J. Sweeney, Eoin P. O'Reilly (2016)GaAs-based dilute bismide semiconductor lasers: Theory vs. experiment, In: 2016 International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD)pp. 209-210 IEEE

We present a theoretical analysis of the electronic and optical properties of near-infrared dilute bismide quantum well (QW) lasers grown on GaAs substrates. Our theoretical model is based upon a 12-band k·p Hamiltonian which explicitly incorporates the strong Bi-induced modifications of the band structure in pseudomorphically strained GaBi x As 1-x alloys. We outline the impact of Bi on the gain characteristics of ideal GaBi x As 1-x /(Al)GaAs devices, compare the results of our theoretical calculations to experimental measurements of the spontaneous emission (SE) and optical gain - a first for this emerging material system - and demonstrate quantitative agreement between theory and experiment. Through our theoretical analysis we further demonstrate that this novel class of III-V semiconductor alloys has strong potential for the development of highly efficient GaAs-based semiconductor lasers which promise to deliver uncooled operation at 1.55 μm.

SJ Sweeney, A Jha (2015)Preface, In: Journal of Physics: Conference Series619(1)
SJ Sweeney (2010)Bismide-alloys for higher efficiency infrared semiconductor lasers, In: 22nd IEEE International Semiconductor Laser Conferencepp. 111-112

The incorporation of Bismuth in III-V alloys, such as GaAsBi/GaAs provides a preferential semiconductor band structure to suppress non-radiative recombination and optical losses, improving the efficiency and temperature stability of infrared semiconductor lasers.

SJ Sweeney, IP Marko, SR Jin, K Hild, Z Batool, P Ludewig, L Natterman, Z Bushell, W Stolz, K Volz, CA Broderick, M Usman, PE Harnedy, EP Oreilly, R Butkute, V Pacebutas, A Geiutis, A Krotkus (2014)Electrically injected GaAsBi quantum well lasers, In: Conference Digest - IEEE International Semiconductor Laser Conferencepp. 80-81 IEEE

GaAsBi QWs have the potential to remove inherent recombination losses thereby increasing the efficiency and reducing the temperature sensitivity of near-infrared telecommunications lasers. GaAsBi QW lasers are reported and prospects for 1550nm operation are discussed.

IP Marko, SJ Sweeney (2015)Optical and electronic processes in semiconductor materials for device applications, In: Springer Series in Materials Science203pp. 253-297 Springer

In this chapter we consider the important optical and electronic processes which influence the properties of semiconductor photonic devices. Focussing on a number of material systems, we describe semiconductor materials and structures used for light-emitting applications (lasers and LEDs) operating in a wide spectral range from visible to mid-infrared. The main carrier recombination mechanisms in semiconductor devices are discussed and experimental methodologies for measuring and analysing these mechanisms are introduced. Near infra-red (IR) quantum well (QW) lasers are discussed in depth considering several new approaches to overcome fundamental performance issues. Different approaches for the longer wavelength (mid-IR) semiconductor devices are reviewed showing the benefits of different approaches to material and device design where energy efficiency and high temperature operation are the principal concerns. Finally, semiconductor lasers and LEDs for the visible spectral range are briefly introduced in terms of the most important issues related to their performance.

R Fehse, EP O'Reilly, SJ Sweeney, AR Adams, D McConville, H Riechert, L Geelhaar (2005)Investigation of carrier recombination processes and transport properties in GaInAsN/GaAs quantum wells, In: AIP Conference Proceedings772pp. 985-986 American Institute of Physics

It is shown that the dramatic changes in threshold current density with changing active region growth temperature in 1.3μm GaInNAs-based lasers can be attributed almost entirely to changes in the defect related monomolecular recombination current in the optically active material. In addition, growth temperature dependent changes in the QW morphology are shown to have a significant influence on the transport properties of the structure. © 2005 American Institute of Physics.

BG Crutchley, Igor Marko, Alfred Adams, Stephen Sweeney (2013)Investigating the efficiency limitations of GaN-based emitters, In: 2013 Conference on Lasers and Electro-Optics Europe and International Quantum Electronics Conference, CLEO/Europe-IQEC 2013

In this study low temperature and high pressure techniques have been used to investigate the recombination processes taking place in InGaN-based quantum well light emitting diodes (LEDs) which have emission across the blue-green region. Despite relatively high peak efficiencies of the GaN-based emitters, there remain issues relating to the strong efficiency reduction at higher currents that are required for normal operation in most applications. It is observed that there is a relative reduction in efficiency as injection current is increased in a phenonmenon which is known as efficiency droop. There are three main arguments for the cause of efficiency droop that are discussed in the literature: non-radiative Auger recombination, carrier leakage and a defect-related loss mechanism. In spite of extensive research to date, there is little agreement on the cause of efficiency droop as most experiments can only measure the overall efficiency behaviour leading to difficulties in determining the individual contributions from the different loss mechanisms. © 2013 IEEE.

IP Marko, AM Aldukhayel, AR Adams, SJ Sweeney, R Teissier, AN Baranov, S Tomić (2010)Physical properties of short wavelength 2.6μm InAs/AlSb-based quantum cascade lasers, In: Conference Digest - IEEE International Semiconductor Laser Conferencepp. 95-96 IEEE

We used high hydrostatic pressure techniques to understand the deteriorating temperature performance with decreasing wavelength of short wavelength quantum cascade lasers. Influence of inter-valley scattering and distribution of the electron wave functions will be discussed.

R Maspero, SJ Sweeney, M Florescu (2013)Modelling the Auger Recombination rates of GaAs(1-x)Bi x alloys, In: 13th International Conference on Numerical Simulation of Optoelectronic Devices, NUSOD 2013pp. 81-82

We calculate the Conduction, Heavy Hole (HH) - Split-off Hole (SO), HH (CHSH) Auger Recombination rates for GaAs(1-x)Bix alloys, which are candidates for highly efficient telecommunication devices. A ten-band, tight-binding method, including spin-orbit coupling, was performed on a 9×9×9 strained supercell in order to generate an accurate band structure to perform the calculation on. This band structure was then unfolded to give a true E-k relation. As predicted by experiment, there should be a decrease in the Auger recombination rate as the concentration of Bismuth increases ending in a suppression at greater than ∼11% Bismuth. © 2013 IEEE.

Stephen John Sweeney, Weijun Fan, Boon S. Ooi, Dao Hua Zhang (2020)Virtual Special Issue Dedicated to the 10th International Conference on Materials for Advanced Technologies (ICMAT), Symposium C: Semiconductor Photonics, In: IEEE journal of quantum electronics56(2)8994816pp. 1-3 IEEE

This Special Issue is associated with the 10th International Conference on Materials for Advanced Technologies (ICMAT), Symposium C: Semiconductor Photonics held on 23-28 June, 2019 at Marina Bay Sands in Singapore. Organised through the Materials Research Society of Singapore (MRS-S), ICMAT has been held since 2001 and has attracted strong interest amongst the global materials science and engineering research communities. The 10 th conference in the ICMAT series attracted over 3,500 delegates with a number of keynote and plenary presentations notably including four Nobel Laureates in Physics and Chemistry. The ICMAT conference consists of a number of topical symposia. Symposium C was organized jointly with Australian MRS and co-chaired by Professors Dao-Hua Zhang (NTU, Singapore), Chennupati Jagadish (ANU, Australia), Stephen J. Sweeney (University of Surrey, UK), Boon S. Ooi (KAUST, Saudi Arabia), Hao Gong (NUS, Singapore) and Weijun Fan (NTU, Singapore). The Symposium focused on recent developments in materials for applications in photonic devices covering systems including III-V and II-VI semiconductors, group IV alloys for silicon compatibility, oxides and perovskites for solar cell and emitter applications, quantum dot based devices and in general a wide variety of organic and inorganic materials spanning applications from the ultra-violet through to the mid-infrared. In total, 20 invited and 53 oral and 19 poster papers were presented over the four days of technical sessions.

C. Termsuk, S. J. Sweeney, C. Shenton-Taylor (2022)Thermoluminescence glow curve study of beta irradiated germanium doped core fibre with different dopant concentrations, In: Radiation physics and chemistry (Oxford, England : 1993)193109974 Elsevier

This paper reports the assessment of commercial Ge-doped fibres as a potential dosimeter. The thermoluminescence response was measured for 4 fibre types: commercial multi-mode germanium doped core fibres at 4% and 6% weight Ge doping; single mode fibre with a 17% Ge and 1% B (GeB) doped core; and undoped silica fibre. The fibres were subjected to beta irradiation (Sr-90/Y-90), heated from room temperature to 400 degrees C. The 6% Ge doped fibre exhibited sensitivity of 7.7 +/- 0.2 counts.mm(-1).Gy(-1).mu m(-2), greater than the 4% Ge-doped and GeB fibres by factors of 9.2 and 1.3 respectively. All the core-doped fibres (Ge, GeB) showed a high linear response across the dose range 1-10 Gy (R-2 = 0.99). Increasing the Ge concentration from 4 to 17% lowered the temperature of the glow curve peak from 317 degrees C to 248 degrees C. The glow curve for both Ge doped core fibres were analysed using a computerised glow curve deconvolution (CGCD) in TolAnal software. When including Ge dopants, the estimated trap depth for five sub-peaks in the Ge doped fibre was reported between 0.6 and 1.54 eV.

Zoe C. M. Davidson, Judy M. Rorison, Stephen J. Sweeney, Christopher A. Broderick (2021)Strain-balanced GaAs1-xBix/GaNyAs1-y W-type quantum wells for GaAs-based 1.3-1.6 mu m lasers, In: 2021 INTERNATIONAL CONFERENCE ON NUMERICAL SIMULATION OF OPTOELECTRONIC DEVICES (NUSOD)pp. 5-6 IEEE

Highly-mismatched alloys constitute a promising approach to extend the operational range of GaAs-based quantum well (QW) lasers to telecom wavelengths. This is challenging using type-I QWs due to the difficulty to incorporate sufficient N or Bi via epitaxial growth. To overcome this, we investigate a novel class of strain-compensated type-II QWs combining electron-confining, tensile strained GaNyAs1-y and hole-confining, compressively strained GaAs1-xBix layers. We systematically analyse the optoelectronic properties of W-type GaAs1-xBix/GaNyAs1-y QWs, and identify paths to optimise their threshold characteristics. Solving the multi-band k.p Schrodinger equation self-consistently with Poisson's equation highlights the importance of electrostatic confinement in determining the optical and differential gain of these QWs. Our calculations demonstrate that GaAs1-xBix/GaNyAs1-y QWs offer broad scope for band structure engineering, withW-type structures presenting the possibility to combine high long-wavelength gain with the intrinsically low non-radiative Auger recombination rates of type-II QWs.

Zoe C. M. Davidson, Thilo Hepp, Judy M. Rorison, Stephen J. Sweeney, Kerstin Volz, Christopher A. Broderick (2021)Type-II GaAs1-xBix/GaNyAs(1-y) "W" quantum wells for strain-compensated GaAs-based telecom lasers, In: 27TH INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE (ISLC 2021) IEEE

We discuss a new class of type-II quantum wells (QWs) that exploit the impact of Bi and N on the GaAs band-structure. Via growth, experiment, and theoretical calculations we highlight the properties of GaAs1-xBix/GaNyAs1-y "W" QWs, demonstrating a potential pathway to uncooled telecom-wavelength laser operation.

Aidas Baltusis, George Koutsourakis, Sebastian Wood, Stephen J. Sweeney (2021)Spatial Imaging of Minority Charge Carrier Lifetimes of Semiconductors using Digital Light Processing and Compressed Sensing, In: 2021 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO)pp. 1-2 IEEE

We propose and investigate a novel, rapid method for contactless spatial imaging of minority charge carrier lifetimes based on compressed sensing. The proposed method demonstrates an order of magnitude potential increase in imaging speeds. (C) 2021 The Author(s)

Timothy D Eales, Igor P Marko, Alfred R Adams, Jerry R Meyer, Igor Vurgaftman, Stephen J Sweeney (2021)Quantifying Auger recombination coefficients in type-I mid-infrared InGaAsSb quantum well lasers, In: Journal of physics. D, Applied physics54(5)055105 IOP Publishing

From a systematic study of the threshold current density as a function of temperature and hydrostatic pressure, in conjunction with theoretical analysis of the gain and threshold carrier density, we have determined the wavelength dependence of the Auger recombination coefficients in InGaAsSb/GaSb quantum well lasers emitting in the 1.7-3.2 µm wavelength range. From hydrostatic pressure measurements, the non-radiative component of threshold currents for individual lasers was determined continuously as a function of wavelength. The results are analysed to determine the Auger coefficients quantitatively. This procedure involves calculating the threshold carrier density based on device properties, optical losses, and estimated Auger contribution to the total threshold current density. We observe a minimum in the Auger rate around 2.1 µm. A strong increase with decreasing mid-infrared wavelength (

Dominic A. Duffy, Igor P. Marko, Christian Fuchs, Timothy D. Eales, Jannik Lehr, Wolfgang Stolz, Stephen J. Sweeney (2021)Performance characteristics of low threshold current 1.25 mu m type-II GaInAs/GaAsSb 'W'-lasers for optical communications, In: Journal of physics. D, Applied physics54(36)365104 Iop Publishing Ltd

Type-II 'W'-lasers have made an important contribution to the development of mid-infrared laser diodes. In this paper, we show that a similar approach can yield high performance lasers in the optical communications wavelength range. (GaIn)As/Ga(AsSb) type-II 'W' structures emitting at 1255 nm have been realised on a GaAs substrate and exhibit low room temperature threshold current densities of 200-300 A cm(-2), pulsed output powers exceeding 1 W for 100 mu m wide stripes, and a characteristic temperature T (0) approximate to 90 K around room temperature. Optical gain studies indicate a high modal gain around 15-23 cm(-1) at 200-300 A cm(-2) and low optical losses of 8 +/- 3 cm(-1). Analysis of the spontaneous emission indicates that at room temperature, up to 24% of the threshold current is due to radiative recombination, with the remaining current due to other thermally activated non-radiative processes. The observed decrease in differential quantum efficiency with increasing temperature suggests that this is primarily due to a carrier leakage process. The impact of these processes is discussed in terms of the potential for further device optimisation. Our results present strong figures of merit for near-infrared type-II laser diodes and indicate significant potential for their applications in optical communications.

Leh Woon Lim, Pallavi Patil, Igor P Marko, Edmund Clarke, Stephen J Sweeney, Jo Shien Ng, John P R David, Chee Hing Tan (2020)Electrical and optical characterisation of low temperature grown InGaAs for photodiode applications, In: Semiconductor science and technology35(9)095031 IOP Publishing

Dilute bismide and nitride alloys are promising semiconductors for bandgap engineering, opening additional design freedom for devices such as infrared photodiodes. Low growth temperatures are required to incorporate bismuth or nitrogen into III-V semiconductors. However, the effects of low growth temperature on dark current and responsivity are not well understood. In this work, a set of InGaAs p-i-n wafers were grown at a constant temperature of 250, 300, 400 and 500 °C for all p, i and n layers. A second set of wafers was grown where the p and n layers were grown at 500 °C while the i-layers were grown at 250, 300 and 400 °C. Photodiodes were fabricated from all seven wafers. When constant growth temperature was employed (for all p, i and n layers), we observed that photodiodes grown at 500 °C show dark current density at −1 V that is six orders of magnitude lower while the responsivity at an illumination wavelength of 1520 nm is 4.5 times higher than those from photodiodes grown at 250 °C. Results from the second set of wafers suggest that performance degradation can be recovered by growing the p and n layers at high temperature. For instance, comparing photodiodes with i-layers grown at 250 °C, photodiodes showed dark current density at −1 V that is five orders of magnitude lower when the p and n layers were grown at 500 °C. Postgrowth annealing, at 595 °C for 15 min, on the two wafers grown at 250 and 300 °C showed recovery of diode responsivity but no significant improvement in the dark current. Our work suggests that growth of the cap layer at high temperature is necessary to maintain the responsivity and minimise the dark current degradation, offering a pathway to developing novel photodiode materials that necessitate low growth temperatures. The data reported in this paper is available from the ORDA digital repository (DOI: 10.15131/shef.data.12562346.v1).

Timothy D. Eales, Igor P. Marko, Alf R. Adams, Alexander Andrejew, Kristijonas Vizbaras, Stephen J. Sweeney (2022)The Nature of Auger Recombination in Type-I Quantum Well Lasers Operating in the Mid-Infrared, In: IEEE journal of selected topics in quantum electronics28(1: Semiconductor Lasers)pp. 1-11 IEEE

Auger recombination is known to be a significant non-radiative process limiting near- and mid-infrared quantum well lasers. The one-dimensional confinement of quantum wells and small band offsets (relative to the bandgap) permits two fundamentally different categories of Auger mechanisms to operate. These mechanisms may be identified as either activated or thresholdless in nature. In this work, we investigate the nature of the dominant Auger mechanism in mid-infrared emitting quantum wells by characterizing a range of type-I InGaAsSb quantum well lasers operating within the 2 - 3 μm wavelength range. The temperature dependence of both the threshold current density and integrated spontaneous emission reveal that the threshold current is dominated by radiative recombination up to a break-point temperature (occurring below 200 K). Beyond the break point temperature, the exponential dependence of the threshold current increases rapidly. The deterioration in the stability of lasing threshold indicates that a thermally activated Auger process is dominant in all devices and is sensitive to the population of heavy-holes in the quantum wells.

Timothy D. Eales, Igor P. Marko, Stefan Schulz, Edmond O’Halloran, Seyed Ghetmiri, Wei Du, Yiyin Zhou, Shui-Qing Yu, Joe Margetis, John Tolle, Eoin P. O’Reilly, Stephen J. Sweeney (2019)Ge1-xSnx alloys: Consequences of band mixing effects for the evolution of the band gap ?-character with Sn concentration, In: Scientific Reports Springer Nature

In this work we study the nature of the band gap in GeSn alloys for use in silicon-based lasers. Special attention is paid to Sn-induced band mixing effects. We demonstrate from both experiment and ab-initio theory that the (direct) Γ- character of the GeSn band gap changes continuously with alloy composition and has significant Γ-character even at low (6%) Sn concentrations. The evolution of the Γ-character is due to Sn-induced conduction band mixing effects, in contrast to the sharp indirect-to-direct band gap transition obtained in conventional alloys such as Al1-xGaxAs. Understanding the band mixing effects is critical not only from a fundamental and basic properties viewpoint but also for designing photonic devices with enhanced capabilities utilizing GeSn and related material systems.

KJ Cheetham, A Krier, IP Marko, A Aldukhayel, SJ Sweeney (2011)Direct evidence for suppression of Auger recombination in GaInAsSbP/InAs mid-infrared light-emitting diodes, In: APPL PHYS LETT99(14)141110 AMER INST PHYSICS
T Higashi, SJ Sweeney, AF Phillips, AR Adams, EP O'Reilly, T Uchida, T Fujii (1999)Observation of reduced nonradiative current in 1.3-mu m AlGaInAs-InP strained MQW lasers, In: IEEE PHOTONICS TECHNOLOGY LETTERS11(4)pp. 409-411 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
N Hossain, TJC Hosea, SJ Sweeney, S Liebich, M Zimprich, K Volz, B Kunert, W Stolz (2011)Band structure properties of novel BxGa1-xP alloys for silicon integration, In: JOURNAL OF APPLIED PHYSICS110(6)ARTN 0pp. ?-? AMER INST PHYSICS
S Liebich, M Zimprich, A Beyer, C Lange, DJ Franzbach, S Chatterjee, N Hossain, SJ Sweeney, K Volz, B Kunert, W Stolz (2011)Laser operation of Ga(NAsP) lattice-matched to (001) silicon substrate, In: APPLIED PHYSICS LETTERS99(7)ARTN 0pp. ?-? AMER INST PHYSICS
SL Tan, WM Soong, JE Green, MJ Steer, S Zhang, LJJ Tan, JS Ng, IP Marko, SJ Sweeney, AR Adams, J Allam, JPR David (2013)Experimental evaluation of impact ionization in dilute nitride GaInNAs diodes, In: APPLIED PHYSICS LETTERS103(10)ARTN 1pp. ?-? AMER INST PHYSICS
T Higashi, SJ Sweeney, AF Phillips, AR Adams, EP O'Reilly, T Uchida, T Fujii (1999)Experimental analysis of temperature dependence in 1.3-mu m AlGaInAs-InP strained MQW lasers, In: IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS5(3)pp. 413-419 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
ZL Bushell, Marian Florescu, Stephen Sweeney (2017)High-Q photonic crystal cavities in all-semiconductor photonic crystal heterostructures, In: Physical Review B95(23)235303 American Physical Society

Photonic crystal cavities enable the realization of high Q-factor and low mode-volume resonators, with typical architectures consisting of a thin suspended periodically patterned layer to maximize confinement of light by strong index guiding. We investigate a heterostructure-based approach comprising a high refractive index core and lower refractive index cladding layers. While confinement typically decreases with decreasing index contrast between the core and cladding layers, we show that, counterintuitively, due to the confinement provided by the photonic band structure in the cladding layers, it becomes possible to achieve Q factors > 10 4 with only a small refractive index contrast. This opens up opportunities for implementing high-Q factor cavities in conventional semiconductor heterostructures, with direct applications to the design of electrically pumped nanocavity lasers using conventional fabrication approaches.

AR Mohmad, F Bastiman, CJ Hunter, JS Ng, SJ Sweeney, JPR David (2011)The effect of Bi composition to the optical quality of GaAs1-xBix, In: APPLIED PHYSICS LETTERS99(4)ARTN 0pp. ?-? AMER INST PHYSICS

We report on the pressure dependence of the threshold current in 1.3 mum InGaAsP and 1.5 mum InGaAs quantum-well lasers measured at low temperatures similar to100 K. It was found that the threshold current of both devices slowly increases with increasing pressure (i.e., increasing band gap) at similar to100 K consistent with the calculated variation of the radiative current. In contrast, at room temperature we observed a reduction of the threshold current with increasing pressure. Our low-temperature, high-pressure data confirm the results of previous atmospheric pressure measurements on the same devices which indicated a transition in the dominant recombination mechanism from radiative to Auger as the device temperature is increased from similar to100 to 300 K.

AR Mohmad, F Bastiman, JS Ng, SJ Sweeney, JPR David (2011)Photoluminescence investigation of high quality GaAs1-xBix on GaAs, In: APPLIED PHYSICS LETTERS98(12)ARTN 1pp. ?-? AMER INST PHYSICS
Z Batool, S Chatterjee, A Chernikov, A Duzik, R Fritz, C Gogineni, K Hild, TJC Hosea, S Imhof, SR Johnson, Z Jiang, S Jin, M Koch, SW Koch, K Kolata, RB Lewis, X Lu, M Masnadi-Shirazi, JM Millunchick, PM Mooney, NA Riordan, O Rubel, SJ Sweeney, JC Thomas, A Thränhardt, T Tiedje, K Volz (2013)Bismuth-containing III-V semiconductors: Epitaxial growth and physical propertiespp. 139-158
A Aldukhayel, SR Jin, IP Marko, SJ Sweeney, SY Zhang, DG Revin, JW Cockburn (2013)Investigations of carrier scattering into L-valley in λ=3.5μm InGaAs/AlAs(Sb) quantum cascade lasers using high hydrostatic pressure, In: Physica Status Solidi (B) Basic Research250(4)pp. 693-697

In order to identify the performance limitations of InGaAs/AlAs(Sb) quantum cascade lasers, experimental investigations of the temperature and pressure dependencies of the threshold current (I) were undertaken. Using the theoretical optical phonon current (I) and carrier leakage (I) to fit the measured threshold current at various pressures, we show that the electron scattering from the top lasing level to the upper L-minima gives rise to the increase in I with pressure and temperature. It was found that this carrier leakage path accounts for approximately 3% of I at RT and is negligible at 100K. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

BG Crutchley, IP Marko, SJ Sweeney, J Pal, MA Migliorato (2013)Optical properties of InGaN-based LEDs investigated using high hydrostatic pressure dependent techniques, In: Physica Status Solidi (B) Basic Research250(4)pp. 698-702

High pressure electroluminescence (EL) measurements were carried out on blue and green emitting InGaN-based light emitting diodes (LEDs). The weak pressure coefficient of the peak emission energy of the LEDs is found to increase with increasing injection current. Such behaviour is consistent with an enhancement of the piezoelectric fields under high pressure which become increasingly screened at high currents. A subsequent increase in the quantum confined Stark effect (QCSE) is expected to cause a reduction of the light output power as pressure is applied at a fixed low current density (∼10Acm). A similar proportional reduction of light output power as pressure is applied at a fixed high current density (260Acm) suggests that there is a non-radiative loss process in these devices which is relatively insensitive to pressure. Such behaviour is shown to be consistent with a defect-related recombination process which increases with increasing injection. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

M Usman, CA Broderick, Z Batool, K Hild, TJC Hosea, SJ Sweeney, EP O'Reilly (2013)Impact of alloy disorder on the band structure of compressively strained GaBixAs1-x, In: PHYSICAL REVIEW B87(11)ARTN 1pp. ?-? AMER PHYSICAL SOC
J Mukherjee, S Jarvis, SJ Sweeney, M Perren (2013)Efficiency limits of laser power converters for optical power transfer applications, In: Journal of Physics D: Applied Physics46(26)

We have developed III-V-based high-efficiency laser power converters (LPCs), optimized specifically for converting monochromatic laser radiation at the eye-safe wavelength of 1.55 m into electrical power. The applications of these photovoltaic cells include high-efficiency space-based and terrestrial laser power transfer and subsequent conversion to electrical power. In addition, these cells also find use in fibre-optic power delivery, remote powering of subcutaneous equipment and several other optical power delivery applications. The LPC design is based on lattice-matched InGaAsP/InP and incorporates elements for photon-recycling and contact design for efficient carrier extraction. Here we compare results from electro-optical design simulations with experimental results from prototype devices studied both in the lab and in field tests. We analyse wavelength and temperature dependence of the LPC characteristics. An experimental conversion efficiency of 44.6% [±1%] is obtained from the prototype devices under monochromatic illumination at 1.55 m (illumination power density of 1 kW m) at room temperature. Further design optimization of our LPC is expected to scale the efficiency beyond 50% at 1 kW m. © 2013 IOP Publishing Ltd.

GT Reed, DJ Thomson, FY Gardes, Y Hu, N Owens, X Yang, P Petropoulos, K Debnath, L O'Faolain, TF Krauss, L Lever, Z Ikonic, RW Kelsall, M Myronov, DR Leadley, IP Marko, SJ Sweeney, DC Cox, A Brimont, P Sanchis, G-H Duan, A Le Liepvre, C Jany, M Lamponi, D Make, F Lelarge, JM Fedeli, S Messaoudene, S Keyvaninia, G Roelkens, D Van Thourhout, S Liu (2012)High performance silicon optical modulators, In: Proceedings of SPIE - The International Society for Optical Engineering8564

In this work we present results from high performance silicon optical modulators produced within the two largest silicon photonics projects in Europe; UK Silicon Photonics (UKSP) and HELIOS. Two conventional MZI based optical modulators featuring novel self-aligned fabrication processes are presented. The first is based in 400nm overlayer SOI and demonstrates 40Gbit/s modulation with the same extinction ratio for both TE and TM polarisations, which relaxes coupling requirements to the device. The second design is based in 220nm SOI and demonstrates 40Gbits/s modulation with a 10dB extinction ratio as well modulation at 50Gbit/s for the first time. A ring resonator based optical modulator, featuring FIB error correction is presented. 40Gbit/s, 32fJ/bit operation is also shown from this device which has a 6um radius. Further to this slow light enhancement of the modulation effect is demonstrated through the use of both convention photonic crystal structures and corrugated waveguides. Fabricated conventional photonic crystal modulators have shown an enhancement factor of 8 over the fast light case. The corrugated waveguide device shows modulation efficiency down to 0.45V.cm compared to 2.2V.cm in the fast light case. 40Gbit/s modulation is demonstrated with a 3dB modulation depth from this device. Novel photonic crystal based cavity modulators are also demonstrated which offer the potential for low fibre to fibre loss. In this case preliminary modulation results at 1Gbit/s are demonstrated. Ge/SiGe Stark effect devices operating at 1300nm are presented. Finally an integrated transmitter featuring a III-V source and MZI modulator operating at 10Gbit/s is presented. © 2012 SPIE.

P Ludewig, N Knaub, N Hossain, S Reinhard, L Nattermann, IP Marko, SR Jin, K Hild, S Chatterjee, W Stolz, SJ Sweeney, K Volz (2013)Electrical injection Ga(AsBi)/(AlGa)As single quantum well laser, In: APPLIED PHYSICS LETTERS102(24)ARTN 2pp. ?-? AMER INST PHYSICS
IP Marko, SR Jin, K Hild, Z Batool, ZL Bushell, P Ludewig, W Stolz, K Volz, R Butkute, V Pacebutas, A Geizutis, A Krotkus, SJ Sweeney (2015)Properties of hybrid MOVPE/MBE grown GaAsBi/GaAs based near-infrared emitting quantum well lasers, In: SEMICONDUCTOR SCIENCE AND TECHNOLOGY30(9)ARTN 0pp. ?-? IOP PUBLISHING LTD
Zoe L. Bushell, Christopher A. Broderick, Lukas Nattermann, Rita Joseph, Joseph L. Keddie, Judy M. Rorison, Kerstin Volz, Stephen J. Sweeney (2019)Giant bowing of the band gap and spin-orbit splitting energy in GaP1−χBiχ dilute bismide alloys, In: Scientific Reports9(1)6835 Nature Research

Using spectroscopic ellipsometry measurements on GaP1−χBiχ/GaP epitaxial layers up to χ = 3.7% we observe a giant bowing of the direct band gap (EΓg) and valence band spin-orbit splitting energy (ΔSO). EΓg (ΔSO) is measured to decrease (increase) by approximately 200 meV (240 meV) with the incorporation of 1% Bi, corresponding to a greater than fourfold increase in ΔSO in going from GaP to GaP0.99Bi0.01. The evolution of EΓg and ΔSO with χ is characterised by strong, composition-dependent bowing. We demonstrate that a simple valence band-anticrossing model, parametrised directly from atomistic supercell calculations, quantitatively describes the measured evolution of EΓg and ΔSO with χ. In contrast to the well-studied GaAs1−χBiχ alloy, in GaP1−χBiχ substitutional Bi creates localised impurity states lying energetically within the GaP host matrix band gap. This leads to the emergence of an optically active band of Bi-hybridised states, accounting for the overall large bowing of EΓg and ΔSO and in particular for the giant bowing observed for χ ≲ 1%. Our analysis provides insight into the action of Bi as an isovalent impurity, and constitutes the first detailed experimental and theoretical analysis of the GaP1−χBiχ alloy band structure.

SJ Sweeney, AF Phillips, AR Adams, EP O'Reilly, PJA Thijs (1998)The effect of temperature dependent processes on the performance of 1.5-mu m compressively strained InGaAs(P) MQW semiconductor diode lasers, In: IEEE PHOTONICS TECHNOLOGY LETTERS10(8)pp. 1076-1078 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
S. R. Jin, C. N. Ahmad, S. J. Sweeney, A. R. Adams, B. N. Murdin, H. Page, X. Marcadet, C. Sirtori, S. Tomić (2006)Spectroscopy of GaAs/AlGaAs quantum-cascade lasers using hydrostatic pressure, In: Applied Physics Letters221105(2006)
RA Simmons, SR Jin, SJ Sweeney, SK Clowes (2015)Enhancement of Rashba interaction in GaAs/AlGaAs quantum wells due to the incorporation of bismuth, In: APPLIED PHYSICS LETTERS107(14)ARTN 1 AMER INST PHYSICS

This paper reports on the predicted increase in the Rashba interaction due to the incorporation of Bi in GaAs/AlGaAs heterostructures. Band structure parameters obtained from the band anti-crossing theory have been used in combination with self-consistent Schrödinger-Poisson calculations and k.p models to determine the electron spin-splitting caused by structural inversion asymmetry and increased spin-orbit interaction. A near linear seven fold increase in the strength of the Rashba interaction is predicted for a 10% concentration of Bi in a GaAsBi/AlGaAs quantum well heterostructure.

SJ Sweeney, T Higashi, AR Adams, T Uchida, T Fujii (1998)Improved temperature dependence of 1.3 mu m AlGalnAs-based MQW semiconductor diode lasers revealed by hydrostatic pressure, In: ELECTRONICS LETTERS34(22)pp. 2130-2132 IEE-INST ELEC ENG
K O'Brien, SJ Sweeney, AR Adams, BN Murdin, A Salhi, Y Rouillard, A Joullie (2006)Recombination processes in midinfrared InGaAsSb diode lasers emitting at 2.37 mu m, In: APPLIED PHYSICS LETTERS89(5)ARTN 0pp. ?-? AMER INST PHYSICS
SD Jarvis, J Mukherjee, M Perren, SJ Sweeney (2014)Development and characterisation of laser power converters for optical power transfer applications, In: IET OPTOELECTRONICS8(2)pp. 64-70 INST ENGINEERING TECHNOLOGY-IET
J Chamings, AR Adams, SJ Sweeney, B Kunert, K Volz, W Stolz (2008)Temperature dependence and physical properties of Ga(NAsP)/GaP semiconductor lasers, In: APPLIED PHYSICS LETTERS93(10)ARTN 1pp. ?-? AMER INST PHYSICS
JV Pearce, O Ongrai, G Machin, SJ Sweeney (2010)Self-validating thermocouples based on high temperature fixed points, In: METROLOGIA47(1)pp. L1-L3 IOP PUBLISHING LTD
S Tan, CJ Hunter, S Zhang, LJJ Tan, YL Goh, JS Ng, JPR David, Igor Marko, Stephen Sweeney, Alfred Adams, Jeremy Allam (2012)Improved optoelectronic properties of rapid thermally annealed dilute nitride GaInNAs photodetectors, In: Journal of Electronic Materials41(12)pp. 3393-3401 IEEE

We investigate the optical and electrical characteristics of GaInNAs/GaAs long-wavelength photodiodes grown under varying conditions by molecular beam epitaxy and subjected to postgrowth rapid thermal annealing (RTA) at a series of temperatures. It is found that the device performance of the nonoptimally grown GaInNAs p-i-n structures, with nominal compositions of 10% In and 3.8% N, can be improved significantly by the RTA treatment to match that of optimally grown structures. The optimally annealed devices exhibit overall improvement in optical and electrical characteristics, including increased photoluminescence brightness, reduced density of deep-level traps, reduced series resistance resulting from the GaAs/GaInNAs heterointerface, lower dark current, and significantly lower background doping density, all of which can be attributed to the reduced structural disorder in the GaInNAs alloy.© 2012 TMS.

S Sweeney (2011)Selected papers from the Semiconductor and Integrated Optoelectronics (SIOE'10) Conference, In: IET OPTOELECTRONICS5(3)pp. 99-99 INST ENGINEERING TECHNOLOGY-IET
I Marko, S Sweeney, K hild (2016)Temperature stable mid-infrared GaInAsSb/GaSb Vertical Cavity Surface Emitting Lasers (VCSELs), In: Scientific Reports619595 Nature Publishing Group

GaInAsSb/GaSb based quantum well vertical cavity surface emitting lasers (VCSELs) operating in mid-infrared spectral range between 2 and 3 micrometres are of great importance for low cost gas monitoring applications. This paper discusses the efficiency and temperature sensitivity of the VCSELs emitting at 2.6 μm and the processes that must be controlled to provide temperature stable operation. We show that non-radiative Auger recombination dominates the threshold current and limits the device performance at room temperature. Critically, we demonstrate that the combined influence of non-radiative recombination and gain peak – cavity mode de-tuning determines the overall temperature sensitivity of the VCSELs. The results show that improved temperature stable operation around room temperature can only be achieved with a larger gain peak – cavity mode de-tuning, offsetting the significant effect of increasing non-radiative recombination with increasing temperature, a physical effect which must be accounted for in mid-infrared VCSEL design.

Igor Marko, Stephen Sweeney (2017)Progress towards III-V-Bismide Alloys for Near- and Mid-Infrared Laser Diodes, In: IEEE Journal of Selected Topics in Quantum Electronics23(6)1501512 Institute of Electrical and Electronics Engineers (IEEE)

Bismuth-containing III-V alloys open-up a range of possibilities for practical applications in semiconductor lasers, photovoltaics, spintronics, photodiodes and thermoelectrics. Of particular promise for the development of semiconductor lasers is the possibility to grow GaAsBi laser structures such that the spin-orbit-splitting energy (ΔSO) is greater than the bandgap (Eg) in the active region for devices operating around the telecom wavelength of 1.55 μm, thereby suppressing the dominant efficiency-limiting loss processes in such lasers, namely Auger recombination and inter-valence band absorption (IVBA). The ΔSO > Eg band structure is present in GaAsBi alloys containing > 10% Bi, at which composition the alloy band gap is close to 1.55 μm on a GaAs substrate making them an attractive candidate material system for the development of highly efficient, uncooled GaAs-based lasers for telecommunications. Here we discuss progress towards this goal and present a comprehensive set of data on the properties of GaAsBi lasers including optical gain and absorption characteristics and the dominant carrier recombination processes in such systems. Finally, we briefly review the potential of GaAsBiN and InGaAsBi material systems for near- and mid-infrared photonic devices on GaAs and InP platforms, respectively.

R Fehse, SJ Sweeney, AR Adams, EP O'Reilly, AY Egorov, H Riechert, S Illek (2001)Insights into carrier recombination processes in 1.3 mu m GaInNAs-based semiconductor lasers attained using high pressure, In: ELECTRONICS LETTERS37(2)pp. 92-93 IEE-INST ELEC ENG
AF Phillips, SJ Sweeney, AR Adams, PJA Thijs (1999)The temperature dependence of 1.3-and 1.5-mu m compressively strained InGaAs(P) MQW semiconductor lasers, In: IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS5(3)pp. 401-412 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
R Fehse, S Jin, SJ Sweeney, AR Adams, EP O'Reilly, H Riechert, S Illek, AY Egorov (2001)Evidence for large monomolecular recombination contribution to threshold current in 1.3 mu m GaInNAs semiconductor lasers, In: ELECTRONICS LETTERS37(25)pp. 1518-1520 IEE-INST ELEC ENG
AR Mohmad, F Bastiman, CJ Hunter, RD Richards, SJ Sweeney, JS Ng, JPR David, BY Majlis (2014)Localization effects and band gap of GaAsBi alloys, In: PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS251(6)pp. 1276-1281 WILEY-V C H VERLAG GMBH
TE Sale, SJ Sweeney, G Knowles, AR Adams (2001)Gain-cavity alignment in efficient visible (660 nm) VCSELs studied using high pressure techniques, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH223(2)pp. 587-591 WILEY-V C H VERLAG GMBH
M. K. Sharpe, I. P. Marko, D. A. Duffy, J. England, E. Schneider, M. Kesaria, V. Fedorov, E. Clarke, C. H. Tan, S. J. Sweeney (2019)A comparative study of epitaxial InGaAsBi/InP structures using Rutherford backscattering spectrometry, X-ray diffraction and photoluminescence techniques, In: JOURNAL OF APPLIED PHYSICS126(12)125706 AMER INST PHYSICS

In this work, we used a combination of photoluminescence (PL), high resolution X-ray diffraction (XRD), and Rutherford backscattering spectrometry (RBS) techniques to investigate material quality and structural properties of MBE-grown InGaAsBi samples (with and without an InGaAs cap layer) with targeted bismuth composition in the 3%–4% range. XRD data showed that the InGaAsBi layers are more homogeneous in the uncapped samples. For the capped samples, the growth of the InGaAs capped layer at higher temperature affects the quality of the InGaAsBi layer and bismuth distribution in the growth direction. Low-temperature PL exhibited multiple emission peaks; the peak energies, widths, and relative intensities were used for comparative analysis of the data in line with the XRD and RBS results. RBS data at a random orientation together with channeled measurements allowed both an estimation of the bismuth composition and analysis of the structural properties. The RBS channeling showed evidence of higher strain due to possible antisite defects in the capped samples grown at a higher temperature. It is also suggested that the growth of the capped layer at high temperature causes deterioration of the bismuth-layer quality. The RBS analysis demonstrated evidence of a reduction of homogeneity of uncapped InGaAsBi layers with increasing bismuth concentration. The uncapped higher bismuth concentration sample showed less defined channeling dips suggesting poorer crystal quality and clustering of bismuth on the sample surface.

SR Jin, R Fehse, SJ Sweeney, G Knowles, AR Adams, EP O'Reilly, H Reichert, S Illek, AY Egorov, PJA Thijs, T Uchida, T Fujii (2002)Modal refractive index of 1.3 mu m InGaAsP, AlGaInAs and GaInNAs semiconductor lasers under high hydrostatic pressure, In: ELECTRONICS LETTERS38(7)pp. 325-327 IEE-INST ELEC ENG
G Knowles, SJ Sweeney, TE Sale, AR Adams (2001)Self-heating effects in red (665 nm) VCSELs, In: IEE PROCEEDINGS-OPTOELECTRONICS148(5-6)PII 10.104pp. 256-260 IEE-INST ELEC ENG
R Fehse, S Tomic, AR Adams, SJ Sweeney, EP O'Reilly, A Andreev, H Riechert (2002)A quantitative study of radiative, Auger, and defect related recombination processes in 1.3-mu m GaInNAs-based quantum-well lasers, In: IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS8(4)pp. 801-810 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
JS Ng, WM Soong, MJ Steer, M Hopkinson, JPR David, J Chamings, SJ Sweeney, AR Adams (2007)Long wavelength bulk GaInNAs p-i-n photodiodes lattice matched to GaAs, In: JOURNAL OF APPLIED PHYSICS101(6)ARTN 0pp. ?-? AMER INST PHYSICS
SR Jin, Stephen Sweeney, S Tomic, Alfred Adams, H Riechert (2003)High-pressure studies of recombination mechanisms in 1.3-mu m GaInNAs quantum-well lasers, In: IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS9(5)pp. 1196-1201 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

The pressure dependence of the components of the recombination current at threshold in 1.3-mum GaInNAs single quantum-well lasers is presented using for the first time high-pressure spontaneous emission measurements up to 13 kbar. It is shown that, above 6 kbar, the rapid increase of the threshold current With increasing pressure is associated with the unusual increase of the Auger-related nonradiative recombination current, while the defect-related monomolecular nonradiative recombination current is almost constant. Theoretical calculations show that the increase of the Auger current can be attributed to a large increase in the threshold carrier density with pressure, Which is mainly due to the increase in the electron effective mass arising from the enhanced level-anticrossing between the GaInNAs conduction band and the nitrogen level.

K Hild, TE Sale, SJ Sweeney, M Hirotani, Y Mizuno, T Kato (2004)Modulation speed resonant-cavity and leakage current in 650 nm light emitting diodes, In: IEE PROCEEDINGS-OPTOELECTRONICS151(2)pp. 94-97 IEE-INST ELEC ENG

The authors have investigated red-emitting (650 nm) resonant-cavity light emitting diodes for use with polymer optical fibres. The small signal modulation response is characterised by a single order roll-off. The -3 dB bandwidth is found to be determined solely by the differential carrier lifetime, T, in the active region and hence dependent on current density, J, alone with no intrinsic size effects. The tau(J) relation allows the calculation of the active region carrier density and hence the recombination parameters (mono- and bimolecular) in the regime where the leakage is small. It is shown that the leakage is insignificant for currents below 200 A/cm(2) at 20degreesC. Above 40degreesC the leakage rises rapidly with temperature, and is evident from a dramatic fall in tau and an accelerated rise in the current required to maintain constant light output.

NF Masse, AR Adams, SJ Sweeney (2007)Experimental determination of the band gap dependence of Auger recombination in InGaAs/InP multiple quantum well lasers at room temperature, In: APPLIED PHYSICS LETTERS90(16)ARTN 1pp. ?-? AMER INST PHYSICS

The band gap dependencies of the threshold current and its radiative component are measured using high pressure techniques. Detailed theoretical calculations show that the band gap dependence of the internal losses plays a significant role in the band gap dependence of the radiative current. Temperature dependence measurements show that the radiative current accounts for 20% of the total threshold current at room temperature. This allows us to determine the pressure dependence of the non-radiative Auger recombination current, and hence to experimentally obtain the variation of the Auger coefficient C with band gap. (c) 2007 American Institute of Physics.

SR Jin, SJ Sweeney, S Tomic, AR Adams, H Riechert (2003)Unusual increase of the Auger recombination current in 1.3 mu m GaInNAs quantum-well lasers under high pressure, In: APPLIED PHYSICS LETTERS82(14)pp. 2335-2337 AMER INST PHYSICS
SB Constant, S Tomic, D Lock, TE Sale, SJ Sweeney, TJC Hosea (2003)Spectroscopic characterization of 1450 nm semiconductor pump laser structures for Raman amplifiers, In: JOURNAL OF APPLIED PHYSICS93(12)pp. 9446-9455 AMER INST PHYSICS
AD Prins, MK Lewis, ZL Bushell, SJ Sweeney, S Liu, Y-H Zhang (2015)Evidence for a defect level above the conduction band edge of InAs/InAsSb type-II superlattices for applications in efficient infrared photodetectors, In: APPLIED PHYSICS LETTERS106(17)ARTN 1 AMER INST PHYSICS

We report pressure-dependent photoluminescence (PL) experiments under hydrostatic pressures up to 2.16 GPa on a mid-wave infrared InAs/InAs0.86Sb0.14 type-II superlattice (T2SL) structure at different pump laser excitation powers and sample temperatures. The pressure coefficient of the T2SL transition was found to be 93 ± 2 meV·GPa-1. The integrated PL intensity increases with pressure up to 1.9 GPa then quenches rapidly indicating a pressure induced level crossing with the conduction band states at ∼2 GPa. Analysis of the PL intensity as a function of excitation power at 0, 0.42, 1.87, and 2.16 GPa shows a clear change in the dominant photo-generated carrier recombination mechanism from radiative to defect related. From these data, evidence for a defect level situated at 0.18 ± 0.01 eV above the conduction band edge of InAs at ambient pressure is presented. This assumes a pressure-dependent energy shift of -11 meV·GPa-1 for the valence band edge and that the defect level is insensitive to pressure, both of which are supported by an Arrhenius activation energy analysis.

C Bueckers, G Blume, A Thraenhardt, C Schlichenmaier, PJ Klar, G Weiser, SW Koch, J Hader, JV Moloney, Thomas Hosea, Stephen Sweeney, J-B Wang, SR Johnson, Y-H Zhang (2007)Microscopic electroabsorption line shape analysis for Ga(AsSb)/GaAs heterostructures, In: JOURNAL OF APPLIED PHYSICS101(3)ARTN 0pp. ?-? AMER INST PHYSICS

A series of Ga(AsSb)/GaAs/(AlGa) As samples with varying GaAs spacer width are studied by electric-field modulated absorption (EA) and reflectance spectroscopy and modeled using a microscopic theory. The analysis of the Franz-Keldysh oscillations of GaAs capping layer and of the quantum-confined Stark shift of the lowest quantum well (QW) transitions shows the strong inhomogeneity of the built-in electric field indicating that the field modulation due to an external bias voltage differs significantly for the various regions of the structures. The calculations demonstrate that the line shape of the EA spectra of these samples is extremely sensitive to the value of the small conduction band offset between GaAs and Ga(AsSb) as well as to the magnitude of the internal electric field changes caused by the external voltage modulation in the QW region. The EA spectra of the entire series of samples are modeled by the microscopic theory. The good agreement between experiment and theory allows us to extract the strength of the modulation of the built-in electric field in the QW region and to show that the band alignment between GaAs and Ga(AsSb) is of type II with a conduction band offset of approximately 40 meV.

CA Broderick, S Jin, Igor Marko, Konstanze Hild, P Ludewig, Zoe Bushell, W Stolz, JM Rorison, EP O’Reilly, K Volz, Stephen Sweeney (2017)GaAs1−xBix/GaNyAs1−y type-II quantum wells: novel strain-balanced heterostructures for GaAs-based near- and mid-infrared photonics, In: Scientific Reports746371 Nature Publishing Group

The potential to extend the emission wavelength of photonic devices further into the near- and midinfrared via pseudomorphic growth on conventional GaAs substrates is appealing for a number of communications and sensing applications. We present a new class of GaAs-based quantum well (QW) heterostructure that exploits the unusual impact of Bi and N on the GaAs band structure to produce type-II QWs having long emission wavelengths with little or no net strain relative to GaAs, while also providing control over important laser loss processes. We theoretically and experimentally demonstrate the potential of GaAs1−xBix/GaNyAs1−y type-II QWs on GaAs and show that this approach offers optical emission and absorption at wavelengths up to ~3 μm utilising strain-balanced structures, a first for GaAs-based QWs. Experimental measurements on a prototype GaAs0.967Bi0.033/GaN0.062As0.938 structure, grown via metal-organic vapour phase epitaxy, indicate good structural quality and exhibit both photoluminescence and absorption at room temperature. The measured photoluminescence peak wavelength of 1.72 μm is in good agreement with theoretical calculations and is one of the longest emission wavelengths achieved on GaAs to date using a pseudomorphically grown heterostructure. These results demonstrate the significant potential of this new class of III-V heterostructure for longwavelength applications.

J Chamings, S Ahmed, SJ Sweeney, VA Odnoblyudov, CW Tu (2008)Physical properties and efficiency of GaNP light emitting diodes, In: APPLIED PHYSICS LETTERS92(2)ARTN 0pp. ?-? AMER INST PHYSICS
S. R. Jin, S. J. Sweeney, C. N. Ahmad, A. R. Adams, B. N. Murdin (2004)Radiative and Auger recombination in 1.3 µm InGaAsP and 1.5 µm InGaAs quantum-well lasers measured under high pressure at low and room temperatures, In: Applied Physics Letters357(2004)

We report on the pressure dependence of the threshold current in 1.3 µm InGaAsP and 1.5 µm InGaAs quantum-well lasers measured at low temperatures ~100 K. It was found that the threshold current of both devices slowly increases with increasing pressure (i.e., increasing band gap) at ~100 K consistent with the calculated variation of the radiative current. In contrast, at room temperature we observed a reduction of the threshold current with increasing pressure. Our low-temperature, high-pressure data confirm the results of previous atmospheric pressure measurements on the same devices which indicated a transition in the dominant recombination mechanism from radiative to Auger as the device temperature is increased from ~100 to 300 K

S Tomic, EP O'Reilly, R Fehse, Stephen Sweeney, Alfred Adams, Aleksey Andreev, SA Choulis, Thomas Hosea, H Riechert (2003)Theoretical and experimental analysis of 1.3-mu m InGaAsN/GaAs lasers, In: IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS9(5)pp. 1228-1238 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

We present a comprehensive theoretical and experimental analysis of 1.3-mum InGaAsN/GaAs lasers. After introducing the 10-band k . p Hamiltonian which predicts transition energies observed experimentally, we employ it to investigate laser properties of ideal and real InGaAsN/GaAs laser devices. Our calculations show that the addition of N reduces the peak gain and differential gain at fixed carrier density, although the gain saturation value and the peak gain as a function of radiative current density are largely unchanged due to the incorporation of N. The gain characteristics are optimized by including the minimum amount of nitrogen necessary to prevent strain relaxation at the given well thickness. The measured spontaneous emission and gain characteristics of real devices are well described by the theoretical model. Our analysis shows that the threshold current is dominated by nonradiative, defect-related recombination. Elimination of these losses would enable laser characteristics comparable with the best InGaAsP/InP-based lasers with the added advantages provided by the GaAs system that are important for vertical integration.

S Buaprathoom, S Pedley, AD Prins, SJ Sweeney, F Berghmans, AG Mignani, P DeMoor (2012)High concentration measurement of mixed particle suspensions using simple multi-angle light scattering system, In: OPTICAL SENSING AND DETECTION II8439ARTN 8pp. ?-? SPIE-INT SOC OPTICAL ENGINEERING
O Ongrai, JV Pearce, G Machin, SJ Sweeney (2013)Self-calibration of a W/Re thermocouple using a miniature Ru-C (1954 °c) eutectic cell, In: AIP Conference Proceedings1552 8pp. 504-509

Previous successful investigations of miniature cobalt-carbon (Co-C, 1324 °C) and palladium-carbon (Pd-C, 1492 °C) high temperature fixed-point cells for thermocouple self-calibration have been reported [1-2]. In the present work, we describe a series of measurements of a miniature ruthenium-carbon (Ru-C) eutectic cell (melting point 1954 °C) to evaluate the repeatability and stability of a W/Re thermocouple (type C) by means of in-situ calibration. A miniature Ru-C eutectic fixed-point cell with outside diameter 14 mm and length 30 mm was fabricated to be used as a self-calibrating device. The performance of the miniature Ru-C cell and the type C thermocouple is presented, including characterization of the stability, repeatability, thermal environment influence, ITS-90 temperature realization and measurement uncertainty.

Ross Maspero, Stephen Sweeney, Marian Florescu (2016)Unfolding the band structure of GaAsBi, In: Journal of Physics: Condensed Matter29(7)075001 Institute of Physics

Typical supercell approaches used to investigate the electronic properties of GaAs(1−x)Bi(x) produce highly accurate, but folded, band structures. Using a highly optimized algorithm, we unfold the band structure to an approximate $E____left(____mathbf{k}____right)$ relation associated with an effective Brillouin zone. The dispersion relations we generate correlate strongly with experimental results, confirming that a regime of band gap energy greater than the spin–orbit-splitting energy is reached at around 10% bismuth fraction. We also demonstrate the effectiveness of the unfolding algorithm throughout the Brillouin zone (BZ), which is key to enabling transition rate calculations, such as Auger recombination rates. Finally, we show the effect of disorder on the effective masses and identify approximate values for the effective mass of the conduction band and valence bands for bismuth concentrations from 0–12%.

K. O'Brien, S. J. Sweeney, A. R. Adams, B. N Murdin, A. Salhi, Y. Rouillard, A. Joullié (2006)Recombination processes in midinfrared InGaAsSb diode lasers emitting at 2.37 µm, In: Applied Physics Letters051104(2006)

The temperature dependence of the threshold current of InGaAsSb/AlGaAsSb compressively strained lasers is investigated by analyzing the spontaneous emission from working laser devices through a window formed in the substrate metallization and by applying high pressures. It is found that nonradiative recombination accounts for 80% of the threshold current at room temperature and is responsible for the high temperature sensitivity. The authors suggest that Auger recombination involving hot holes is suppressed in these devices because the spin-orbit splitting energy is larger than the band gap, but other Auger processes persist and are responsible for the low T0 values.

Alfred Adams, Igor Marko, J Mukherjee, Vlad Stolojan, Stephen Sweeney, A Gocalinska, E Pelucchi, K Thomas, B Corbett (2015)Semiconductor Quantum Well Lasers With a Temperature-Insensitive Threshold Current, In: IEEE Journal of Selected Topics in Quantum Electronics21(6)150080pp. ?-? IEEE

This paper proposes and demonstrates a new multiquantum well (MQW) laser structure with a temperature-insensitive threshold current and output power. Normally, the mechanisms that cause the threshold current (Ith) of semiconductor lasers to increase with increasing temperature T (thermal broadening of the gain spectrum, thermally activated carrier escape, Auger recombination, and intervalence band absorption) act together to cause Ith to increase as T increases. However, in the design presented here, carriers thermally released from some of the QWs are fed to the other QWs so that these mechanisms compensate rather than augment one another. The idea is in principle applicable to a range of materials systems, structures, and operating wavelengths. We have demonstrated the effect for the first time in 1.5 μm GaInAsP/InP Fabry-Perot cavity edge-emitting lasers. The results showed that it is possible to keep the threshold current constant over a temperature range of about 100 K and that the absolute temperature over which the plateau occurred could be adjusted easily by redesigning the quantum wells and the barriers between them. TEM studies of the structures combined with measurements of the electroluminescent intensities from the wells are presented and explain well the observed effects.

SJ Sweeney, T Higashi, A Andreev, AR Adams, T Uchida, T Fujii (2001)Superior temperature performance of 1.3 mu m AlGaInAs-Based semiconductor lasers investigated at high pressure and low temperature, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH223(2)pp. 573-579 WILEY-V C H VERLAG GMBH
A Jha, SJ Sweeney (2015)Optical, optoelectronic and photonic materials and applications Preface, In: SEMICONDUCTOR SCIENCE AND TECHNOLOGY30(4)ARTN 04030 IOP PUBLISHING LTD
N Hossain, SR Jin, S Liebich, M Zimprich, K Volz, B Kunert, W Stolz, SJ Sweeney (2012)Efficiency-limiting processes in Ga(NAsP)/GaP quantum well lasers, In: APPLIED PHYSICS LETTERS101(1)ARTN 0pp. ?-? AMER INST PHYSICS
SJ Sweeney, G Knowles, TE Sale, AR Adams (2001)Quantifying the effect of indirect carrier leakage on visible Al(GaInP) lasers using high pressures and low temperatures, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH223(2)pp. 567-572 WILEY-V C H VERLAG GMBH
Igor Marko, GW Read, N Hossain, Stephen Sweeney (2015)Physical Properties and Characteristics of III-V Lasers on Silicon, In: IEEE Journal of Selected Topics in Quantum Electronics21(6)1502208 IEEE

The development of laser technology based on silicon continues to be of key importance for the advancement of electronic-photonic integration offering the potential for high data rates and reduced energy consumption. Progress was initially hindered due to the inherent indirect band gap of silicon. However, there has been considerable progress in developing ways of incorporating high gain III-V based direct band gap materials onto silicon, bringing about the advantages of both materials. In this paper, we introduce the need for lasers on silicon and review some of the main approaches for the integration of III-V active regions, including direct epitaxial growth, hybrid integration, defect blocking layers and quantum dots. We then discuss the roles of different carrier recombination processes on the performance of devices formed using both wafer fusion and direct epitaxial approaches.

Z Batool, K Hild, TJC Hosea, X Lu, T Tiedje, SJ Sweeney (2012)The electronic band structure of GaBiAs/GaAs layers: Influence of strain and band anti-crossing, In: JOURNAL OF APPLIED PHYSICS111(11)ARTN 1pp. ?-? AMER INST PHYSICS
GMT Chai, TJC Hosea, NE Fox, K Hild, AB Ikyo, IP Marko, SJ Sweeney, A Bachmann, S Arafin, M-C Amann (2014)Characterization of 2.3 mu m GaInAsSb-based vertical-cavity surface-emitting laser structures using photo-modulated reflectance, In: JOURNAL OF APPLIED PHYSICS115(1)ARTN 0pp. ?-? AMER INST PHYSICS
Stephen Sweeney, LJ Lyons, Alfred Adams, DA Lock (2003)Direct measurement of facet temperature up to melting point and COD in high-power 980-nm semiconductor diode lasers, In: IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS9(5)pp. 1325-1332 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

The authors describe a straightforward experimental technique for measuring the facet temperature of a semiconductor laser under high-power operation by analyzing the laser emission itself. By applying this technique to 1-mm-long 980-nm lasers with 6- and 9-mum-wide tapers, they measure a large increase in facet temperature under both continuous wave (CW) and pulsed operation. Under CW operation, the facet temperature increases from similar to25 degreesC at low currents to over 140 degreesC at 500 mA. From pulsed measurements they observe a sharper rise in facet temperature as a function of current (similar to 400 degreesC at 500 mA) when compared with the CW measurements. This difference is caused by self-heating which limits the output power and hence facet temperature under CW operation. Under pulsed operation the maximum measured facet temperature was in excess of 1000 degreesC for a current of 1000 mA. Above this current, both lasers underwent. catastrophic optical damage (COD). These results show a striking increase in facet temperature under high-power operation consistent with the facet melting at COD. This is made possible by measuring the laser under pulsed operation.

SR Jin, CN Ahmad, SJ Sweeney, AR Adams, BN Murdin, H Page, X Marcadet, C Sirtori, S Tomic (2006)Spectroscopy of GaAs/AlGaAs quantum-cascade lasers using hydrostatic pressure, In: APPLIED PHYSICS LETTERS89(22)ARTN 2pp. ?-? AMER INST PHYSICS
K Hild, IP Marko, SR Johnson, S-Q Yu, Y-H Zhang, SJ Sweeney (2011)Influence of de-tuning and non-radiative recombination on the temperature dependence of 1.3 mu m GaAsSb/GaAs vertical cavity surface emitting lasers, In: APPLIED PHYSICS LETTERS99(7)ARTN 0pp. ?-? AMER INST PHYSICS
SA Sayid, IP Marko, SJ Sweeney, P Barrios, PJ Poole (2010)Efficiency limiting processes in 1.55 mu m InAs/InP-based quantum dots lasers, In: APPLIED PHYSICS LETTERS97(16)ARTN 1pp. ?-? AMER INST PHYSICS
J Pal, MA Migliorato, C-K Li, Y-R Wu, BG Crutchley, IP Marko, SJ Sweeney (2013)Enhancement of efficiency of InGaN-based light emitting diodes through strain and piezoelectric field management, In: Journal of Applied Physics114(7)

We report calculations of the strain dependence of the piezoelectric field within InGaN multi-quantum wells light emitting diodes. Such fields are well known to be a strong limiting factor of the device performance. By taking into account the nonlinear piezoelectric coefficients, which in particular cases predict opposite trends compared to the commonly used linear coefficients, a significant improvement of the spontaneous emission rate can be achieved as a result of a reduction of the internal field. We propose that such reduction of the field can be obtained by including a metamorphic InGaN layer below the multiple quantum well active region. © 2013 AIP Publishing LLC.

SA Cripps, TJC Hosea, SJ Sweeney, D Lock, T Leinonen, J Lyytikainen, M Dumitrescu (2005)High temperature operation of 760 nm vertical-cavity surface-emitting lasers investigated using photomodulated reflectance wafer measurements and temperature-dependent device studies, In: IEE PROCEEDINGS-OPTOELECTRONICS152(2)pp. 103-109 IEE-INST ELEC ENG
SR Jin, SJ Sweeney, CN Ahmad, AR Adams, BN Murdin (2004)Radiative and Auger recombination in 1.3 mu m InGaAsP and 1.5 mu m InGaAs quantum-well lasers measured under high pressure at low and room temperatures, In: APPLIED PHYSICS LETTERS85(3)pp. 357-359 AMER INST PHYSICS
G Blume, TJC Hosea, SJ Sweeney, P de Mierry, D Lancefield (2005)AlGalnN resonant-cavity LED devices studied by electromodulated reflectance and carrier lifetime techniques, In: IEE PROCEEDINGS-OPTOELECTRONICS152(2)pp. 118-124 IEE-INST ELEC ENG
G Knowles, R Fehse, S Tomic, Stephen Sweeney, TE Sale, Alfred Adams, P O'Reilly, G Steinle, H Riechert (2003)Investigation of 1.3-mu m GaInNAs vertical-cavity surface-emitting lasers (VCSELs) using temperature, high-pressure, and modelling techniques, In: IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS9(5)pp. 1202-1208 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

We have investigated the temperature and pressure dependence of the threshold current (I-th) of 1.3 mum emitting GaInNAs vertical-cavity surface-emitting lasers (VCSELs) and the equivalent edge-emitting laser (EEL) devices employing the same active region. Our measurements show that the VCSEL devices have the peak of the gain spectrum on the high-energy side of the cavity mode energy and hence operate over a wide temperature range. They show particularly promising I-th temperature insensitivity in the 250-350 K range. We have then used a theoretical model based on a 10-band k.P Hamiltonian and experimentally determined recombination coefficients from EELs to calculate the pressure and temperature dependency of I-th. The results show good agreement between the model and the experimental data, supporting both the validity of the model and the recombination rate parameters. We also show that for both device types, the super-exponential temperature dependency of I-th at 350 K and above is due largely to Auger recombination.

G Blume, TJC Hosea, SJ Sweeney, SR Johnson, JB Wang, YH Zhang (2005)Spectroscopic investigations of GaAsSb/GaAs based structures for 1.3 mu m VCSEL applications, In: IEE PROCEEDINGS-OPTOELECTRONICS152(2)pp. 110-117 IEE-INST ELEC ENG
ZL Bushell, P Ludewig, N Knaub, Z Batool, K Hild, W Stolz, SJ Sweeney, K Volz (2014)Growth and characterisation of Ga(NAsSi) alloy by metal-organic vapour phase epitaxy, In: JOURNAL OF CRYSTAL GROWTH396pp. 79-84 ELSEVIER SCIENCE BV
S Buaprathoom, SJ Sweeney, S Pedley (2012)Dual wavelength multiple-angle light scattering system for cryptosporidium detection, In: Progress in Biomedical Optics and Imaging - Proceedings of SPIE8427 Society of Photo-Optical Instrumentation Engineers

A simple, dual wavelength, multiple-angle, light scattering system has been developed for detecting cryptosporidium suspended in water. Cryptosporidium is a coccidial protozoan parasite causing cryptosporidiosis; a diarrheal disease of varying severity. The parasite is transmitted by ingestion of contaminated water, particularly drinking-water, but also accidental ingestion of bathing-water, including swimming pools. It is therefore important to be able to detect these parasites quickly, so that remedial action can be taken to reduce the risk of infection. The proposed system combines multiple-angle scattering detection of a single and two wavelengths, to collect relative wavelength angle-resolved scattering phase functions from tested suspension, and multivariate data analysis techniques to obtain characterizing information of samples under investigation. The system was designed to be simple, portable and inexpensive. It employs two diode lasers (violet InGaN-based and red AlGaInP-based) as light sources and silicon photodiodes as detectors and optical components, all of which are readily available. The measured scattering patterns using the dual wavelength system showed that the relative wavelength angle-resolved scattering pattern of cryptosporidium oocysts was significantly different from other particles (e.g. polystyrene latex sphere, E.coli). The single wavelength set up was applied for cryptosporidium oocysts'size and relative refractive index measurement and differential measurement of the concentration of cryptosporidium oocysts suspended in water and mixed polystyrene latex sphere suspension. The measurement results showed good agreement with the control reference values. These results indicate that the proposed method could potentially be applied to online detection in a water quality control system. © 2012 SPIE.

N Hossain, IP Marko, SR Jin, K Hild, SJ Sweeney, RB Lewis, DA Beaton, T Tiedje (2012)Recombination mechanisms and band alignment of GaAs1-xBix/GaAs light emitting diodes, In: APPLIED PHYSICS LETTERS100(5)ARTN 0pp. ?-? AMER INST PHYSICS
CA Broderick, M Usman, EP O'Reilly, CA Broderick, EP O'Reilly, SJ Sweeney (2012)Band engineering in dilute nitride and bismide semiconductor lasers, In: Semiconductor Science and Technology27(9)

Highly mismatched semiconductor alloys such as GaN As and GaBi As have several novel electronic properties, including a rapid reduction in energy gap with increasing x and also, for GaBiAs, a strong increase in spin-orbit-splitting energy with increasing Bi composition. We review here the electronic structure of such alloys and their consequences for ideal lasers. We then describe the substantial progress made in the demonstration of actual GaInNAs telecommunication (telecom) lasers. These have characteristics comparable to conventional InP-based devices. This includes a strong Auger contribution to the threshold current. We show, however, that the large spin-orbit-splitting energy in GaBiAs and GaBiNAs could lead to the suppression of the dominant Auger recombination loss mechanism, finally opening the route to efficient temperature-stable telecomm and longer wavelength lasers with significantly reduced power consumption. © 2012 IOP Publishing Ltd.

IP Marko, NF Masse, SJ Sweeney, AD Andreev, AR Adams, N Hatori, M Sugawara (2005)Carrier transport and recombination in p-doped and intrinsic 1.3 mu m InAs/GaAs quantum-dot lasers, In: APPLIED PHYSICS LETTERS87(21)ARTN 2pp. ?-? AMER INST PHYSICS

The radiative and nonradiative components of the threshold current in 1.3 mu m, p-doped and undoped quantum-dot semiconductor lasers were studied between 20 and 370 K. The complex behavior can be explained by simply assuming that the radiative recombination and nonradiative Auger recombination rates are strongly modified by thermal redistribution of carriers between the dots. The large differences between the devices arise due to the trapped holes in the p-doped devices. These both greatly increase Auger recombination involving hole excitation at low temperatures and decrease electron thermal escape due to their Coulombic attraction. The model explains the high T-0 values observed near room temperature. (c) 2005 American Institute of Physics.

SJ Sweeney, SR Jin (2013)Bismide-nitride alloys: Promising for efficient light emitting devices in the near- and mid-infrared, In: JOURNAL OF APPLIED PHYSICS113(4)ARTN 0pp. ?-? AMER INST PHYSICS
S Jin, SJ Sweeney (2013)InGaAsBi alloys on InP for efficient near- and mid-infrared light emitting devices, In: JOURNAL OF APPLIED PHYSICS114(21)ARTN 21310 AMER INST PHYSICS
K Hild, SJ Sweeney, S Wright, DA Lock, SR Jin, IP Marko, SR Johnson, SA Chaparro, S-Q Yu, Y-H Zhang (2006)Carrier recombination in 1.3 mu m GaAsSb/GaAs quantum well lasers, In: APPLIED PHYSICS LETTERS89(17)ARTN 1pp. ?-? AMER INST PHYSICS
N Hossain, K Hild, SR Jin, S-Q Yu, SR Johnson, D Ding, Y-H Zhang, SJ Sweeney (2013)The influence of growth conditions on carrier recombination mechanisms in 1.3 mu m GaAsSb/GaAs quantum well lasers, In: APPLIED PHYSICS LETTERS102(4)ARTN 0pp. ?-? AMER INST PHYSICS
MT Crowley, IP Marko, NF Masse, AD Andreev, S Tomic, SJ Sweeney, EP O'Reilly, AR Adams (2009)The Importance of Recombination via Excited States in InAs/GaAs 1.3 mu m Quantum-Dot Lasers, In: IEEE J SEL TOP QUANT15(3)pp. 799-807 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

The temperature dependence of the radiative and nonradiative components of the threshold current density of 1.3 mu m InAs/GaAs quantum-dot lasers have been analyzed both experimentally and theoretically. It is shown that the weak temperature variation measured for the radiative current density arises because the optical matrix element for excited state transitions is significantly smaller than for the ground state transition. In contrast, nonradiative Auger recombination can have a similar probability for transitions involving excited states as for those involving ground state carriers. The sharp increase in the threshold current density at high temperatures follows the temperature variation of the cubed threshold carrier density confirming that Auger recombination is the dominant recombination mechanism in these devices at room temperature.

NF Masse, IP Marko, AR Adams, SJ Sweeney (2009)Temperature insensitive quantum dot lasers: are we really there yet?, In: JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS20pp. 272-276 SPRINGER

Twenty five years ago Arakawa suggested that by confining carriers in three dimensions (in quantum dots) a temperature insensitive threshold current (I-th) could be achieved in semiconductor lasers. In this paper we discuss investigations on state-of-the-art 1.3 mu m InAs/GaAs undoped and p-doped quantum dot lasers for telecommunication applications and discuss the extent to which this original hypothesis has been verified. In this study, the threshold current and its radiative component (I-rad) are measured as a function of temperature and pressure. The results show that although the radiative component of the threshold current can be temperature insensitive in undoped quantum dot lasers, a strong contribution from non-radiative Auger recombination makes the threshold current highly temperature sensitive. We find that p-doped devices can have a temperature insensitive I-th over a limited range around room temperature resulting from an interplay between an increasing non-radiative Auger current and decreasing radiative current. The decrease in I-rad, also observed below 200 K in undoped devices, is attributed to an improvement in the carrier transport with increasing temperature. Gain measurements show that even if p-doping is successful in reducing the effect of gain saturation, the modal net gain of p-doped devices is less than in undoped lasers due to increased non-radiative recombination and non-thermal carrier distribution.

AR Mohmad, F Bastiman, CJ Hunter, R Richards, SJ Sweeney, JS Ng, JPR David (2012)Effects of rapid thermal annealing on GaAs1-xBix alloys, In: APPLIED PHYSICS LETTERS101(1)ARTN 0pp. ?-? AMER INST PHYSICS
SA Sayid, IP Marko, PJ Cannard, X Chen, LJ Rivers, IF Lealman, SJ Sweeney (2010)Thermal Characteristics of 1.55-mu m InGaAlAs Quantum Well Buried Heterostructure Lasers, In: IEEE JOURNAL OF QUANTUM ELECTRONICS46(5)pp. 700-705 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Timothy Eales, Igor Marko, BA Ikyo, Alfred Adams, S Arafin, S Sprengel, M-C Amann, Stephen Sweeney (2017)Wavelength dependence of efficiency limiting mechanisms in Type-I Mid-infrared GaInAsSb/GaSb lasers, In: IEEE Journal of Selected Topics in Quantum Electronics23(6) IEEE

The efficiency limiting mechanisms in type-I GaInAsSb-based quantum well (QW) lasers, emitting at 2.3 μm, 2.6 μm and 2.9 μm, are investigated. Temperature characterization techniques and measurements under hydrostatic pressure identify an Auger process as the dominant non-radiative recombination mechanism in these devices. The results are supplemented with hydrostatic pressure measurements from three additional type-I GaInAsSb lasers, extending the wavelength range under investigation from 1.85-2.90 μm. Under hydrostatic pressure, contributions from the CHCC and CHSH Auger mechanisms to the threshold current density can be investigated separately. A simple model is used to fit the non-radiative component of the threshold current density, identifying the dominance of the different Auger losses across the wavelength range of operation. The CHCC mechanism is shown to be the dominant non-radiative process at longer wavelengths (> 2 μm). At shorter wavelengths (< 2 μm) the CHSH mechanism begins to dominate the threshold current, as the bandgap approaches resonance with the spin-orbit split-off band.

GMT Chai, CA Broderick, EP O'Reilly, Z Othaman, SR Jin, JP Petropoulos, Y Zhong, PB Dongmo, JMO Zide, SJ Sweeney, TJC Hosea (2015)Experimental and modelling study of InGaBiAs/InP alloys with up to 5.8% Bi, and with Delta(so) > E-g, In: SEMICONDUCTOR SCIENCE AND TECHNOLOGY30(9)ARTN 09401 IOP PUBLISHING LTD
EP O'Reilly, SJ Sweeney, S Wang, JMO Zide (2015)Dilute bismides and related alloys Preface, In: SEMICONDUCTOR SCIENCE AND TECHNOLOGY30(9)ARTN 09030 IOP PUBLISHING LTD
JS Ng, WM Soong, MJ Steer, M Hopkinson, JPR David, J Chamings, SJ Sweeney, AR Adams (2007)Long wavelength bulk GaInNAs p-i-n photodiodes lattice matched to GaAs, In: JOURNAL OF APPLIED PHYSICS101(6)ARTN 0pp. ?-? AMER INST PHYSICS

We report bulk GaInNAs p-i-n photodiodes lattice-matched to GaAs substrates, grown by solid source molecular beam epitaxy with photoresponses out to similar to 1.3 mu m. The as-grown samples were characterized optically, structurally, and electrically. A low background doping concentration in the range of 10(14)-10(15) cm(-3) was obtained in the samples. One of the samples with a 0.5 mu m thick GaInNAs absorbing layer gave a responsivity of 0.11 A/W for a band edge of 1.28 mu m at reverse bias of 2 V.

K O'Brien, S J Sweeney, A R Adams, B N Murdin, A Salhi, Y Rouillard, A Joullie (2006)Recombination Processes in Midinfrared InGaAsSb Diode Lasers Emitting at 2.37 mu m, In: Applied Physics Letters89(5)

The temperature dependence of the threshold current of InGaAsSb/AlGaAsSb compressively strained lasers is investigated by analyzing the spontaneous emission from working laser devices through a window formed in the substrate metallization and by applying high pressures. It is found that nonradiative recombination accounts for 80% of the threshold current at room temperature and is responsible for the high temperature sensitivity. The authors suggest that Auger recombination involving hot holes is suppressed in these devices because the spin-orbit splitting energy is larger than the band gap, but other Auger processes persist and are responsible for the low T-0 values.

S R Jin, C N Ahmad, S J Sweeney, A R Adams, B N Murdin, H Page, X Marcadet, C Sirtori, S Tomic (2006)Spectroscopy of GaAs/AlGaAs Quantum-Cascade Lasers Using Hydrostatic Pressure, In: Applied Physics Letters89(22)

The authors have measured the output spectrum and the threshold current in 9.2 mu m wavelength GaAs/Al0.45Ga0.55As quantum-cascade lasers at 115 K as a function of hydrostatic pressure up to 7.3 kbars. By extrapolation back to ambient pressure, thermally activated escape of electrons from the upper lasing state up to delocalized states of the Gamma valley is shown to be an important contribution to the threshold current. On the other hand leakage into the X valley, although it has a very high density of states and is nearly degenerate with the Gamma band edge in the barrier, is insignificant at ambient pressure.

T Thomas, A Mellor, NP Hylton, M Fuehrer, D Alonso-Alvarez, A Braun, NJ Ekins-Daukes, JPR David, SJ Sweeney (2015)Requirements for a GaAsBi 1eV sub-cell in a GaAs-based multi-junction solar cell, In: SEMICONDUCTOR SCIENCE AND TECHNOLOGY30(9)ARTN 09401 IOP PUBLISHING LTD
Stephen V. Kershaw, Stephen Sweeney, Mike T. Harrison, Mike G. Burt (2003)Putting nanocrystals to work: from solutions to devices, In: M. G. Burt, J. H. Harding, A. M. Stoneham (eds.), Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences361(1803)pp. 331-343 The Royal Society

The colloidal route to semiconductor nanocrystals is extremely flexible, with a high degree of control over size, size distribution, surface passivation and internal structure of the nanoparticles. Simple chemically controlled techniques can be used to assemble these particles into dense films or other microscopic structures, suitable for photonic devices. Working with semiconductors or semi-metals which in the bulk form have low or inverted bandgaps, and taking advantage of the blue shift in the quantum confinement regime, nanocrystals can readily be tuned to the infrared wavelengths of interest for telecommunications. Design flexibility is far greater than with conventional compound semiconductors or rare-earth-doped glasses. Preliminary results demonstrating optical gain from II-VI nanocrystal films at room temperature are reported.

Stephen John Sweeney, Konstanze Hild, Shirong Jin (2013)The potential of GaAsBiN for multi-junction solar cells, In: 2013 IEEE 39TH PHOTOVOLTAIC SPECIALISTS CONFERENCE (PVSC)pp. 2474-2478 IEEE

The use of multiple connected absorbing junctions (MJ-solar cells) is currently the best approach to maximize the efficiency of solar cells. Increasing the number of junctions leads to a larger theoretical efficiency. To achieve this requires the development of materials appropriate band gaps, which can be grown to a sufficient thickness to absorb light while current matched to other junctions and at the same time minimizing strain and defect generation by lattice matching. We report on modelling of the quaternary alloy GaAsBiN which has the potential to cover a wide range of band gaps below 1.42eV. In addition, this material can also be grown completely lattice matched onto GaAs or Ge with controllable band offsets which makes it very attractive for solar cell applications.

L. Nattermann, P. Ludewig, N. Knaub, N. W. Rosemann, T. Hepp, E. Sterzer, S. R. Jin, K. Hild, S. Chatterjee, S. J. Sweeney, W. Stolz, K. Volz (2016)MOVPE growth and characterization of quaternary Ga(PAsBi)/GaAs alloys for optoelectronic applications, In: Applied materials today5pp. 209-214 Elsevier

Dilute bismide Ga(PAsBi)-based structures are promising candidates for highly efficient optoelectronic applications, like the 1 eV sub-cell in multi-junction solar cells or the active region in infra-red laser diodes. The band gap can be tuned independently from the lattice constant, which theoretically enables the deposition of lattice-matched layers in a wide range of band gap energies on GaAs substrate. In this work, firstly, the shifts in the band edge positions as a function of composition that are possible with the Ga(PAs(Bi)) alloy were estimated using the virtual crystal approximation and valence band anti-crossing theory. Secondly, systematic investigations on MOVPE growth of Ga(PAsBi) layers are presented. Finally, we show the first photoluminescence activity of quaternary Ga(PAsBi) and compare the experimental results to theory. (C) 2016 Elsevier Ltd. All rights reserved.

Christopher A. Broderick, Wanshu Xiong, Stephen J. Sweeney, Eoin P. O'Reilly, Judy M. Rorison (2016)Dilute bismide alloys grown on GaAs and InP substrates for improved near-and mid-infrared semiconductor lasers, In: 2016 18TH INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS (ICTON)2016-pp. 1-4 IEEE

We present an analysis of dilute bismide quantum well (QW) lasers grown on GaAs and InP substrates. Our theoretical analysis is based upon a 12-band k.p Hamiltonian which directly incorporates the strong impact of Bi incorporation on the band structure using a band-anticrossing approach. For GaBiAs QWs grown on GaAs we analyse the device performance as a function of Bi composition, and quantify the potential to use GaBiAs alloys to realise highly efficient, temperature stable 1.55 mu m lasers. We compare our calculations to measured spontaneous emission (SE) and gain spectra for first-generation GaBiAs lasers and demonstrate quantitative agreement between theory and experiment. We also present a theoretical analysis of InGaBiAs alloys grown on InP substrates. We show that this material system is well suited to the development of mid-infrared lasers, and offers the potential to realise highly efficient InP-based diode lasers incorporating type-I QWs and emitting at > 3 mu m. We quantify the theoretical performance of this new class of mid-infrared lasers, and identify optimised structures for emission across the application-rich 3 - 5 mu m wavelength range. Our results highlight and quantify the potential of dilute bismide alloys to overcome several limitations associated with existing GaAs- and InP-based near-and mid-infrared laser technologies.

I. P. Marko, N. F. Masse, S. J. Sweeney, A. R. Adams, N. Hatori, M. Sugawara (2007)Recombination, transport and loss mechanisms in p-doped InAs/GaAs quantum dots, In: W Jantsch, F Schaffler (eds.), PHYSICS OF SEMICONDUCTORS, PTS A AND B893pp. 837-838 Amer Inst Physics

The results on the temperature dependence of the radiative and non-radiative recombination processes in p-doped and undoped quantum dot (QD) lasers suggest that the observed characteristics of p-doped QDs are caused by an increase in the effective conduction band off-set due to Columbic attraction of the extra holes and so an increased localization of electrons in the dots. This leads to an increase in the temperature at which the carriers are able to establish thermal equilibrium from T=200K in the undoped devices to >= 320K in the p-doped samples. Interestingly this can be used to advantage since, as the temperature increases, the improved efficiency associated with better transport between the dots can be exactly offset by the increasing rate of Auger recombination, thus leading to a temperature stable operation around room temperature.

K. Hild, Sj Sweeney, Sr Jin, Sb Healy, Ep O Rellly, Sr Johnson, J-B Wang, Y-H Zhang, W. Jantsch, F. Schaffler, Stephen Sweeney (2007)Band alignment and carrier recombination in GaAsSb/GaAs quantum wells, In: AIP Conference Proceedings893pp. 1431-1432
Stephen J. Sweeney, Yaping Zhang, Ian D. Goodyer (2012)The development of a novel monolithic spectrometer chip concept, In: J E Broquin, G N Conti (eds.), INTEGRATED OPTICS: DEVICES, MATERIALS, AND TECHNOLOGIES XVI8264(1)pp. 82640O-82640O-13 Spie-Int Soc Optical Engineering

A monolithic, chip-based spectrometer based on the novel concept of a series of electrically addressable high-Q resonators coupled to a ridge waveguide is presented. A discrete monolithic InP-based spectrometer chip has been designed to detect wavelengths spanning a 10nm range in the near-infrared region functioning as a sensor. This spectrometer approach has a number of advantages over traditional spectrometers. As well as being solid state and having no moving parts, the co-location of wavelength dispersion and detection offers advantageous spectral performance in a compact chip form. Optimization of resonator size and composition to detect wavelengths across the spectral range of interest will be discussed together with preliminary experimental results.

Scott Jarvis, Jayanta Mukherjee, Matthew Perren, Stephen J. Sweeney (2013)On the Fundamental Efficiency Limits of Photovoltaic Converters for Optical Power Transfer Applications, In: 2013 IEEE 39TH PHOTOVOLTAIC SPECIALISTS CONFERENCE (PVSC)pp. 1031-1035 IEEE

Dedicated photovoltaic converters for the conversion of monochromatic laser radiation (laser power converters (LPCs)) have been developed for high efficiency conversion of laser radiation at 1550 nm into electrical power. The LPC design is based on the InGaAsP/InP material system and achieves a maximum conversion efficiency of 45 % (+/- 1%) under 1.55 mu m illumination at 1 kW/m(2) at room temperature. We have experimentally mapped out the conversion efficiency of the LPC as a function of temperature (100-300 K) and incident wavelength (tracking the absorber band-edge) in order to investigate the efficiency limiting mechanisms. The LPC achieves a conversion efficiency of 80% (+/- 5 %) at 100 Kelvin, highlighting the importance of various temperature dependent loss mechanisms (radiative-, SRH-, Auger-recombination etc.) which limit the conversion efficiency for photovoltaic converters under normal operation conditions. Here we discuss the experimental results linking them to the various loss mechanisms using a detailed theoretical model and underline important design considerations which should prove useful for developing future high efficiency photovoltaic cells for both solar and laser illumination.

Jayanta Mukherjee, Wolfgang Wulfken, Holger Hartje, Frank Steinsiek, Matthew Perren, Stephen J. Sweeney (2013)Demonstration of eye-safe (1550 nm) terrestrial laser power beaming at 30 m and subsequent conversion into electrical power using dedicated photovoltaics, In: 2013 IEEE 39th Photovoltaic Specialists Conference (PVSC)pp. 1074-1076 IEEE

We report on the successful demonstration of terrestrial laser power beaming across a distance of 30 m at an eye-safe wavelength of 1550 nm. Using novel photovoltaic convertors based on III-V semiconductors an optical to electrical power conversion efficiency of 45±1 % at 1 kW/m 2 and room temperature was achieved. Such an energy delivery system could prove extremely useful as a future energy source specifically in regions and targets where conventional energy delivery systems are un-deployable.

Christopher A. Broderick, Wanshu Xiong, Shirong Jin, Igor P. Marko, Zoe L. Bushell, Konstanze Hild, Peter Ludewig, Wolfgang Stolz, Kerstin Volz, Judy M. Rorison, Stephen J. Sweeney, Eoin P. O'Reilly (2017)Strain-balanced type-II superlattices on GaAs: novel heterostructures for photonics and photovoltaics, In: J Piprek, M Willatzen (eds.), 17TH INTERNATIONAL CONFERENCE ON NUMERICAL SIMULATION OF OPTOELECTRONIC DEVICES NUSOD 2017pp. 115-116 IEEE

We present a theoretical analysis of the optoelectronic properties of type-II GaAs1-xBix/GaNyAs1-y quantum wells (QWs) grown on GaAs substrates. We eludicate the broad scope for band structure engineering in these novel heterostructures, demonstrating that they offer emission and absorption out to mid-infrared wavelengths in structures which can be grown with little or no net strain relative to GaAs. We confirm our analysis by comparing to experiments on a prototype GaAs0.967Bi0.033/GaN0.062As0.938 structure, which show room temperature photoluminescence (PL) and absorption at a wavelength of 1.72 mu m (one of the longest achieved to date from a pseudomorphic GaAs-based heterostructure). Overall, we demonstrate that this new class of type-II QWs has significant promise for (i) extending the wavelength range accessible to the GaAs material platform, and (ii) the development of long-wavelength photonic devices and highly efficient solar cells.

I P Marko, A D Andreev, S J Sweeney, A R Adams, R Krebs, S Deubert, J P Reithmaier, A Forchel (2005)The influence of auger processes on recombination in long-wavelength InAs/GaAs quantum dots, In: J Menendez, C G VanDeWalle (eds.), PHYSICS OF SEMICONDUCTORS, PTS A AND B772pp. 681-682 Amer Inst Physics

Analysis of the temperature dependencies of the threshold current and of the unamplified spontaneous emission in 0.98-mu m and 1.3-mu m In-As/GaAs quantum dot lasers as well as high hydrostatic pressure studies show that the recombination and loss mechanisms are wavelength dependent. The results indicate that the temperature dependence of the threshold current is due to two non-radiative recombination processes. Auger recombination is very important in the 1.3-mu m devices at room temperature and causes their temperature sensitivity. In the 980 nm lasers Auger recombination is negligible, but thermal escape of carriers out of the dots followed by defect related recombination leads to an increase of the threshold current with temperature.

Remi Wache, Marian Florescu, Stephen J. Sweeney, Steven K. Clowes (2015)Selectively reflective transparent sheets, In: G S Subramania, S Foteinopoulou (eds.), ACTIVE PHOTONIC MATERIALS VII9546pp. 954607-954607-10 Spie-Int Soc Optical Engineering

We investigate the possibility to selectively reflect certain wavelengths while maintaining the optical properties on other spectral ranges. This is of particular interest for transparent materials, which for specific applications may require high reflectivity at pre-determined frequencies. Although there exist currently techniques such as coatings to produce selective reflection, this work focuses on new approaches for mass production of polyethylene sheets which incorporate either additives or surface patterning for selective reflection between 8 to 13 mu m. Typical additives used to produce a greenhouse effect in plastics include particles such as clays, silica or hydroxide materials. However, the absorption of thermal radiation is less efficient than the decrease of emissivity as it can be compared with the inclusion of Lambertian materials. Photonic band gap engineering by the periodic structuring of metamaterials is known in nature for producing the vivid bright colors in certain organisms via strong wavelength-selective reflection. Research to artificially engineer such structures has mainly focused on wavelengths in the visible and near infrared. However few studies to date have been carried out to investigate the properties of metastructures in the mid infrared range even though the patterning of microstructure is easier to achieve. We present preliminary results on the diffuse reflectivity using FDTD simulations and analyze the technical feasibility of these approaches.

Benjamin G. Crutchley, Igor P. Marko, Stephen J. Sweeney (2013)The influence of temperature on the recombination processes in blue and green InGaN LEDs, In: Physica status solidi. C10(11)pp. 1533-1536 WILEY-VCH Verlag
Z. L. Bushell, R. M. Joseph, L. Nattermann, P. Ludewig, K. Volz, J. L. Keddie, S. J. Sweeney (2018)Optical functions and critical points of dilute bismide alloys studied by spectroscopic ellipsometry, In: Journal of applied physics123(4) AIP Publishing

Critical point transition energies and optical functions of the novel GaAs-based dilute bismide alloys GaAsBi, GaNAsBi, and GaPAsBi were determined using spectroscopic ellipsometry. The ellipsometry data were analyzed using a parameterized semiconductor model to represent the dielectric function of the alloys as the sum of Gaussian oscillators centered on critical points in the band structure, and from this extracting the energies of those critical points. The band gap and spin-orbit splitting were measured for samples for a range of alloy compositions. The first experimental measurements of the spin-orbit splitting in the GaNAsBi quaternary alloy were obtained, which showed that it is approximately independent of N content, in agreement with theory. The real component of the refractive index in the transparent region below the band gap was found to decrease as the band gap increased for all of the alloys studied, following the usual relations for conventional semiconductors. This work provides key electronic and optical parameters for the development of photonic devices based on these novel alloys. Published by AIP Publishing.

S J Sweeney, D A Lock, A R Adams (2005)Carrier recombination in InGaAs(P) quantum well laser structures: Band gap and temperature dependence, In: J Menendez, C G VanDeWalle (eds.), PHYSICS OF SEMICONDUCTORS, PTS A AND B772pp. 1545-1546 Amer Inst Physics

Using a combination of temperature and pressure dependence measurements, we investigate the relative importance of recombination processes in InGaAs-based QW lasers. We find that radiative and Auger recombination are important in high quality InGaAs material. At 1.5 mu m, Auger recombination accounts for 80% I-th at room temperature reducing to similar to 50% at 1.3 mu m and similar to 15% at 980nm. We also find that Auger recombination dominates the temperature dependence of I-th around room temperature over the entire operating wavelength range studied (980nm-1.5 mu m).

Isabel Helen Balbir Braddock, Maya Al Sid Cheikh, Joydip Ghosh, Roma Eve Mulholland, Joseph Gerard O'Neill, Vlad Stolojan, Carol Crean, Stephen Sweeney, Paul Jonathan Sellin (2022)Formamidinium Lead Halide Perovskite Nanocomposite Scintillators, In: Nanomaterials (Basel, Switzerland)12(13) Mdpi

While there is great demand for effective, affordable radiation detectors in various applications, many commonly used scintillators have major drawbacks. Conventional inorganic scintillators have a fixed emission wavelength and require expensive, high-temperature synthesis; plastic scintillators, while fast, inexpensive, and robust, have low atomic numbers, limiting their X-ray stopping power. Formamidinium lead halide perovskite nanocrystals show promise as scintillators due to their high X-ray attenuation coefficient and bright luminescence. Here, we used a room-temperature, solution-growth method to produce mixed-halide FAPbX(3) (X = Cl, Br) nanocrystals with emission wavelengths that can be varied between 403 and 531 nm via adjustments to the halide ratio. The substitution of bromine for increasing amounts of chlorine resulted in violet emission with faster lifetimes, while larger proportions of bromine resulted in green emission with increased luminescence intensity. By loading FAPbBr(3) nanocrystals into a PVT-based plastic scintillator matrix, we produced 1 mm-thick nanocomposite scintillators, which have brighter luminescence than the PVT-based plastic scintillator alone. While nanocomposites such as these are often opaque due to optical scattering from aggregates of the nanoparticles, we used a surface modification technique to improve transmission through the composites. A composite of FAPbBr(3) nanocrystals encapsulated in inert PMMA produced even stronger luminescence, with intensity 3.8 x greater than a comparative FAPbBr(3)/plastic scintillator composite. However, the luminescence decay time of the FAPbBr(3)/PMMA composite was more than 3 x slower than that of the FAPbBr(3)/plastic scintillator composite. We also demonstrate the potential of these lead halide perovskite nanocomposite scintillators for low-cost X-ray imaging applications.

M. Shkunov, A. N Solodukhin, P. Giannakou, L. Askew , Yu. N Luponosov, D. O Balakirev, N. K Kalinichenko, I. P. Marko, S. J. Sweeney, S. A Ponomarenko (2021)Pixelated full-colour small molecule semiconductor devices towards artificial retinas, In: Journal of Materials Chemistry C Materials for optical and electronic devices9pp. 5858-5867

Opto-stimulation of semiconductor-biointerfaces provides efficient pathways towards eliciting neural activity through selective spectral excitation. In visual prosthesis, tri-colour stimulation capability is the key to restoring full-colour vision. Here we report on investigation of organic photoactive π-conjugated donor–acceptor small molecules based on triphenylamine whose absorption spectra are similar to those of the photoreceptors of the human eye. Photoactive device fabrication and characterisation towards full colour, pixelated retinal prosthesis based on inkjet printing of these molecules is demonstrated, with round pixels reaching 25 microns in diameter. Photo-response is studied via interfacing with biological electrolyte solution and using long-pulse, narrow-band excitation. Both photo-voltage and photo-current responses in the devices with a ZnO hole-blocking interlayer show clear signatures of capacitive charging at the electrolyte/device interface, also demonstrating spectral selectivity comparable to that of human eye’ cones and rods.

C. R. Fitch, G. W. Read, I. P. Marko, D. A. Duffy, L. Cerutti, J.-B. Rodriguez, E. Tournié, S. J. Sweeney (2021)Thermal performance of GaInSb quantum well lasers for silicon photonics applications, In: Applied Physics Letters118(10)101105 American Institute of Physics

A key component for the realization of silicon-photonics is an integrated laser operating in the important communication band near 1.55 μm. One approach is through the use of GaSb-based alloys, which may be grown directly on silicon. In this study, silicon-compatible strained Ga0.8In0.2Sb/Al0.68In0.32Sb composite quantum well (CQW) lasers grown on GaSb substrates emitting at 1.55 μm have been developed and investigated in terms of their thermal performance. Variable temperature and high-pressure techniques were used to investigate the influence of device design on performance. These measurements show that the temperature dependence of the devices is dominated by carrier leakage from the QW region to the Xb minima of the Al0.35Ga0.65As0.03Sb0.97 barrier layers accounting for up to 43% of the threshold current at room temperature. Improvement in device performance may be possible through refinements in the CQW design, while carrier confinement may be improved by optimization of the barrier layer composition. This investigation provides valuable design insights for the monolithic integration of GaSb-based lasers on silicon.

Christopher R. Fitch, Aidas Baltusis, Igor P. Marko, Daehwan Jung, Justin C. Norman, John E. Bowers, Stephen J. Sweeney (2022)Carrier Recombination Properties of Low-Threshold 1.3 μm Quantum Dot Lasers on Silicon, In: IEEE Journal of Selected Topics in Quantum Electronics28(1: Semiconductor Lasers)1900210 Institute of Electrical and Electronics Engineers (IEEE)

On-chip lasers are a key component for the realization of silicon photonics. The performance of silicon-based quantum dot (QD) devices is approaching equivalent QDs on native substrates. To drive forward design optimization we investigated the temperature and pressure dependence of intrinsic and modulation p-doped 1.3 μm InAs dot-in-well (DWELL) laser diodes on on-axis silicon substrates for comparison with devices on GaAs substrates. The silicon-based devices demonstrated low room temperature (RT) threshold current densities ( Jth ) of 192 Acm−2 (538 Acm−2 ) intrinsic (p-doped). Intrinsic devices exhibited temperature stable operation from 170-200 K. Above this, Jth increased more rapidly due to increased non-radiative recombination. P-doping increased the temperature at which Jth(T) started to increase to 300 K with a temperature insensitive region close to RT, but with a higher Jth . A strong correlation was found between the temperature dependence of gain spectrum broadening and the radiative component of threshold Jrad(T) . At low temperature this is consistent with strong inhomogeneous broadening of the carrier distribution, which is more pronounced in the p-doped devices. At higher temperatures Jth increases due to homogeneous thermal broadening coupled with non-radiative recombination. Hydrostatic pressure investigations indicate that while defect-related recombination dominates, radiative and Auger recombination also contribute to Jth .

J Coote, S Reddy, SJ Sweeney (2007)Optimisation of distributed feedback laser biosensors, In: IET OPTOELECTRONICS1(6)pp. 266-271
S Liebich, M Zimprich, P Ludewig, A Beyer, K Volz, W Stolz, B Kunert, N Hossain, SR Jin, SJ Sweeney (2010)MOVPE growth and characterization of Ga(NAsP) laser structures monolithically integrated on Si (001) substrates, In: 22nd IEEE International Semiconductor Laser Conferencepp. 143-144

In this work we focus on the MOVPE growth of Ga(NAsP) laser structures for electrical current injection lattice matched on exactly orientated Si substrates and their structural characterization.

SA Sayid, IP Marko, SJ Sweeney, P Poole (2010)Temperature sensitivity of 1.55μm (100) InAs/InP-based quantum dot lasers, In: Proceedings of 22nd International Conference on Indium Phosphide and Related Materialspp. 23-24

Semiconductor lasers with quantum dot (QD) based active regions have generated a huge amount of interest for applications including communications networks due to their anticipated superior physical properties due to three dimensional carrier confinement. For example, the threshold current of ideal quantum dots is predicted to be temperature insensitive. We have investigated the operating characteristics of 1.55 μm InAs/InP (100) quantum dot lasers focusing on their carrier recombination characteristics using a combination of low temperature and high pressure measurements. By measuring the intrinsic spontaneous emission from a window fabricated in the n-contact of the devices we have measured the radiative component of the threshold current density, Jrad. We find that Jrad is itself relatively temperature insensitive (Fig. 1). However, the total threshold current density, Jth, increases significantly with temperature leading to a characteristic temperature T0~72 K around 220 K-290 K. From this data it is clear that the devices are dominated by a non-radiative recombination process which accounts for up to 94% of the threshold current at room temperature (Fig. 1).

N Hossain, J Chamings, SR Jin, SJ Sweeney, S Liebich, S Reinhard, K Volz, B Kunert, W Stolz (2010)Recombination and loss mechanisms in GaNAsP/GaP QW lasers, In: Proceedings of Photonics Global Conference

In this paper the authors present a comprehensive study of the threshold current and its temperature dependence in novel direct band-gap Ga(NAsP)/GaP QW lasers which provide a potential route to lattice matched monolithic integration of long term stable semiconductor lasers on silicon. It is found that near room temperature, the threshold current is dominated by nonradiative recombination accounting for ~87% of the total threshold current density. A strong increase in threshold current with hydrostatic pressure implies that a carrier leakage path is the dominant carrier recombination mechanism.

SJ Sweeney, Z Batool, K Hild, SR Jin, TJC Hosea (2011)The Potential Role of Bismide Alloys in Future Photonic Devices, In: 13TH INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS

In a similar manner to the dilute nitrides, the incorporation of Bismuth in semiconductors such as GaAs is predicted to lead to a band-anti-crossing effect (in the valence band) causing a large band gap bowing. In addition, the large size of Bismuth atoms gives rise to a large spin-orbit splitting. This opens-up interesting new possibilities for efficient photonic devices, such as near- and mid-infrared lasers which are more thermally stable and less susceptible to losses compared to conventional InP-based devices. Since Bismuth principally influences the valence band, while nitrogen influences the conduction band, combining Bismuth and Nitrogen in III-V alloys offers huge potential for engineering the conduction and valence band offsets, the band gap and spin-orbit splitting, with wide scope for the design of photonic devices.

D Lock, SJ Sweeney, AR Adams, S Deubner, F Klopf, JP Reithmaier, A Forchel (2004)Carrier leakage suppression utilising short-period superlattices in 980 nm InGaAs/GaAs quantum well lasers, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH241(14)pp. 3405-3409
NF Massé, SJ Sweeney, IP Marko, AD Andreev, AR Adams, N Hatori, M Sugawara (2006)Intrinsic limitations of p-doped and undoped 1.3 μm InAs/GaAs quantum dot lasers, In: 20th IEEE International Semi-conductor Laser Conference - Conference Digestpp. 143-144

The temperature dependencies of the recombination and gain processes reveal intrinsic limitations on the performances of quantum dot lasers. Controlling the transport of the carriers using the inhomogeneous broadening makes temperature stable threshold current possible

D Lock, Stephen Sweeney, Alfred Adams (2003)Wavelength dependence of catastrophic optical damage threshold in 980nm semiconductor diode lasers, In: 2003 IEEE LEOS ANNUAL MEETING CONFERENCE PROCEEDINGS, VOLS 1 AND 2pp. 421-422

We investigate the wavelength dependence of the catastrophic optical damage current in 980nm lasers. Using high pressure and low temperature techniques, we find an intrinsic dependence of this threshold on wavelength.

J Chamings, AR Adams, SJ Sweeney, B Kunert, K Volz, W Stolz (2008)Thermal properties of Silicon compatible GaNAsP SQW lasers, In: 2008 IEEE 21ST INTERNATIONAL SEMICONDUCTOR LASER CONFERENCEpp. 61-62
G Blume, TJC Hosea, SJ Sweeney (2005)A study of the low-energy interference oscillations in photoreflectance of GaAsSb/GaAs quantum well structures, In: PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE202(7)pp. 1244-1254
AR Adams, SJ Sweeney (2006)The physics controlling the sensitivity of semiconductor lasers to high temperatures, In: 2006 OPTICAL FIBER COMMUNICATION CONFERENCE/NATIONAL FIBER OPTIC ENGINEERS CONFERENCE, VOLS 1-6pp. 1631-1633
DG McConville, SJ Sweeney, AR Adams, S Tomic, H Riechert (2007)Temperature and pressure dependence of the recombination mechanisms in 1.3 pm and 1.5 pm GaInNAs lasers, In: PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS244(1)pp. 208-212
NE Fox, TK Sharma, SJ Sweeney, TJC Hosea (2009)Room temperature characterisation of InGaAlAs quantum well laser structures using electro-modulated reflectance and surface photovoltage spectroscopy, In: PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE206(5)pp. 796-802
K O'Brien, AR Adams, SJ Sweeney, SR Jin, CN Ahmad, BN Murdin, CL Canedy, I Vurgaftman, JR Meyer (2006)Analysis of the major loss processes in mid-infrared type-II "W" diode lasers, In: Conference Digest - IEEE International Semiconductor Laser Conferencepp. 43-44

The results from high-pressure and low-temperature measurements on mid-infrared type-II W-structure lasers suggest that Auger recombination is the major loss process that prevents their continuous-wave operation at room temperature.

EP O'Reilly, S Fahy, A Lindsay, S Tomić, R Fehse, AR Adams, SJ Sweeney, AD Andreev, PJ Klar, H Grüning, H Riechert (2003)Novel electronic and optoelectronic properties of GaInNAs and related alloys, In: OSA Trends in Optics and Photonics Series88pp. 523-525

We overview how the novel electronic structure of dilute nitride alloys modifies the gain characteristics of GaInNAs lasers. Optimised devices should have comparable or better characteristics than InP-based emitters, enabling GaAs-based 1.3 μm vertical emitting lasers. ©2000 Optical Society of America.

IP Marko, SJ Sweeney, AR Adams, SR Jin, BN Murdin, R Schwertberger, A Somers, JP Reithmaier, A Forchel (2004)Recombination mechanisms in InAs/InP quantum dash lasers studied using high hydrostatic pressure, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH241(14)pp. 3427-3431
IP Marko, AR Adams, SJ Sweeney, R Teissier, AN Baranov, S Tomic (2008)Gamma-L scattering in InAs-based quantum cascade lasers studied using high hydrostatic pressure, In: 2008 IEEE 21ST INTERNATIONAL SEMICONDUCTOR LASER CONFERENCEpp. 47-48
Igor Marko, N Masse, SJ Sweeney, AR Adams, IR Sellers, DJ Mowbray, MS Skolnick, HY Liu, KM Groom (2005)Effect of gain saturation and nonradiative recombination on the thermal characteristics of InAs/GaAs 1.3 mu m quantum dot lasers, In: The 18th Annual Meeting of the IEEE Lasers and Electro-Optics Society, 2005. (LEOS 2005)pp. 401-402 IEEE

Gain saturation increases the radiative component, J(rad), of the threshold current density, J(th), and its contribution to the thermal sensitivity of J(th) in short cavity or low QD density devices. However, the main cause of their thermal sensitivity is a strong non-radiative recombination.

AB Ikyo, IP Marko, AR Adams, SJ Sweeney, A Bachmann, K Kashani-Shirazi, M-C Amann (2009)Gain peak-cavity mode alignment optimisation in buried tunnel junction mid-infrared GaSb vertical cavity surface emitting lasers using hydrostatic pressure, In: IET OPTOELECTRONICS3(6)pp. 305-309
Igor Marko, Alfred Adams, Stephen Sweeney, DJ Mowbray, MS Skolnick, HYY Liu, KM Groom (2005)Recombination and loss mechanisms in low-threshold InAs-GaAs 1.3-mu m quantum-dot lasers, In: IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS11(5)pp. 1041-1047 IEEE

We show that even in quantum-dot (QD) lasers with very low threshold current densities (J(th) = 40-50 A/cm(2) at 300 K), the temperature sensitivity of the threshold current arises from nonradiative recombination that comprises similar to 60% to 70% of J(th) at 300 K, whereas the radiative part of J(th) is almost temperature insensitive. The influence of the nonradiative recombination mechanism decreases with increasing hydrostatic pressure and increasing band gap, which leads to a decrease of the threshold current. We also studied, for the first time, the band gap dependence of the radiative part Of Jth, which in contrast increases strongly with increasing band gap. These results suggest that Auger recombination is an important intrinsic recombination mechanism for 1.3-mu m lasers, even in a very low threshold QD device, and that it is responsible for the temperature sensitivity of the threshold current.

AR Adams, IP Marko, J Mukherjee, SJ Sweeney, A Gocalinska, E Pelucchi, B Corbett (2014)Semiconductor Quantum Well Lasers with a Temperature Insensitive Threshold Current, In: 2014 24TH IEEE INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE (ISLC 2014)pp. 82-83

Quantum well lasers have been extremely successful in a wide range of applications, with optical fibre communications being of particular importance. However, in spite of their success, their performance is not ideal, for example, the threshold current of semiconductor lasers is often very sensitive to temperature. This has led to the need for thermoelectric coolers and associated control electronics to stabilize the laser temperature, however, such coolers often consume more energy than the laser they are controlling and also add to the overall heat dissipation of the system. Such coolers also tend to have far less long-term reliability than the laser diode itself. There are consequently many circumstances where it would be advantageous and far cheaper to simply compensate for temperature variations by mechanisms built into the epitaxial structure of the laser chip itself. This paper focuses on a new design and demonstration of a MQW laser structure which can overcome the intrinsic temperature sensitivity of the laser.

K Hild, Z Batool, SR Jin, N Hossain, IP Marko, TJC Hosea, X Lu, T Tiedje, SJ Sweeney (2013)Auger Recombination Suppression And Band Alignment In GaAsBi/GaAs Heterostructures, In: T Ihn, C Rossler, A Kozikov (eds.), PHYSICS OF SEMICONDUCTORS1566pp. 488-489

Using a combination of experimental and theoretical techniques we present the dependence of the bandgap Eg and the spin orbit splitting energy so, with Bi concentration in GaAsBi/GaAs samples. We find that the concentration at which so,> Eg occurs at 9%. Both spectroscopic as well as first device results indicate a type I alignment.

Konstanze Hild, Stephen Sweeney, DA Lock, S Wright, JB Wang, SR Johnson, YH Zhang (2005)On the thermal stability of 1.3 mu m GaAsSb/GaAs-based lasers, In: 2005 IEEE LEOS Annual Meeting Conference Proceedings (LEOS)pp. 330-331 IEEE

In spite of the almost ideal variation of the radiative current of 1.3 mu m GaAsSb/GaAs-based lasers, the threshold current, J(th), is high due to non-radiative recombination accounting for 90% J(th) near room temperature. This also gives rise to low T-0 values similar to 60K close to room temperature, similar to that for InGaAsP/InP.

K Hild, SJ Sweeney, IP Marko, SR Jin, SR Johnson, SA Chaparro, S Yu, Y-H Zhang (2007)Temperature and pressure dependence of carrier recombination processes in GaAsSb/GaAs quantum well lasers, In: PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS244(1)pp. 197-202
SJ Sweeney, K Hild, IP Marko, S-Q Yu, SR Johnson, Y-H Zhang (2008)Thermal characteristics of 1.3 mu m GaAsSb/GaAs-based Edge- and Surface-emitting Lasers, In: 2008 IEEE 21ST INTERNATIONAL SEMICONDUCTOR LASER CONFERENCEpp. 83-84
SJ Sweeney, IP Marko, SR Jin, K Hild, Z Batool, P Ludewig, L Natterman, Z Bushell, W Stolz, K Volz, CA Broderick, M Usman, PE Harnedy, EP O'Reilly, R Butkute, V Pacebutas, A Geizutis, A Krotkus (2014)Electrically injected GaAsBi Quantum Well Lasers, In: 2014 24TH IEEE INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE (ISLC 2014)pp. 80-81

GaAsBi QWs have the potential to remove inherent recombination losses thereby increasing the efficiency and reducing the temperature sensitivity of near-infrared telecommunications lasers. GaAsBi QW lasers are reported and prospects for 1550nm operation are discussed.

Calibrations of Standard Platinum Resistance Thermometers (SPRTs), the defined interpolating instrument of the International Temperature Scale of 1990 (ITS-90), are performed using fixed-point cells containing nearly pure materials (of the order of 99.9999%). The effect of impurities at the parts per million levels on the measured temperature during fixed point realisations is often the most significant contribution to the calibration uncertainty budget. The recommended method for evaluating this impurity effect relies on chemical analyses whose uncertainties and detection limits are often too large at the small quantities of impurities present, and as such cannot inform a meaningful correction; rather, this result informs the impurity contribution to the uncertainty budget. In order to elucidate the effects of the myriad experimental parameters which may affect the cell conditions, and hence the measured freezing curve, a 2D-axisymmetric coupled heat and impurity transport model utilising the Phase-field Method is developed. A broad qualitative study of tin point realisations illustrates a range of phenomena—including thermal gradient interface instabilities and solid-state de-wetting—which have effects on the measured temperature of the order of 100-200 μK. The interfacial instability has not, to our best knowledge, been predicted elsewhere with respect to the realisation scheme studied. The instability wavelength observed in the model is λ=3.1±0.7 mm, which compares favourably with the growing Fourier mode of shortest wavelength predicted by Mullins-Sekerka instability theory (λ≈4 mm). The solid-state de-wetting phenomenon offers a potential mechanism which agrees well with several experimental trends noted in the literature; the existence of a ‘critical’ film thickness during freeze initiation and the presence of a variable temperature depression over the freeze duration. This work provides a basis for tailoring of experimental techniques so that reliable corrections for the effect of impurities can be determined, thus leveraging a step decrease in potential calibration uncertainties. Since this exercise is performed with the UK national temperature standards, this work directly benefits all fields that rely on the precise measurement of temperature. Also, there is significant potential for further development of the model; some avenues for research are suggested.

I. P. Marko, A. R. Adams, S. J. Sweeney, S. R. Jin, B. N. Murdin, R. Schwertberger, A. Somers, J. P. Reithmaier, A. Forchel (2004)Experimental investigations into the thermal properties of 1.5-1.8-/spl mu/m InAs/InP quantum dash laserspp. 61-62

We present what we believe to be the first ever high-pressure and spontaneous emission measurements on quantum dash lasers. The results show that temperature sensitivity of these lasers is caused by nonradiative processes, which depend on the lasing wavelength.

I P Marko, A R Adams, S J Sweeney, S R Jin, B N Murdin, R Schwertberger, A Somers, J P Reithmaier, A Forchel (2004)Experimental Investigations into the Thermal Properties of 1.5-1.8μm InAs/InP Quantum Dash Lasers, In: 2004 IEEE 19th International Semiconductor Laser Conference, 2004. Conference Digest.

We present what we believe to be the first ever high-pressure and spontaneous emission measurements on quantum dash lasers. The results show that temperature sensitivity of these lasers is caused by nonradiative processes, which depend on the lasing wavelength.

R Fehse, Stephen Sweeney, Alfred Adams, D McConville, H Riechert, L Geelhaar (2004)Influence of growth temperature on defect density in 1.3 mu m GaInNAs-based lasers, In: K Messe (eds.), 2004 IEEE 19TH INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE, CONFERENCE DIGESTpp. 85-86

We show that the dramatic changes in threshold current density with changing active region growth temperature in 1.3mum GaInNAs-based lasers can be attributed nearly entirely to changes in the defect related monomolecular recombination current.

SJ Sweeney, DA Lock, AR Adams, J Menendez, CG VanDeWalle (2005)Carrier recombination in InGaAs(P) quantum well laser structures: Band gap and temperature dependence, In: Physics of Semiconductors, Pts A and B772pp. 1545-1546
N Hossain, K Hild, SR Jin, SJ Sweeney, S-Q Yu, SR Johnson, D Ding, Y-H Zhang (2010)Influence of device structures on carrier recombination in GaAsSb/GaAs QW lasers, In: Proceedings of Photonics Global Conference

We investigate the temperature and pressure dependence of carrier recombination processes occurring in various GaAsSb/GaAs QW laser structures grown under similar growth conditions. Thermally activated carrier leakage via defects is found to be very sensitive to the strain induced interface imperfections. Nonradiative recombination is found to be sensitive to the number of QWs. A strain compensated MQW structure leads to a reduced contribution of non-radiative recombination to the threshold current density (Jth) and a high characteristic temperature (T0) of 73K at room temperature.

IP Marko, AR Adams, SJ Sweeney, NF Masse, R Krebs, JP Reithmaier, A Forchel, DJ Mowbray, MS Skolnick, HY Liu, KM Groom, N Hatori, M Sugawara (2007)Band gap dependence of the recombination processes in InAs/GaAs quantum dots studied using hydrostatic pressure, In: PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS244(1)pp. 82-86
IP Marko, AR Adams, SJ Sweeney, R Teissier, AN Baranov, S Tomic (2009)Evidence of carrier leakage into the L-valley in InAs-based quantum cascade lasers under high hydrostatic pressure, In: PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS246(3)pp. 512-515
Igor Marko, Alfred Adams, Stephen Sweeney, IR Sellers, DJ Mowbray, MS Skolnick, HY Liu, KM Groom (2004)Recombination and loss mechanisms in low-threshold InAs/GaAs 1.3 mu m quantum dot lasers, In: K Messe (eds.), 2004 IEEE 19TH INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE, CONFERENCE DIGESTpp. 57-58

We show that even in quantum dot lasers with very low threshold current density (Jth=740-50 A/cm(2) at 300 K) the temperature sensitivity of the threshold current arises from nonradiative recombination which comprises similar to60-70% of Jth at 300 K.

JS Ng, SL Tan, YL Goh, CH Tan, JPR David, J Allam, SJ Sweeney, AR Adams (2010)InGaAsN as absorber in APDs for 1.3 micron wavelength applicationspp. 187-190

Two issues with using InGaAsN as absorber in avalanche photodiodes (APDs) for 1310nm wavelength applications are addressed here. Firstly, we demonstrated InGaAsN p-i-n diodes with stable photoresponse around 1310nm but reverse leakage current density slightly above the acceptable limit of ~0.2mA/cm2 at 150kV/cm. We also investigated whether or not InGaAsN as absorber is compatible with Al0.8Ga0.2As (the proposed avalanche material in our separate-absorption-multiplication APD design) in terms of the relationship between α and β in InGaAsN. Our observations suggest α ~ β in InGaAsN, making it compatible with Al0.8Ga0.2As.

SL Tan, LJJ Tan, YL Goh, S Zhang, JS Ng, JPR David, IP Marko, J Allam, SJ Sweeney, AR Adams (2010)Reduction of dark current and unintentional background doping in InGaAsN photodetectors by ex situ annealing, In: Proceedings of SPIE - Posters Session7726

InGaAsN is a promising material system to enable low-cost GaAs-based detectors to operate in the telecommunication spectrum, despite the problems posed by the low growth temperature required for nitrogen incorporation. We demonstrate that InGaAsN p+-i-n+ structures with nominal In and N fraction of 10% and 3.8%, grown by molecular beam epitaxy (MBE) under non-optimal growth conditions, can be optimized by post growth thermal annealing to match the performance of optimally grown structures. We report the findings of an annealing study by comparing the photoluminescence spectra, dark current and background concentration of the as-grown and annealed samples. The dark current of the optimally annealed sample is approximately 2 μA/cm2 at an electric field of 100 kV/cm, and is the lowest reported to date for InGaAsN photodetectors with a cut-off wavelength of 1.3 μm. Evidence of lower unintentional background concentration after annealing at a sufficiently high temperature, is also presented.

IP Marko, NF Masse, SJ Sweeney, AR Adams, N Hatori, M Sugawara, W Jantsch, F Schaffler (2007)Recombination, transport and loss mechanisms in p-doped InAs/GaAs quantum dots, In: Physics of Semiconductors, Pts A and B893pp. 837-838
N Hossain, SR Jin, SJ Sweeney, S-Q Yu, SR Johnson, D Ding, Y-H Zhang (2010)Improved performance of GaAsSb/GaAs SQW lasers, In: Proceedings of SPIE: Materials + Mode-Locking7616

This paper reports the improvements and limitations of MBE grown 1.3μm GaAsSb/GaAs single QW lasers. At room temperature, the devices show a low threshold current density (Jth) of 253 Acm-2, a transparent current density of 98 Acm-2, an internal quantum efficiency of 71%, an optical loss of 18 cm-1 and a characteristic temperature (T0) = 51K. The defect related recombination in these devices is negligible and the primary non-radiative current path has a stronger dependence on the carrier density than the radiative current contributing to ~84% of the threshold current at RT. From high hydrostatic pressure dependent measurements, a slight decrease followed by the strong increase in threshold current with pressure is observed, suggesting that the device performance is limited to both Auger recombination and carrier leakage.

Stephen Sweeney, R Fehse, Alfred Adams, H Riechert (2003)Intrinsic temperature sensitivities of 1.3 mu m GaInNAs/GaAs, InGaAsP/InP and AlGaInAs/InP-based semiconductor lasers, In: 2003 IEEE LEOS ANNUAL MEETING CONFERENCE PROCEEDINGS, VOLS 1 AND 2pp. 39-40 IEEE

The apparent temperature stability of GaInNAs-based lasers is-attributed to significant defect current. By removing this current, GaInNAs devices have a similar temperature dependence to InGaAsP devices whilst AlGaInAs devices are more thermally stable.

D Lock, SJ Sweeney, AR Adams (2003)Fundamental limitations of high power 980nm InGaAs/GaAs pump lasers, In: 2003 IEEE LEOS ANNUAL MEETING CONFERENCE PROCEEDINGS, VOLS 1 AND 2pp. 427-428
Stephen Sweeney, D McConville, SR Jin, CN Ahmad, NF Masse, RX Bouyssou, Alfred Adams, C Hanke (2004)Temperature and wavelength dependence of recombination processes in 1.5 mu m InGaAlAs/InP-based lasers, In: 2004 International Conference on Indium Phosphide and Related Materials, Conference Proceedingspp. 738-741

The improved thermal stability of 1.5 mu m InGaAlAs- compared with InGaAs-based lasers is investigated using a combination of low temperature and high pressure techniques. The results indicate that this is due to lower nonradiative Auger recombination in the InGaAlAs devices because of the higher conduction band offset made possible with the InGaAlAs system which results in a lower hole density in the quantum wells at threshold.

NF Masse, Igor Marko, Stephen Sweeney, Alfred Adams, N Hatori, M Sugarawa (2005)The influence of p-doping on the temperature sensitivity of 1.3 mu m quantum dot lasers, In: 2005 IEEE LEOS Annual Meeting Conference Proceedings (LEOS)pp. 603-604 IEEE

We find that non-radiative recombination plays an important role in p-doped quantum-dot lasers. Along with carrier thermalisation effects, this is responsible for the temperature insensitive operation as observed around room temperature in these lasers.

R Fehse, SJ Sweeney, AR Adams, D McConville, H Riechert, L Geelhaar (2004)Influence of growth temperature on carrier recombination in GaInNAs-based lasers, In: IEE PROCEEDINGS-OPTOELECTRONICS151(5)pp. 447-451
SR Jin, SJ Sweeney, AR Adams, PJA Thijs (2003)Coupling of large optical loss with Auger recombination in 1.3 mu m InGaAsP lasers investigated using hydrostatic pressure, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH235(2)pp. 547-551
WM Soong, JS Ng, MJ Steer, M Hopkinson, JPR David, J Chamings, SJ Sweeney, AR Adams, J Allam (2008)Dark current mechanisms in bulk GaInNAs photodiodes, In: Proccedings of 20th International Conference on Indium Phosphide and Related Materials

We have grown a series of bulk GaInNAs p-i-n diodes and identified some of the dark current mechanisms present in our devices. With a nitrogen composition of ~4 %, the band gap can be reduced to 0.94 eV. We also demonstrate that low dark current density is achievable without compromising the absorption and hence quantum efficiency up to 1.4 mum.

N Hossain, J Hosea, S Liebich, M Zimprich, K Volz, B Kunert, W Stolz, S Sweeney (2013)Band Structure Properties of (BGa)P Semiconductors for Lattice Matched Integration on (001) Silicon, In: T Ihn, C Rossler, A Kozikov (eds.), PHYSICS OF SEMICONDUCTORS1566pp. 47-48
R Fehse, AR Adams, SJ Sweeney, S Tomic, H Reichart, A Ramakrishnan (2003)Carrier recombination processes in MOVPE and MBE grown 1.3 mu m GaInNAs edge emitting lasers, In: SOLID-STATE ELECTRONICS47(3)pp. 501-506
SJ Sweeney, T Higashi, AR Adams, T Uchida, T Fujii (2000)A comparison of AlGaInAs and InGaAsP-based 1.3 mu m semiconductor lasers using high pressure, In: HIGH PRESSURE RESEARCH18(1-6)pp. 49-55
SJ Sweeney, AR Adams, EP O'Reilly, M Silver, PJA Thijs (2000)Effect of auger generated hot-holes on 1.5-μm InGaAs(P)-based quantum well semiconductor lasers, In: Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digestpp. 391-392

Using a combination of experimental and theoretical techniques, the direct-CHSH process, that produces hot-holes, was found to be the most important Auger process in 1.5-μm semiconductor lasers. Results of the study clearly highlight the design implications of both quantum well placement and total waveguide thickness on laser performance.

SJ Sweeney, LJ Lyons, D Lock, AR Adams (2002)Direct measurement of facet temperature up to the melting point and COD in high power 980 nm semiconductor diode lasers, In: Conference Digest - IEEE International Semiconductor Laser Conferencepp. 161-162

The high-energy emission from high power lasers was measured and the facet temperature was extracted. Severe heating was observed up to the onset of catastrophic optical damage (COD). The results showed that under high power operation, the laser facet heat-ups to the melting point of GaAs caused the facet to melt.

SJ Sweeney, SR Jin, R Fehse, AR Adams, T Higashi, H Riechert, PJA Thijs (2002)A comparison of the thermal stability of InGaAsP, AlGaInAs and GaInNAs quantum-well lasers for 1.3 μm operation, In: Conference Digest - IEEE International Semiconductor Laser Conferencepp. 43-44

The thermal stabilities of InGaAsP, AlGaInAs and GaInNAs quantum-well lasers for 1.3 μm operation were compared. The optical properties and temperature characteristics of GaInNAs quantum-well (QW) lasers were investigated. It was found that defect-related non-radiative recombination made a significant contribution to the total threshold current in the GaInNAs system, while the Auger recombination process made an increasingly significant contribution at higher temperatures.

S Tomić, R Fehse, SA Choulis, EP O'Reilly, AR Adams, SJ Sweeney, AD Andreev, TJC Hosea, H Riechert (2002)Experimental and theoretical analysis of the recombination processes in GaInNAs 1.3 μm Lasers, In: Conference Digest - IEEE International Semiconductor Laser Conferencepp. 41-42

The recombination processes in GaInNAs 1.3 μm lasers were analyzed theoretically and experimentally. The threshold current was determined by measuring the light emitted from the lasers. The variation of threshold current with temperature and pressure the for quantum well devices was also studied.

SA Sayid, IP Marko, PJ Cannard, X Chen, LJ Rivers, IF Lealman, SJ Sweeney (2010)Thermal performance of 1.55μm InGaAlAs quantum well buried heterostructure lasers, In: IEEE Proceedings of 22nd International Conference on Indium Phosphide and Related Materialspp. 265-268

We have investigated the threshold current Ith and differential quantum efficiency as the function of temperature in InGaAlAs/InP multiple quantum well (MQWs) buried heterostructure (BH) lasers. We find that the temperature sensitivity of Ith is due to non-radiative recombination which accounts for up to ~80% of Jth at room temperature. Analysis of spontaneous emission emitted from the devices show that the dominant non-radiative recombination process is consistent with Auger recombination. We further show that the above threshold differential internal quantum efficiency, ηi, is ~80% at 20°C remaining stable up to 80°C. In contrast, the internal optical loss, αi, increases from 15 cm-1 at 20°C to 22 cm-1 at 80°C, consistent with inter-valence band absorption (IVBA). This suggests that the decrease in power output at elevated temperatures is associated with both Auger recombination and IVBA.

N Hossain, SR Jin, SJ Sweeney, S Liebich, P Ludewig, M Zimprich, K Volz, B Kunert, W Stolz (2011)Physical properties of monolithically integrated Ga(NAsP)/(BGa)P QW lasers on silicon, In: 8th IEEE International Conference on Group IV Photonicspp. 148-150

This paper reports the lattice matched monolithic integration of novel direct band-gap dilute nitride Ga(NAsP) QW lasers on an (001) silicon substrate using novel (BGa)P strain compensating layer. Lasing operation up to 165K is verified with a threshold current density of 1.6kAcm-2 and a characteristic temperature of 73K for a SQW device, which is a positive step towards a commercial solution for the monolithic integration of long term stable laser diodes on silicon substrates.

P Marko, AR Adams, SJ Sweeney, ND Whitbread, AJ Ward, B Asplin, J Robbins (2007)The influence of carrier density non-pinning on the output power of 1.55 μm lasers at high temperature, In: Optics InfoBase Conference Papers
S Jarvis, J Mukherjee, M Perren, SJ Sweeney (2013)On the Fundamental Efficiency Limits of Photovoltaic Converters for Optical Power Transfer Applications, In: 2013 IEEE 39TH PHOTOVOLTAIC SPECIALISTS CONFERENCE (PVSC)pp. 1031-1035 IEEE
AR Adams, R Fehse, S Tomic, EP O'Reilly, A Andreev, G Knowles, TE Sale, SJ Sweeney, G Steinle, A Ramakrishnan, H Riechert (2002)Characterisation of 1.3pm wavelength GaInNAs/GaAs edge-emitting and vertical-cavity surface-emitting lasers using low-temperature and high-pressure, In: CJ ChangHasnain, YX Xia, K Iga (eds.), APOC 2002: ASIA-PACIFIC OPTICAL AND WIRELESS COMMUNICATIONS; MATERIALS AND DEVICES FOR OPTICAL AND WIRELESS COMMUNICATIONS4905pp. 183-197
SJ Sweeney, K Hild, S Jin (2013)The potential of GaAsBiN for multi-junction solar cells, In: 2013 IEEE 39TH PHOTOVOLTAIC SPECIALISTS CONFERENCE (PVSC)pp. 2474-2478 IEEE
SJ Sweeney, SR Jin, CN Ahmad, AR Adams, BN Murdin (2004)Carrier recombination processes in 1.3 mu m and 1.5 mu m InGaAs(P)-based lasers at cryogenic temperatures and high pressures, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH241(14)pp. 3399-3404
SA Sayid, IP Marko, AR Adams, SJ Sweeney, P Barrios, P Poole (2010)Thermal behavior of 1.55 μm (100) InAs/InP-based quantum dot lasers, In: IEEE Poceeedings of 22nd International Semiconductor Laser Conferencepp. 75-76

Unlike InAs/GaAs quantum dot lasers, in 1.55μm InAs/InP devices, non-radiative recombination dominates device behavior from very low temperature (~40K) and accounts for ~94% of Jth at room temperature with a To of ~72K from 220K-290K.

G Knowles, S Tomic, S Jin, R Fehse, SJ Sweeney, TE Sale, AR Adams (2003)Gain-cavity alignment profiling of 1.3 mu m emitting GaInNAs vertical cavity surface emitting lasers (VCSELs) using high pressure techniques, In: PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS235(2)pp. 480-485
SJ Sweeney, D McConville, NF Masse, RX Bouyssou, AR Adams, CN Ahmad, C Hanke (2004)Temperature and pressure dependence of recombination processes in 1.5 mu m InGaAlAs/InP-based quantum well lasers, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH241(14)pp. 3391-3398
K Hild, SJ Sweeney, SR Jin, SB Healy, EP O'Rellly, SR Johnson, J-B Wang, Y-H Zhang, W Jantsch, F Schaffler (2007)Band alignment and carrier recombination in GaAsSb/GaAs quantum wells, In: Physics of Semiconductors, Pts A and B893pp. 1431-1432
Alfred Adams, Igor Marko, J Mukherjee, Stephen Sweeney, A Gocalinska, E Pelucchi, B Corbett (2014)Semiconductor quantum well lasers with a temperature insensitive threshold current, In: Conference Digest - IEEE International Semiconductor Laser Conferencepp. 82-83
Stephen Sweeney, PJA Thijs (2003)Origin of the high temperature performance degradation of 1.5 mu m InGaAs(P)/InP quantum well lasers, In: 2003 IEEE LEOS ANNUAL MEETING CONFERENCE PROCEEDINGS, VOLS 1 AND 2pp. 977-978 IEEE

High temperature degradation of the efficiency of 1.5pm InGaAs(P) lasers is shown to be due to strong coupling between Auger recombination and internal absorption. This is explained using a simple analytical model.

IP Marko, AD Andreev, SJ Sweeney, AR Adams, R Krebs, S Deubert, JP Reithmaier, A Forchel, J Menendez, CG VanDeWalle (2005)The influence of auger processes on recombination in long-wavelength InAs/GaAs quantum dots, In: Physics of Semiconductors, Pts A and B772pp. 681-682
TE Sale, GC Knowles, SJ Sweeney, A Onischenko, JEF Frost, SM Pinches, J Woodhead (2000)-180 to +80 degrees C CW lasing in visible VCSELs, In: 2000 IEEE 17TH INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE, CONFERENCE DIGESTpp. 15-16 IEEE
D Lock, SJ Sweeney, AR Adams, DJ Robbins (2003)Auger recombination in InGaAs/AlGaAs-based MQW semiconductor lasers emitting at 980 nm, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH235(2)pp. 542-546
T Higashi, SJ Sweeney, AF Phillips, AR Adams, EP O'Reilly, T Uchida, T Fujii (1998)Observation of reduced non-radiative recombination current in 1.3-μm AlGaInAs/InP multiple-quantum-well lasers, In: Conference Digest - IEEE International Semiconductor Laser Conferencepp. 61-62

We investigated experimentally the temperature dependence of the threshold current in 1.3-μm AlGaInAs/InP MQW lasers, and found that compared with GaInAsP/InP devices the higher characteristic temperature was caused by a reduction of the non-radiative recombination current.

J Mukherjee, W Wulfken, H Hartje, F Steinsiek, M Perren, SJ Sweeney (2013)Demonstration of Eye-Safe (1550 nm) Terrestrial Laser Power Beaming at 30 m and Subsequent Conversion into Electrical Power Using Dedicated Photovoltaics, In: 2013 IEEE 39TH PHOTOVOLTAIC SPECIALISTS CONFERENCE (PVSC)pp. 1074-1076 IEEE
SJ Sweeney, AR Adams, M Silver, EP O'Reilly, JR Watling, AB Walker, PJA Thijs (1999)Dependence of threshold current on QW position and on pressure in 1.5 mu m InGaAs(P) lasers, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH211(1)pp. 525-531
AR Adams, M Silver, EP OReilly, B Gonul, AF Phillips, SJ Sweeney, PJA Thijs (1996)Hydrostatic pressure dependence of the threshold current in 1.5 mu m strained quantum well lasers, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH198(1)pp. 381-388
SJ Sweeney, AF Phillips, AR Adams, EP O'Reilly, M Silver, PJA Thijs (1998)Transition from radiative to nonradiative recombination in 1.3-μm and 1.5-μm InGaAs(P) multiple quantum well semiconductor diode lasers, In: Conference on Lasers and Electro-Optics Europe - Technical Digestpp. 304-?

Measurements of the threshold current, Ith as a function of temperature, T were performed on 1.3 μm and 1.5 μm compressively strained lasers from 90 K to 370 K and the temperature sensitivity parameter, To. In addition, L, the integrated spontaneous emission emanating from the side of the devices was collected. By measuring L at the threshold as a function of temperature, it was verified that the relationship To(IRad)= T holds true even to above room temperature.

AF Phillips, SJ Sweeney, AR Adams, PJA Thijs (1999)The hydrostatic pressure dependence of the threshold current in 1.3 mu m InGaAsP quantum well semiconductor diode lasers, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH211(1)pp. 513-518
G Knowles, R Fehse, S Tomić, SJ Sweeney, TE Sale, AR Adams, EP O'Reilly, G Steinle, H Riechert (2002)The temperature and pressure dependence of 1.3 μm GaInNAs vertical-cavity surface emitting lasers (VCSELs), In: Conference Digest - IEEE International Semiconductor Laser Conferencepp. 139-140

The temperature and pressure dependence of the threshold current of GaInNAs based vertical-cavity surface-emitting lasers (VCSEL) were studied. The temperature variation of the main recombination processes measured in GaInNAs edge emitting lasers (EEL) was used with the same active regions for calculating the temperature and pressure dependence of the threshold current density of VCSELs. It was shown that the VCSEL has the cavity mode on the low energy side of the gain peak at room temperature by comparing the actual lasing photon energies.

SR Jin, SJ Sweeney, G Knowles, AR Adams, T Higashi, H Riechert, PJA Thijs (2002)Optical investigation of recombination processes in GaInNAs, InGaAsP and AlGaInAs quantum-well lasers using hydrostatic pressure, In: Conference Digest - IEEE International Semiconductor Laser Conferencepp. 83-84

The recombination processes in GaInNAs, InGaAsP and AlGaInAs quantum well lasers were optically investigated using hydrostatic pressure. The lasing- energy dependence of carrier-recombination in these quantum-well lasers were compared. It was found that the defect-related mono-molecular current at threshold remains nearly constant as a function of lasing energy.

D Lock, SJ Sweeney, AR Adams (2004)Pressure induced wavelength dependence of catastrophic optical damage in 980 nm semiconductor diode lasers, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH241(14)pp. 3416-3419
S Sweeney (2017)Optoelectronic Devices
N Hossain, SR Jin, SJ Sweeney, S Liebich, P Ludewig, M Zimprich, B Kunert, K Volz, W Stolz (2010)On the temperature dependence of monolithically integrated Ga(NAsP)/(BGa)P/Si QW lasers, In: Optics InfoBase Conference Papers

Lasing operation up to 120K is reported in novel direct band-gap Ga(NAsP)/(BGa)P lasers grown monolithically on a silicon substrate. A carrier leakage process is found to dominate the temperature dependence of the laser threshold current. © 2010 OSA /FiO/LS 2010.

R Fehse, S Jin, SJ Sweeney, AR Adams, EP O'Reilly, S Illek, AY Egorov, H Riechert (2001)The temperature dependence of the recombination processes in 1.3 mu m GaInNAs-based edge emitting lasers, In: LEOS 2001: 14TH ANNUAL MEETING OF THE IEEE LASERS & ELECTRO-OPTICS SOCIETY, VOLS 1 AND 2, PROCEEDINGSpp. 330-331
SR Jin, SJ Sweeney, AR Adams, T Higashi, H Riechert, PJA Thijs (2003)Wavelength dependence of the modal refractive index in 1.3 mu m InGaAsP, AlGaInAs and GaInNAs lasers using high pressure, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH235(2)pp. 491-495
SJ Sweeney, AF Phillips, AR Adams, EP O'Reilly, PJA Thijs (1998)Determination of the influence of Auger recombination on the threshold current of 1.3 μm and 1.5 μm InGaAs(P) strained-layer lasers and its variation with temperature, In: Conference Digest - IEEE International Semiconductor Laser Conferencepp. 63-64

We investigated the influence of Auger recombination from 90 K to above room temperature and found its contribution to the threshold current at 300 K to be about 80% and 50% at 1.5 μm and at 1.3 μm respectively.

N Hossain, SR Jin, SJ Sweeney, S Liebich, S Reinhard, K Volz, B Kunert, W Stolz (2010)Physical properties of Ga(NAsP)/GaP QW lasers grown by MOVPE, In: 23rd Annual Meeting of the IEEE Photonics Societypp. 65-66

We are reporting for the first time, lasing operation at room temperature (RT) with a low threshold current density (Jth) in novel direct band-gap Ga(NAsP)/GaP QW lasers. A carrier leakage process is found to dominate the temperature dependence of the laser threshold current.

AR Adams, IP Marko, SJ Sweeney, R Teissier, AN Baranov, S Tomić (2009)The effect of hydrostatic pressure on the operation of quantum cascade lasers, In: Proceedings of SPIE - Quantum Cascade Lasers and Applications I7222

Quantum Cascade Lasers (QCLs) have been very successful at long wavelengths, >4μm, and there is now considerable effort to develop QCLs for short wavelength (2-3μm) applications. To optimise both interband and QC lasers it is important to understand the role of radiative and non-radiative processes and their variation with wavelength and temperature. We use high hydrostatic pressure to manipulate the band structure of lasers to identify the dominant efficiency limiting processes. We describe how hydrostatic pressure may also be used to vary the separation between the Γ, Χ and L bands, allowing one to investigate the role of inter-valley carrier scattering on the properties of QCLs. We will describe an example of how pressure can be used to investigate the properties of 2.9-3.3μm InAs/AlSb QCLs. We find that while the threshold current of the 3.3μm devices shows little pressure variation even at room temperature, for the 2.9μm devices the threshold current increases by ~20% over 4kbar at 190K consistent with carrier scattering into the L-minima. Based on our high pressure studies, we conclude that the maximum operating temperature of InAs/AlSb QCLs decreases with decreasing wavelength due to increased carrier scattering into the L-minima of InAs.

SJ Sweeney, SR Jin, S Tomic, AR Adams, T Higashi, H Riechert, PJA Thijs (2003)Hydrostatic pressure dependence of recombination mechanisms in GaInNAs, InGaAsP and AlGaInAs 1.3 mu m quantum well lasers, In: PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS235(2)pp. 474-479
SR Jin, SJ Sweeney, S Tomic, AR Adams, H Riechert (2003)Quantifying pressure-dependent recombination currents in GaInNAs lasers using spontaneous emission measurements, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH235(2)pp. 486-490