Igor Marko

Dr Igor Marko


Research Fellow
PhD
+44 (0)1483 686161
16 ATI 02

Academic and research departments

School of Mathematics and Physics.

About

Research

Research interests

Publications

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 Royal Society of Chemistry

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.

Bowei Li, Yuren Xiang, K.D.G. Imalka Jayawardena, Deying Luo, Zhuo Wang, Xiaoyu Yang, John F. Watts, Steven Hinder, Muhammad T. Sajjad, Thomas Webb, Haitian Luo, Igor Marko, Hui Li, Stuart A.J. Thomson, Rui Zhu, Guosheng Shao, Stephen J. Sweeney, S. Ravi P. Silva, Wei Zhang (2020)Reduced bilateral recombination by functional molecular interface engineering for efficient inverted perovskite solar cells, In: Nano Energy105249 Elsevier

Interface-mediated recombination losses between perovskite and charge transport layers are one of the main reasons that limit the device performance, in particular for the open-circuit voltage (VOC) of perovskite solar cells (PSCs). Here, functional molecular interface engineering (FMIE) is employed to retard the interfacial recombination losses. The FMIE is a facile solution-processed means that introducing functional molecules, the fluorene-based conjugated polyelectrolyte (CPE) and organic halide salt (OHS) on both contacts of the perovskite absorber layer. Through the FMIE, the champion PSCs with an inverted planar heterojunction structure show a remarkable high VOC of 1.18 V whilst maintaining a fill factor (FF) of 0.83, both of which result in improved power conversion efficiencies (PCEs) of 21.33% (with stabilized PCEs of 21.01%). In addition to achieving one of the highest PCEs in the inverted PSCs, the results also highlight the synergistic effect of these two molecules in improving device performance. Therefore, the study provides a straightforward avenue to fabricate highly efficient inverted PSCs.

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.

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.

Igor P Marko, Alfred R Adams, Stephen J Sweeney (2022)Temperature-insensitive InP-based Quantum Well Lasers Operating in the O-band for Datacom Applications, 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 describe the use of a modified QW structure to achieve temperature stability in O-band lasers. We show the potential for temperature insensitivity of threshold from -40 to $+80{\ }^{\circ}\mathrm{C}$ in an InGaAsP/InP structure. Such devices are of interest for lower energy consuming datacomms systems.

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.

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, 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.

BA Ikyo, IP Marko, AR Adams, SJ Sweeney, CL Canedy, I Vurgaftman, CS Kim, M Kim, WW Bewley, JR Meyer (2011)Temperature dependence of 4.1 mu m mid-infrared type II "W" interband cascade lasers, In: APPLIED PHYSICS LETTERS99(2)ARTN 0pp. ?-? AMER INST PHYSICS
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.

IP Marko, AB Ikyo, AR Adams, SJ Sweeney, A Bachmann, K Kashani-Shirazi, M-C Amann (2009)Band-structure and gain-cavity tuning of 2.4-μm GaSb buried tunnel junction VCSELs, In: Proceedings of European Conference on Lasers and Electro-Optics 2009 and the European Quantum Electronics Conference

Low-cost, continuous-wave GaSb-based vertical cavity surface emitting lasers (VCSELs) operating at ~ 2.4 mum up to 50degC have been demonstrated recently. In this work we have used high pressure techniques to investigate ways to improve their performance and extend their working temperature range. Since the band-gap and energy of the gain peak (Ep) increase with pressure at 0.126 meV/MPa at constant temperature, when applied to edge emitting lasers (EEL) we can use pressure to determine the radiative and non-radiative recombination processes occurring. In the VCSEL the pressure dependence of the threshold current, is much more complicated. At the higher temperature the decreasing Auger recombination initially dominates. Therefore we predict that either increasing the band gap or increasing the operating wavelength will allow an improved temperature performance of these GaSb-based VCSELs.

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.

BA Ikyo, IP Marko, K Hild, AR Adams, SJ Sweeney, S Arafin, M-C Amann (2013)The effect of hole leakage and auger recombination on the temperature sensitivity of GaInAsSb/GaSb mid-infrared lasers, In: Lasers and Electro-Optics Europe (CLEO EUROPE/IQEC), 2013 Conference on and International Quantum Electronics Conference
IP Marko, AD Andreev, AR Adams, R Krebs, JP Reithmaier, A Forchel (2003)Auger recombination in 1.3-μm InAs/GaInAs quantum dot lasers studied using high pressure, In: Conference on Lasers and Electro-Optics Europe - Technical Digestpp. 175-175

The Auger recombination in 1.3μm InAs/GalnAs quantum dot lasers were investigated. To analyse the experimental results, theoretical model was used which includes strain, piezoelectric field and electronic structure calculated in the QDs of truncated pyramid shape. It was found that the radiative current increases with pressure, but the Auger recombination current decreases with pressure and is the dominant recombination path at room temperature in 1.3μm QD lasers. © 2003 IEEE.

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 (

Timothy D. Eales, Igor P. Marko, Alf R. Adams, Alexander Andrejew, Kristijonas Vizbaras, Stephen J. Sweeney (2021)Auger Recombination in Mid-Infrared Quantum Well Lasers, In: 2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)pp. 1-1 IEEE

Auger recombination is known to be a significant non-radiative channel in near- and mid-infrared quantum well emitters [1] . As a result, the threshold current density of semiconductor lasers increases substantially with increasing wavelength and temperature, impacting the overall efficiency of a laser-based optoelectronic system. In an Auger process the energy released from an electron-hole recombination is transferred to a third carrier. The one-dimensional confinement of quantum wells and small band offsets (relative to the bandgap) in infrared type-I quantum well geometries permit two fundamentally different categories of Auger mechanisms to operate. We refer to these as activated or thresholdless . In a thresholdless process the absence of an activation energy means that the Auger coefficient of an Auger process varies only weakly with temperature. This contrasts with an activated process where the kinematic threshold causes the Auger coefficient to increase approximately exponentially with temperature. There is no clear consensus in the literature on the nature of Auger recombination in type-I quantum wells, and both have variously been invoked to explain the temperature and wavelength dependence of near- and mid-infrared quantum well lasers [2] , [3] .

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.

Aneirin R. Ellis, Igor P. Marko, Timothy D. Eales, Laurent Cerutti, Marta Rio Calvo, Laura Monge Bartolome, Jean-Baptiste Rodriguez, Eric Tournie, Stephen J. Sweeney (2021)Carrier Recombination Processes in 2.3-mu m Epitaxially Grown Mid-Infrared Laser Diodes on Si(001), In: 27TH INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE (ISLC 2021) IEEE

Epitaxial growth of III-V lasers on CMOS-compatible Si(001) is a key component in the realisation of photonic integrated circuits. In this work we investigate the mechanisms underpinning the performance of first generation GaSb-based devices grown epitaxially on industry-standard Si.

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
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.

I P Marko, A D Andreev, A R Adams, R Krebs, J P Reithmaier, A Forchel (2003)The Role of Auger Recombination in InAs 1.3-/mu m Quantum-Dot Lasers Investigated Using High Hydrostatic Pressure, In: IEEE Journal of Selected Topics in Quantum Electronics9(5) IEEE

InAs quantum-dot (QD) lasers were investigated in the temperature range 20-300 K and under hydrostatic pressure in the range of 0-12 kbar at room temperature. The results indicate that Auger recombination is very important in 1.3-mum QD lasers at room temperature and it is, therefore, the possible cause of the relatively low characteristic temperature observed, of T-0 = 41 K. In the 980-mn QD lasers where T-0 = 110-130 K, radiative recombination dominates. The laser emission photon energy E-las increases linearly with pressure p at 10.1 and 8.3 meV/kbar for 980 nm and 1.3-mum QD lasers, respectively. For the 980-mn QD lasers the threshold current increases with pressure at a rate proportional to the square of the photon energy E-las(2). However, la the threshold current of the 1.3-mum QD laser decreases. by 26% over a 12-kbar pressure range. This demonstrates the presence of a nonradiative recombination contribution to the threshold current, which decreases with increasing pressure. The authors show that this nonradiative contribution is Auger recombination. The results are discussed in the framework of a theoretical model based on the electronic structure and radiative recombination calculations carried out using an 8 x 8 k(.)p Hamiltonian.

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
NF Masse, E Homeyer, IP Marko, AR Adams, SJ Sweeney, O Dehaese, R Piron, F Grillot, S Loualiche (2007)Temperature and pressure dependence of the recombination processes in 1.5 mu m InAs/InP (311)B quantum dot lasers, In: APPL PHYS LETT91(13)131113pp. ?-? AMER INST PHYSICS

The threshold current and its radiative component in 1.5 mu m InAs/InP (311)B quantum dot lasers are measured as a function of the temperature. Despite an almost temperature insensitive radiative current, the threshold current increases steeply with temperature leading to a characteristic temperature T-0 approximate to 55 K around 290 K. Direct observation of spontaneous emission from the wetting layer shows that some leakage from the dots to the wetting layer occurs in these devices. However, a decrease in the threshold current as a function of pressure is also measured suggesting that Auger recombination dominates the nonradiative current and temperature sensitivity of these devices.

IP Marko, ZL Bushell, SR Jin, K Hild, Z Batool, SJ Sweeney, P Ludewig, S Reinhard, L Nattermann, W Stolz, K Volz (2014)Physical properties and optimization of GaBiAs/(Al)GaAs based near-infrared laser diodes grown by MOVPE with up to 4.4% Bi, In: Journal of Physics D: Applied Physics47(34)

This paper reports on progress in the development of GaAsBi/(Al)GaAs based lasers grown using metal-organic vapour phase epitaxy and focuses on the underlying processes governing their efficiency and temperature dependence. Room temperature lasing has been achieved in devices with 2.2% Bi and lasing in devices with 4.4% Bi was observed up to 180 K. We show that the device performance can be improved by optimizing both electrical and optical confinement in the laser structures. Analysis of the temperature dependence of the threshold current together with pure spontaneous emission and high hydrostatic pressure measurements indicate that device performance is currently dominated by non-radiative recombination through defects (>80% of the threshold current at room temperature in 2.2% Bi samples) and that to further improve the device performance and move towards longer wavelengths for optical telecommunications (1.3-1.5 μ m) further effort is required to improve and optimize material quality. © 2014 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.

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.

IP Marko, AD Andreev, AR Adams, R Krebs, JP Reithmaier, A Forchel (2003)Importance of Auger recombination in InAs 1.3 mu m quantum dot lasers, In: ELECTRONICS LETTERS39(1)pp. 58-59 IEE-INST ELEC ENG
I P Marko, A D Andreev, A R Adams, R Krebs, J P Reithmaier, A Forchel (2003)The Importance of Auger Recombination in InAs 1.3 um Quantum Dot Lasers, In: Electronics Letters58(59)

It has been found that Auger recombination is very important in 1.3 μm quantum dot (QD) lasers at room temperature and is the cause of the low characteristic temperature, while in the 980 nm QD lasers radiative recombination dominates.

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.

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.

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.

NF Masse, SJ Sweeney, IP Marko, AR Adams, N Hatori, M Sugawara (2006)Temperature dependence of the gain in p-doped and intrinsic 1.3 mu m InAs/GaAs quantum dot lasers, In: APPL PHYS LETT89(19)191118pp. ?-? AMER INST PHYSICS

The gain of p-doped and intrinsic InAs/GaAs quantum dot lasers is studied at room temperature and at 350 K. Our results show that, although one would theoretically expect a higher gain for a fixed carrier density in p-doped devices, due to the wider nonthermal distribution of carriers amongst the dots at T=293 K, the peak net gain of the p-doped lasers is actually less at low injection than that of the undoped devices. However, at higher current densities, p doping reduces the effect of gain saturation and therefore allows ground-state lasing in shorter cavities and at higher temperatures.

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.

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
IP Marko, Z Batool, K Hild, SR Jin, N Hossain, TJC Hosea, SJ Sweeney, TJC Hosea, JP Petropoulos, Y Zhong, PB Dongmo, JMO Zide (2012)Temperature and Bi-concentration dependence of the bandgap and spin-orbit splitting in InGaBiAs/InP semiconductors for mid-infrared applications, In: Applied Physics Letters101(22)

Replacing small amounts of As with Bi in InGaBiAs/InP induces large decreases and increases in the bandgap, E, and spin-orbit splitting, Δ, respectively. The possibility of achieving Δ > E and a reduced temperature (T) dependence for E are significant for suppressing recombination losses and improving performance in mid-infrared photonic devices. We measure E (x, T) and Δ (x, T) in InGa BiAs/InP samples for 0 x 0.039 by various complementary optical spectroscopic techniques. While we find no clear evidence of a decreased dE/dT (≈0.34 ± 0.06 meV/K in all samples) we find Δ > E for x > 3.3-4.3. The predictions of a valence band anti-crossing model agree well with the measurements. © 2012 American Institute of 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
I Marko, CA Broderick, S Jin, P Ludewig, W Stolz, K Volz, JM Rorison, EP O’Reilly, SJ Sweeney (2016)Optical gain in GaAsBi/GaAs quantum well diode lasers, In: Scientific Reports6 Nature Publishing Group

Electrically pumped GaAsBi/GaAs quantum well lasers are a promising new class of near-infrared devices where, by use of the unusual band structure properties of GaAsBi alloys, it is possible to suppress the dominant energy-consuming Auger recombination and inter-valence band absorption loss mechanisms, which greatly impact upon the device performance. Suppression of these loss mechanisms promises to lead to highly efficient, uncooled operation of telecommunications lasers, making GaAsBi system a strong candidate for the development of next-generation semiconductor lasers. In this report we present the first experimentally measured optical gain, absorption and spontaneous emission spectra for GaAsBi-based quantum well laser structures. We determine internal optical losses of 10–15 cm−1 and a peak modal gain of 24 cm−1, corresponding to a material gain of approximately 1500 cm−1 at a current density of 2 kA cm−2. To complement the experimental studies, a theoretical analysis of the spontaneous emission and optical gain spectra is presented, using a model based upon a 12-band k.p Hamiltonian for GaAsBi alloys. The results of our theoretical calculations are in excellent quantitative agreement with the experimental data, and together provide a powerful predictive capability for use in the design and optimisation of high efficiency lasers in the infrared.

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
NF Masse, SJ Sweeney, IP Marko, AR Adams, N Hatori, M Sugawara (2006)Temperature dependence of the gain in p-doped and intrinsic 1.3 mu m InAs/GaAs quantum dot lasers, In: APPLIED PHYSICS LETTERS89(19)ARTN 1pp. ?-? AMER INST PHYSICS
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.

NF Masse, E Homeyer, IP Marko, AR Adams, SJ Sweeney, O Dehaese, R Piron, F Grillot, S Loualiche (2007)Temperature and pressure dependence of the recombination processes in 1.5 mu m InAs/InP (311)B quantum dot lasers, In: APPLIED PHYSICS LETTERS91(13)ARTN 1pp. ?-? 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.

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.

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.

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.

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
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 .

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).

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.

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.

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.

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.

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.

R Fehse, I Marko, AR Adams (2003)Long wavelength lasers on GaAs substrates, In: IEE PROCEEDINGS-CIRCUITS DEVICES AND SYSTEMS150(6)pp. 521-528
IP Marko, AD Andreev, AR Adams, R Krebs, JP Reithmaier, A Forchel (2003)High-pressure studies of the recombination processes, threshold currents, and lasing wavelengths in InAs/GaInAs quantum dot lasers, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH235(2)pp. 407-411
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
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.

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.

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
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
GZ Mashanovich, WR Headley, MM Milosevic, N Owens, EJ Teo, BQ Xiong, PY Yang, M Nedeljkovic, J Anguita, I Marko, Y Hu (2010)Waveguides for mid-infrared group IV photonics, In: Proceedings of IEEE 7th International Conference on Group IV Photonicspp. 374-376

In this paper we present preliminary work on group IV photonic waveguides that may be suitable for mid-infrared wavelengths. Fabrication and experimental results for two waveguide structures are given.

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.