# Professor Stephen Sweeney

Professor of Physics
PhD BSc CertEd FInstP CPhys FSPIE
+44 (0)1483 689406
12 ATI 01
Centre Secretary: Mrs Nicole Steward
+44 (0)1483 689859

Department of Physics, Advanced Technology Institute, Photonics and Quantum Sciences Group.

### 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
Department of Physics, University of Surrey
2010 - 2015
Advanced Technology Institute, University of Surrey
2009 - 2015
Engineering and Physical Sciences Research Council
01 January 2015 - 31 December 2015
President of the Physics and Astronomy Section
British Science Association

Physics PhD

### Publications

O'Brien K, Sweeney SJ, Adams AR, Murdin BN, Salhi A, Rouillard Y, Joullie A (2006) Recombination processes in midinfrared InGaAsSb diode lasers emitting at 2.37 mu m, APPLIED PHYSICS LETTERS 89 (5) ARTN 051104 AMER INST PHYSICS
Crutchley BG, Marko IP, Pal J, Migliorato MA, Sweeney SJ (2013) Optical properties of InGaN-based LEDs investigated using high hydrostatic pressure dependent techniques, Physica Status Solidi (B) Basic Research 250 (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 (
© 2015 AIP Publishing LLC.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 -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.
Sweeney SJ, Jin SR (2013) Bismide-nitride alloys: Promising for efficient light emitting devices in the near- and mid-infrared, Journal of Applied Physics 113 (4)
GaAsBiN is a potentially interesting alloy which may be exploited in near- and mid-infrared photonic devices. Here we present the predicted band parameters such as band gap (Eg), the spin-orbit splitting energy (SO), band offsets and strain of GaAsBiN on GaAs versus N and Bi compositions based on recent experimental data. We also show how bismuth may be used to form alloys whereby SO > Eg thereby providing a means of suppressing non-radiative CHSH (hot-hole producing) Auger recombination and inter-valence band absorption. We determine the optimum conditions where SO > Eg, which is expected to improve the high-temperature performance and thermal stability of light emitting devices. It is also shown that preferential band offsets are achievable with GaAsBiN, which makes this material system promising for photonic devices operating in the near- and mid-infrared. © 2013 American Institute of Physics.
Marko IP, Batool Z, Hild K, Jin SR, Hossain N, Hosea TJC, Petropoulos JP, Zhong Y, Dongmo PB, Zide JMO, Sweeney SJ (2012) Temperature and Bi-concentration dependence of the bandgap and spin-orbit splitting in InGaBiAs/InP semiconductors for mid-infrared applications, Applied Physics Letters 101 (22)
Replacing small amounts of As with Bi in InGaBiAs/InP induces large decreases and increases in the bandgap, Eg, and spin-orbit splitting, SO, respectively. The possibility of achieving SO > Eg and a reduced temperature (T) dependence for Eg are significant for suppressing recombination losses and improving performance in mid-infrared photonic devices. We measure E g(x, T) and SO (x, T) in In0.53Ga 0.47BixAs1-x/InP samples for 0 x 0.039 by various complementary optical spectroscopic techniques. While we find no clear evidence of a decreased dEg/dT (H0.34 ± 0.06 meV/K in all samples) we find SO > Eg 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.
Adams AR, Marko IP, Sweeney SJ, Teissier R, Baranov AN, Tomi? S (2009) The effect of hydrostatic pressure on the operation of quantum cascade lasers, Proceedings of SPIE - Quantum Cascade Lasers and Applications I 7222 SPIE
Quantum Cascade Lasers (QCLs) have been very successful at long wavelengths, >4¼m, and there is now considerable effort to develop QCLs for short wavelength (2-3¼m) 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 , § 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 2.9-3.3¼m InAs/AlSb QCLs. We find that while the threshold current of the 3.3¼m devices shows little pressure variation even at room temperature, for the 2.9¼m 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.
Ludewig P, Knaub N, Hossain N, Reinhard S, Nattermann L, Marko IP, Jin SR, Hild K, Chatterjee S, Stolz W, Sweeney SJ, Volz K (2013) Electrical injection Ga(AsBi)/(AlGa)As single quantum well laser, Applied Physics Letters 102 (24)
The Ga(AsBi) material system opens opportunities in the field of high efficiency infrared laser diodes. We report on the growth, structural investigations, and lasing properties of dilute bismide Ga(AsBi)/(AlGa)As single quantum well lasers with 2.2% Bi grown by metal organic vapor phase epitaxy on GaAs (001) substrates. Electrically injected laser operation at room temperature is achieved with a threshold current density of 1.56 kA/cm2 at an emission wavelength of
Coote J, Sweeney SJ (2007) Semiconductor lasers as integrated optical biosensors: Sensitivity optimisation, Journal of Physics: Conference Series 76 (1)
Semiconductor lasers contain both a light source and waveguide, rendering them suitable for adaptation to evanescent field biosensing. One-dimensional simulations using the beam propagation method have been carried out for planar semiconductor waveguide structures, with a view to maximising sensitivity of the effective index to changes in the refractive index and thickness of a film on the waveguide surface. Various structural parameters are investigated and it is found that thinning the upper cladding layer maximises the sensitivity. Implications for laser operation are considered, and an optimised structure is proposed. Surface layer index and thickness resolutions of 0.2 and 2nm are predicted. © 2007 IOP Publishing Ltd.
Maspero R, Sweeney SJ, Florescu M (2013) Modelling the Auger Recombination rates of GaAs(1-x)Bi x alloys, 13th International Conference on Numerical Simulation of Optoelectronic Devices, NUSOD 2013 pp. 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
Masse N, Marko I, Sweeney S, Adams AR, Hatori N, Sugarawa M (2005) The influence of p-doping on the temperature sensitivity of 1.3 mu m quantum dot lasers, 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.

Sweeney S, Thijs P (2003) Origin of the high temperature performance degradation of 1.5 mu m InGaAs(P)/InP quantum well lasers, 2003 IEEE LEOS ANNUAL MEETING CONFERENCE PROCEEDINGS, VOLS 1 AND 2 pp. 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.
Sayid SA, Marko IP, Sweeney SJ, Barrios P, Poole PJ (2010) Efficiency limiting processes in 1.55 mu m InAs/InP-based quantum dots lasers, APPLIED PHYSICS LETTERS 97 (16) ARTN 161104 AMER INST PHYSICS
Cheetham KJ, Krier A, Marko IP, Aldukhayel A, Sweeney SJ (2011) Direct evidence for suppression of Auger recombination in GaInAsSbP/InAs mid-infrared light-emitting diodes, APPLIED PHYSICS LETTERS 99 (14) ARTN 141110
Aldukhayel A, Jin SR, Marko IP, Zhang SY, Revin DG, Cockburn JW, Sweeney SJ (2013) Investigations of carrier scattering into L-valley in »=3.5¼m InGaAs/AlAs(Sb) quantum cascade lasers using high hydrostatic pressure, Physica Status Solidi (B) Basic Research 250 (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 (Ith) were undertaken. Using the theoretical optical phonon current (Iph) and carrier leakage (Ileak) 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 Ith with pressure and temperature. It was found that this carrier leakage path accounts for approximately 3% of Ith at RT and is negligible at 100K. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Sweeney SJ, Marko IP, Jin SR, Hild K, Batool Z, Ludewig P, Natterman L, Bushell Z, Stolz W, Volz K, Broderick CA, Usman M, Harnedy PE, Oreilly EP, Butkute R, Pacebutas V, Geiutis A, Krotkus A (2014) Electrically injected GaAsBi quantum well lasers, Conference Digest - IEEE International Semiconductor Laser Conference pp. 80-81
© 2014 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.
Bonmati-Carrion MA, Hild K, Isherwood C, Sweeney SJ, Revell VL, Skene DJ, Rol MA, Madrid JA (2016) Relationship between Human Pupillary Light Reflex and Circadian System Status, PLoS One 11 (9) e0162476 Public Library of Science (PLoS)
Intrinsically photosensitive retinal ganglion cells (ipRGCs), whose photopigment melanopsin
has a peak of sensitivity in the short wavelength range of the spectrum, constitute a common
light input pathway to the olivary pretectal nucleus (OPN), the pupillary light reflex
(PLR) regulatory centre, and to the suprachiasmatic nuclei (SCN), the major pacemaker of
the circadian system. Thus, evaluating PLR under short wavelength light (»max 500 nm)
and creating an integrated PLR parameter, as a possible tool to indirectly assess the status
of the circadian system, becomes of interest. Nine monochromatic, photon-matched light
stimuli (300 s), in 10 nm increments from »max 420 to 500 nm were administered to 15
healthy young participants (8 females), analyzing: i) the PLR; ii) wrist temperature (WT) and
motor activity rhythms (WA), iii) light exposure (L) pattern and iv) diurnal preference (Horne-
Östberg), sleep quality (Pittsburgh) and daytime sleepiness (Epworth). Linear correlations
between the different PLR parameters and circadian status index obtained from WT, WA
and L recordings and scores from questionnaires were calculated. In summary, we found
markers of robust circadian rhythms, namely high stability, reduced fragmentation, high
amplitude, phase advance and low internal desynchronization, were correlated with a
reduced PLR to 460?490 nm wavelengths. Integrated circadian (CSI) and PLR (cp-PLR)
parameters are proposed, that also showed an inverse correlation. These results demonstrate,
for the first time, the existence of a close relationship between the circadian system
robustness and the pupillary reflex response, two non-visual functions primarily under melanopsin-ipRGC
input.
Mohmad AR, Bastiman F, Hunter CJ, Ng JS, Sweeney SJ, David JPR (2011) The effect of Bi composition to the optical quality of GaAs1-xBix, APPLIED PHYSICS LETTERS 99 (4) ARTN 042107 AMER INST PHYSICS
Marko IP, Ludewig P, Bushell ZL, Jin SR, Hild K, Batool Z, Reinhard S, Nattermann L, Stolz W, Volz K, Sweeney SJ (2014) Physical properties and optimization of GaBiAs/(Al)GaAs based near-infrared laser diodes grown by MOVPE with up to 4.4% Bi, Journal of Physics D: Applied Physics 47 (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 ¼ m) further effort is required to improve and optimize material quality. © 2014 IOP Publishing Ltd.
Marko IP, Sweeney SJ, Adams AR, Jin SR, Murdin BN, Schwertberger R, Somers A, Reithmaier JP, Forchel A (2004) Recombination mechanisms in InAs/InP quantum dash lasers studied using high hydrostatic pressure, PHYSICA STATUS SOLIDI B-BASIC RESEARCH 241 (14) pp. 3427-3431 WILEY-V C H VERLAG GMBH
Liebich S, Zimprich M, Beyer A, Lange C, Franzbach DJ, Chatterjee S, Hossain N, Sweeney SJ, Volz K, Kunert B, Stolz W (2011) Laser operation of Ga(NAsP) lattice-matched to (001) silicon substrate, APPLIED PHYSICS LETTERS 99 (7) ARTN 071109 AMER INST PHYSICS
Fehse R, Tomic S, Adams AR, Sweeney SJ, O'Reilly EP, Andreev A, Riechert H (2002) A quantitative study of radiative, Auger, and defect related recombination processes in 1.3-mu m GaInNAs-based quantum-well lasers, IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS 8 (4) pp. 801-810 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Lock D, Sweeney SJ, Adams AR (2004) Pressure induced wavelength dependence of catastrophic optical damage in 980 nm semiconductor diode lasers, PHYSICA STATUS SOLIDI B-BASIC RESEARCH 241 (14) pp. 3416-3419 WILEY-V C H VERLAG GMBH
Hild K, Marko IP, Johnson SR, Yu S-Q, Zhang Y-H, Sweeney SJ (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, APPLIED PHYSICS LETTERS 99 (7) ARTN 071110 AMER INST PHYSICS
Fehse R, Adams AR, Sweeney SJ, Tomic S, Reichart H, Ramakrishnan A (2003) Carrier recombination processes in MOVPE and MBE grown 1.3 mu m GaInNAs edge emitting lasers, SOLID-STATE ELECTRONICS 47 (3) pp. 501-506 PERGAMON-ELSEVIER SCIENCE LTD
Chai GMT, Hosea TJC, Fox NE, Hild K, Ikyo AB, Marko IP, Sweeney SJ, Bachmann A, Arafin S, Amann M-C (2014) Characterization of 2.3 mu m GaInAsSb-based vertical-cavity surface-emitting laser structures using photo-modulated reflectance, JOURNAL OF APPLIED PHYSICS 115 (1) ARTN 013102 AMER INST PHYSICS
Buaprathoom S, Pedley S, Prins AD, Sweeney SJ (2012) High concentration measurement of mixed particle suspensions using simple multi-angle light scattering system, Proceedings of SPIE - The International Society for Optical Engineering 8439
A simple multiple-angle light scattering system was developed for the differential measurement of particle concentrations in suspension even in high concentration where multiple scattering effects are significant based on size. The system combines multiple-angle detection to collect scattered angle dependent light intensities, and Partial Least Square Regression method (PLS-R) to compose the predictive models for analyzing scattered signal obtain concentrations of samples under investigation. The system was designed to be simple, portable and inexpensive. It employs a diode lasers (red AlGaInP-based) as a light source and a silicon photodiode as a detector and optical components, all of which are readily available. The technique was validated using 1.1 ¼m and 3.0¼m polystyrene latex beads in both mono-dispersed and poly-dispersed suspensions. The measurement results showed good agreement between the measured results and reference values. Their deviations from the reference values are 2.4% and 1.5% relating to references' concentrations of 1.3×10 8 and 1.2×10 7 particles/ml for 1.1 ¼m and 3.0 ¼m in mono-dispersed solutions and 2.3 % and 3.5% relating to references' concentrations of 1.1×10 8 and 4.4×10 5 particles/ml for 1.1 ¼m and 3.0 ¼m in mixed solutions, respectively. This system is a compact but high performance system allowing multiple particle sizes in high concentration to be measured simultaneously. © 2012 SPIE.
Tan SL, Soong WM, Green JE, Steer MJ, Zhang S, Tan LJJ, Ng JS, Marko IP, Sweeney SJ, Adams AR, Allam J, David JPR (2013) Experimental evaluation of impact ionization in dilute nitride GaInNAs diodes, Applied Physics Letters 103 (10)
The anomalous behavior of impact ionization in dilute-nitride GaInNAs photodiodes with a range of nitrogen content below 4% is investigated. The ratio of hole- and electron-initiated ionization coefficients, k = ²/±, is enhanced by a factor up to
O'Reilly EP, Fahy S, Lindsay A, Tomi? S, Fehse R, Adams AR, Sweeney SJ, Andreev AD, Klar PJ, Grüning H, Riechert H (2003) Novel electronic and optoelectronic properties of GaInNAs and related alloys, OSA Trends in Optics and Photonics Series 88 pp. 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 ¼m vertical emitting lasers. ©2000 Optical Society of America.
Fehse R, Jin S, Sweeney SJ, Adams AR, O'Reilly EP, Illek S, Egorov AY, Riechert H (2001) The temperature dependence of the recombination processes in 1.3 mu m GaInNAs-based edge emitting lasers, LEOS 2001: 14TH ANNUAL MEETING OF THE IEEE LASERS & ELECTRO-OPTICS SOCIETY, VOLS 1 AND 2, PROCEEDINGS pp. 330-331 IEEE
Hossain N, Hild K, Jin SR, Sweeney SJ, Yu S-Q, Johnson SR, Ding D, Zhang Y-H (2010) Influence of device structures on carrier recombination in GaAsSb/GaAs QW lasers, 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.
Ng JS, Tan SL, Goh YL, Tan CH, David JPR, Allam J, Sweeney SJ, Adams AR (2010) InGaAsN as absorber in APDs for 1.3 micron wavelength applications, pp. 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 ± and ² in InGaAsN. Our observations suggest ± ~ ² in InGaAsN, making it compatible with Al0.8Ga0.2As.
Marko IP, Ikyo AB, Adams AR, Sweeney SJ, Bachmann A, Kashani-Shirazi K, Amann M-C (2009) Band-structure and gain-cavity tuning of 2.4-¼m GaSb buried tunnel junction VCSELs, 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.
Hild K, Sweeney SJ, Marko IP, Jin SR, Johnson SR, Chaparro SA, Yu S, Zhang Y-H (2007) Temperature and pressure dependence of carrier recombination processes in GaAsSb/GaAs quantum well lasers, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 244 (1) pp. 197-202 WILEY-V C H VERLAG GMBH
Sweeney SJ, Jin SR, Tomic S, Adams AR, Higashi T, Riechert H, Thijs PJA (2003) Hydrostatic pressure dependence of recombination mechanisms in GaInNAs, InGaAsP and AlGaInAs 1.3 mu m quantum well lasers, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 235 (2) pp. 474-479 WILEY-V C H VERLAG GMBH
Hossain N, Chamings J, Jin SR, Sweeney SJ, Liebich S, Reinhard S, Volz K, Kunert B, Stolz W (2010) Recombination and loss mechanisms in GaNAsP/GaP QW lasers, 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.
Sweeney SJ, Jha A (2015) Preface, Journal of Physics: Conference Series 619 (1)
Hossain N, Marko IP, Jin SR, Hild K, Sweeney SJ, Lewis RB, Beaton DA, Tiedje T (2012) Recombination mechanisms and band alignment of GaAs1-xBix/GaAs light emitting diodes, APPLIED PHYSICS LETTERS 100 (5) ARTN 051105
Hossain N, Hosea TJC, Sweeney SJ, Liebich S, Zimprich M, Volz K, Kunert B, Stolz W (2011) Band structure properties of novel BxGa1-xP alloys for silicon integration, JOURNAL OF APPLIED PHYSICS 110 (6) ARTN 063101
Cripps SA, Hosea TJC, Sweeney SJ, Lock D, Leinonen T, Lyytikainen J, Dumitrescu M (2005) High temperature operation of 760 nm vertical-cavity surface-emitting lasers investigated using photomodulated reflectance wafer measurements and temperature-dependent device studies, IEE PROCEEDINGS-OPTOELECTRONICS 152 (2) pp. 103-109 IEE-INST ELEC ENG
Sweeney SJ, Higashi T, Andreev A, Adams AR, Uchida T, Fujii T (2001) Superior temperature performance of 1.3 mu m AlGaInAs-Based semiconductor lasers investigated at high pressure and low temperature, PHYSICA STATUS SOLIDI B-BASIC RESEARCH 223 (2) pp. 573-579 WILEY-V C H VERLAG GMBH
Fehse R, Sweeney SJ, Adams AR, O'Reilly EP, Egorov AY, Riechert H, Illek S (2001) Insights into carrier recombination processes in 1.3 mu m GaInNAs-based semiconductor lasers attained using high pressure, ELECTRONICS LETTERS 37 (2) pp. 92-93 IEE-INST ELEC ENG
Fehse R, Sweeney SJ, Adams AR, McConville D, Riechert H, Geelhaar L (2004) Influence of growth temperature on carrier recombination in GaInNAs-based lasers, IEE PROCEEDINGS-OPTOELECTRONICS 151 (5) pp. 447-451 INST ENGINEERING TECHNOLOGY-IET
Marko IP, Adams AR, Sweeney SJ, Teissier R, Baranov AN, Tomic S (2009) Evidence of carrier leakage into the L-valley in InAs-based quantum cascade lasers under high hydrostatic pressure, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 246 (3) pp. 512-515 WILEY-V C H VERLAG GMBH
Hossain N, Jin SR, Sweeney SJ, Liebich S, Ludewig P, Zimprich M, Volz K, Kunert B, Stolz W (2011) Physical properties of monolithically integrated Ga(NAsP)/(BGa)P QW lasers on silicon, 8th IEEE International Conference on Group IV Photonics pp. 148-150 IEEE
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.
Jin SR, Sweeney SJ, Adams AR, Higashi T, Riechert H, Thijs PJA (2003) Wavelength dependence of the modal refractive index in 1.3 mu m InGaAsP, AlGaInAs and GaInNAs lasers using high pressure, PHYSICA STATUS SOLIDI B-BASIC RESEARCH 235 (2) pp. 491-495 WILEY-V C H VERLAG GMBH
Ongrai O, Pearce JV, Machin G, Sweeney SJ (2010) Comparative Study of Pt/Pd and Pt-Rh/Pt Thermocouples, INTERNATIONAL JOURNAL OF THERMOPHYSICS 31 (8-9) pp. 1506-1516 SPRINGER/PLENUM PUBLISHERS
Sweeney SJ, Hild K, Marko IP, Yu S-Q, Johnson SR, Zhang Y-H (2008) Thermal characteristics of 1.3 mu m GaAsSb/GaAs-based Edge- and Surface-emitting Lasers, 2008 IEEE 21ST INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE pp. 83-84 IEEE
Constant SB, Tomic S, Lock D, Sale TE, Sweeney SJ, Hosea TJC (2003) Spectroscopic characterization of 1450 nm semiconductor pump laser structures for Raman amplifiers, JOURNAL OF APPLIED PHYSICS 93 (12) pp. 9446-9455 AMER INST PHYSICS
Marko IP, Adams AR, Sweeney SJ, Whitbread ND, Ward AJ, Asplin B, Robbins DJ (2007) The influence of carrier density non-pinning on the output power of 1.55 ¼m lasers at high temperature, Conference on Lasers and Electro-Optics Europe - Technical Digest
Buaprathoom S, Sweeney SJ, Pedley S (2012) Dual wavelength multiple-angle light scattering system for cryptosporidium detection, Progress in Biomedical Optics and Imaging - Proceedings of SPIE 8427 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.
Bastiman F, Mohmad ARB, Ng JS, David JPR, Sweeney SJ (2012) Non-stoichiometric GaAsBi/GaAs (100) molecular beam epitaxy growth, Journal of Crystal Growth 338 (1) pp. 57-61 Elsevier
The growth of III?V bismuthides is complicated by the low incorporation efficiency of Bi in GaAs, leading either to the formation of metallic Bi droplets or low layer composition fractions. Typically growth is performed between 280 and 350 °C and at near stoichiometric Ga:As fluxes in order to encourage Bi incorporation. However most work reported to date also utilises As2 as the As overpressure constituent. It is found in this work that growth with As4 allows high Bi composition films with the standard 1:20 Ga:As4 beam equivalent pressure ratio (BEPR) utilised for higher temperature buffer layer growth. The Bi fraction versus Bi:As4 BEPR is found to be initially linear, until a maximum value is obtained for a given temperature after which the continued oversupply of Bi results in the formation of droplets.
Sweeney SJ, Knowles G, Sale TE, Adams AR (2001) Quantifying the effect of indirect carrier leakage on visible Al(GaInP) lasers using high pressures and low temperatures, PHYSICA STATUS SOLIDI B-BASIC RESEARCH 223 (2) pp. 567-572 WILEY-V C H VERLAG GMBH
Srinivasan S, Tang Y, Read G, Hossain N, Hang D, Sweeney SJ, Bowers JE (2013) HYBRID SILICON DEVICES FOR ENERGY-EFFICIENT OPTICAL TRANSMITTERS, IEEE MICRO 33 (1) pp. 22-31 IEEE COMPUTER SOC
Blume G, Hosea TJC, Sweeney SJ, de Mierry P, Lancefield D (2005) AlGalnN resonant-cavity LED devices studied by electromodulated reflectance and carrier lifetime techniques, IEE PROCEEDINGS-OPTOELECTRONICS 152 (2) pp. 118-124 IEE-INST ELEC ENG
Sweeney SJ (2004) Novel experimental techniques for semiconductor laser characterisation and optimisation, PHYSICA SCRIPTA T114 pp. 152-158 IOP PUBLISHING LTD
Mukherjee J, Wulfken W, Hartje H, Steinsiek F, Perren M, Sweeney SJ (2013) Demonstration of eye-safe (1550 nm) terrestrial laser power beaming at 30 m and subsequent conversion into electrical power using dedicated photovoltaics, Conference Record of the IEEE Photovoltaic Specialists Conference pp. 1074-1076
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/m2 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. © 2013 IEEE.
Pearce JV, Ongrai O, Machin G, Sweeney SJ (2010) Self-validating thermocouples based on high temperature fixed points, METROLOGIA 47 (1) pp. L1-L3 IOP PUBLISHING LTD
Jin SR, Sweeney SJ, Knowles G, Adams AR, Higashi T, Riechert H, Thijs PJA (2002) Optical investigation of recombination processes in GaInNAs, InGaAsP and AlGaInAs quantum-well lasers using hydrostatic pressure, Conference Digest - IEEE International Semiconductor Laser Conference pp. 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.
Marko IP, Adams AR, Sweeney SJ, Teissier R, Baranov AN, Tomic S (2008) Gamma-L scattering in InAs-based quantum cascade lasers studied using high hydrostatic pressure, 2008 IEEE 21ST INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE pp. 47-48 IEEE
O'Reilly EP, Sweeney SJ, Wang S, Zide JMO (2015) Dilute bismides and related alloys Preface, SEMICONDUCTOR SCIENCE AND TECHNOLOGY 30 (9) ARTN 09030 IOP PUBLISHING LTD
O'Brien K, Adams AR, Sweeney SJ, Jin SR, Ahmad CN, Murdin BN, Canedy CL, Vurgaftman I, Meyer JR (2006) Analysis of the major loss processes in mid-infrared type-II "W" diode lasers, Conference Digest - IEEE International Semiconductor Laser Conference pp. 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. © 2006 IEEE.
Hild K, Sweeney SJ, Jin SR, Healy SB, O'Reilly EP, Johnson SR, Wang JB, Zhang YH (2007) Band alignment and carrier recombination in GaAsSb/GaAs quantum wells, AIP Conference Proceedings 893 pp. 1431-1432
Using a combination of experimental and theoretical techniques, we investigated the band alignment and the carrier recombination processes occurring in GaAsSb/GaAs structures. We find that for Sb fractions
Sweeney SJ (2012) Bismide alloys for photonic devices: Potential and progress, 2012 IEEE Photonics Conference, IPC 2012 pp. 602-603
This paper discusses how the addition of Bismuth to III-V alloys gives rise to improved band structure potentially offering reduced non-radiative losses and improved temperature stability for devices in the near- and mid-infrared. © 2012 IEEE.
Lester LF, Kovanis V, Sze-Chun Chan N, Miyamoto T, Sweeney SJ (2013) Introduction to the issue on semiconductor lasers, IEEE Journal on Selected Topics in Quantum Electronics 19 (4)
Mohmad AR, Bastiman F, Hunter CJ, Richards R, Sweeney SJ, Ng JS, David JPR (2012) Effects of rapid thermal annealing on GaAs1-xBix alloys, APPLIED PHYSICS LETTERS 101 (1) ARTN 012106 AMER INST PHYSICS
Jin SR, Ahmad CN, Sweeney SJ, Adams AR, Murdin BN, Page H, Marcadet X, Sirtori C, Tomic S (2006) Spectroscopy of GaAs/AlGaAs quantum-cascade lasers using hydrostatic pressure, APPLIED PHYSICS LETTERS 89 (22) ARTN 221105 AMER INST PHYSICS
Ng JS, Soong WM, Steer MJ, Hopkinson M, David JPR, Chamings J, Adams AR, Sweeney SJ, Allam J (2007) GaInNAs lattice-matched to GaAs for photodiodes, Conference Proceedings - International Conference on Indium Phosphide and Related Materials pp. 347-349
We present optical and electrical characterization data obtained from bulk GaInNAs (lattice-matched to GaAs) diodes with varying GaInNAs composition. Good lattice-matching to GaAs, low reverse dark current and long wavelength absorption were achieved simultaneously, without the aid of post-growth annealing and use of antimony during the growth. © 2007 IEEE.
Marko I, Sweeney S, Hild K (2016) Temperature stable mid-infrared GaInAsSb/GaSb Vertical Cavity Surface Emitting Lasers (VCSELs), Scientific Reports 6 19595 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 ¼m 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.
Crutchley BG, Marko IP, Sweeney SJ (2013) The influence of temperature on the recombination processes in blue and green InGaN LEDs, Physica Status Solidi (C) Current Topics in Solid State Physics 10 (11) pp. 1533-1536
A temperature dependent investigation into the efficiency droop effect in blue and green InGaN light-emitting diodes (LEDs) is presented. The efficiency droop effect is observed to be the strongest at low temperatures in both blue and green LEDs. We show such behaviour is consistent with a reduced hole injection rate resulting in an increased concentration of electron leakage from the quantum wells. Spectral measurements demonstrate that the emission peak has an "s-shape" dependence on tem-perature and a full-width at half-maximum which increases with decreasing temperature below 100 K. Such observations indicate the importance of carrier localization in the InGaN LEDs. At temperatures where hole injection is not problematic the efficiency droop is the result of carrier delocalization and subsequent defect related recombination with increasing current injection. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Ongrai O, Pearce JV, Machin G, Sweeney SJ (2011) Miniature Co-C eutectic fixed-point cells for self-validating thermocouples, MEASUREMENT SCIENCE AND TECHNOLOGY 22 (1) ARTN 015104 IOP PUBLISHING LTD
Phillips AF, Sweeney SJ, Adams AR, Thijs PJA (1999) The hydrostatic pressure dependence of the threshold current in 1.3 mu m InGaAsP quantum well semiconductor diode lasers, PHYSICA STATUS SOLIDI B-BASIC RESEARCH 211 (1) pp. 513-518 WILEY-V C H VERLAG GMBH
Usman M, Broderick CA, Batool Z, Hild K, Hosea TJC, Sweeney SJ, O'Reilly EP (2013) Impact of alloy disorder on the band structure of compressively strained GaBixAs1-x, PHYSICAL REVIEW B 87 (11) ARTN 115104 AMER PHYSICAL SOC
Hosea TJC, Marko IP, Batool Z, Hild K, Jin SR, Hossain N, Chai GMT, Sweeney SJ, Petropoulos JP, Zhong Y, Dongmo PB, Zide JMO (2012) InGaBiAs/InP semiconductors for mid-infrared applications: Dependence of bandgap and spin-orbit splitting on temperature and bismuth content, ICP 2012 - 3rd International Conference on Photonics 2012, Proceedings pp. 154-158
Replacing small amounts of As with Bi in InGaBiAs/InP induces large decreases and increases in the bandgap, Eg, and spin-orbit splitting, SO, respectively. The possibility of achieving SO>Eg and a reduced temperature (T) dependence for Eg are significant for suppressing recombination losses and improving performance in mid-infrared photonic devices. We measure E g(x, T) and SO(x, T) in In0.53Ga 0.47BixAs1-x/InP samples for 0dxd0.032 by optical spectroscopy. While we find no clear evidence of a decreased dE g/dT (H0.33±0.07meV/K in all samples) we find SO>Eg for x>3.3-4.3%. The predictions of a valence band anti-crossing model agree well with the measurements. © 2012 IEEE.
Tu CW, Odnoblyudov VA, Chamings J, Ahmed S, Sweeney SJ, Keogh DM (2008) Materials and light-emitting diode properties of dilute-nitride GaNP/GaP heterostructures, Device Research Conference - Conference Digest pp. 299-300
In this paper GaNP/GaP LED structures are much simpler to grow than conventional process, chip processing uses existing technology, and GaNP/GaP LEDs exhibit only a small wavelength shift with injection current. With increasing temperature, the electroluminescence (EL) intensity decreases. Thus, GaNP/GaP LEDs are in the process of being commercialized.
Chamings J, Ahmed S, Sweeney SJ, Odnoblyudov VA, Tu CW (2008) Physical properties and efficiency of GaNP light emitting diodes, APPLIED PHYSICS LETTERS 92 (2) ARTN 021101 AMER INST PHYSICS
Blume G, Hild K, Marko IP, Hosea TJC, Yu SQ, Chaparro SA, Samal N, Johnson SR, Zhang YH, Sweeney SJ (2012) Cavity mode gain alignment in GaAsSb-based near-infrared vertical cavity lasers studied by spectroscopy and device measurements, Journal of Applied Physics 112 (3)
We present a combination of spectroscopy and device measurements on GaAsSb/GaAs vertical-cavity surface-emitting laser (VCSEL) structures to determine the temperature at which the wavelength of the VCSEL cavity mode (CM) aligns with that of the quantum well (QW) ground-state transition (GST), and therefore the gain peak. We find that, despite the achievement of room temperature (RT) continuous wave lasing in VCSEL devices, the QW transition and the CM are actually slightly misaligned at this temperature; room temperature electroluminescence measurements from a cleaved edge of the VCSEL wafer indicate that the 300 K QW GST energy is at 0.975 ± 0.005 eV, while the CM measured in the VCSEL surface reflectivity spectra is at 0.9805 ± 0.0002 eV. When the wafer sample is cooled, the CM and QW GST can be brought into alignment at 270 ± 10 K, as confirmed by temperature-dependent electro-modulated reflectance (ER) and edge-electroluminescence spectroscopic studies. This alignment temperature is further confirmed by comparing the temperature dependence of the emission energy of a fabricated VCSEL device with that of an edge-emitting laser structure with a nominally identical active region. The study suggests that for further device improvement, the room temperature CM and QW GST energies should be more closely matched and both designed to a smaller energy of about 0.95 eV, somewhat closer to the 1.31 ¼m target. The study amply demonstrates the usefulness of non-destructive ER characterisation techniques in VCSEL manufacturing with GaAsSb-based QWs. © 2012 American Institute of Physics.
Sweeney SJ, McConville D, Masse NF, Bouyssou RX, Adams AR, Ahmad CN, Hanke C (2004) Temperature and pressure dependence of recombination processes in 1.5 mu m InGaAlAs/InP-based quantum well lasers, PHYSICA STATUS SOLIDI B-BASIC RESEARCH 241 (14) pp. 3391-3398 WILEY-V C H VERLAG GMBH
Fehse R, Jin S, Sweeney SJ, Adams AR, O'Reilly EP, Riechert H, Illek S, Egorov AY (2001) Evidence for large monomolecular recombination contribution to threshold current in 1.3 mu m GaInNAs semiconductor lasers, ELECTRONICS LETTERS 37 (25) pp. 1518-1520 IEE-INST ELEC ENG
Sweeney SJ, Jin SR, Ahmad CN, Adams AR, Murdin BN (2004) Carrier recombination processes in 1.3 mu m and 1.5 mu m InGaAs(P)-based lasers at cryogenic temperatures and high pressures, PHYSICA STATUS SOLIDI B-BASIC RESEARCH 241 (14) pp. 3399-3404 WILEY-V C H VERLAG GMBH
Ikyo BA, Marko IP, Adams AR, Sweeney SJ, Canedy CL, Vurgaftman I, Kim CS, Kim M, Bewley WW, Meyer JR (2011) Temperature dependence of 4.1 mu m mid-infrared type II "W" interband cascade lasers, APPLIED PHYSICS LETTERS 99 (2) ARTN 021102 AMER INST PHYSICS
Thomas T, Mellor A, Hylton NP, Fuehrer M, Alonso-Alvarez D, Braun A, Ekins-Daukes NJ, David JPR, Sweeney SJ (2015) Requirements for a GaAsBi 1eV sub-cell in a GaAs-based multi-junction solar cell, SEMICONDUCTOR SCIENCE AND TECHNOLOGY 30 (9) ARTN 09401 IOP PUBLISHING LTD
Sweeney S (2009) Why not do both?, Physics World 22 (12) pp. 44-45
Crutchley BG, Marko IP, Adams AR, Sweeney SJ (2010) Efficiency limitations of green InGaN LEDs and laser diodes, 22nd IEEE International Semiconductor Laser Conference pp. 27-28
Mukherjee J, Jarvis S, Perren M, Sweeney SJ (2013) Efficiency limits of laser power converters for optical power transfer applications, Journal of Physics D: Applied Physics 46 (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-2) at room temperature. Further design optimization of our LPC is expected to scale the efficiency beyond 50% at 1 kW m-2. © 2013 IOP Publishing Ltd.
Knowles G, Sweeney SJ, Sale TE, Adams AR (2001) Self-heating effects in red (665 nm) VCSELs, IEE PROCEEDINGS-OPTOELECTRONICS 148 (5-6) PII 10.1049/ip-opt:20010843 pp. 256-260 IEE-INST ELEC ENG
Tomi? S, Fehse R, Choulis SA, O'Reilly EP, Adams AR, Sweeney SJ, Andreev AD, Hosea TJC, Riechert H (2002) Experimental and theoretical analysis of the recombination processes in GaInNAs 1.3 ¼m Lasers, Conference Digest - IEEE International Semiconductor Laser Conference pp. 41-42
The recombination processes in GaInNAs 1.3 ¼m 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.
Hossain N, Hild K, Jin SR, Yu SQ, Johnson SR, Ding D, Zhang YH, Sweeney SJ (2013) The influence of growth conditions on carrier recombination mechanisms in 1.3 ¼m GaAsSb/GaAs quantum well lasers, Applied Physics Letters 102 (4)
We investigate the temperature and pressure dependence of the threshold current density of edge-emitting GaAsSb/GaAs quantum well (QW) lasers with different device characteristics. Thermally activated carrier leakage via defects is found to be very sensitive to the growth conditions of GaAsSb QWs. An optimization of the growth conditions reduces the nonradiative recombination mechanisms from 93% to 76% at room temperature. This improvement in carrier recombination mechanisms leads to a large improvement in the threshold current density from 533 Acm-2/QW to 138 Acm-2/QW and the characteristic temperature, T0 (T1), from 51 ± 5 K (104 ± 16 K) to 62 ± 2 K (138 ± 7 K) near room temperature. © 2013 American Institute of Physics.
Marko IP, Andreev AD, Sweeney SJ, Adams AR, Krebs R, Deubert S, Reithmaier JP, Forchel A (2005) The influence of auger processes on recombination in long-wavelength InAs/GaAs quantum dots, Physics of Semiconductors, Pts A and B 772 pp. 681-682 AMER INST PHYSICS
Ongrai O, Pearce JV, Machin G, Sweeney SJ (2010) Comparative Study of Pt/Pd and Pt-Rh/Pt Thermocouples, International Journal of Thermophysics 31 (8-9) pp. 1506-1516 Springer
The Pt/Pd thermocouple has demonstrated superior thermoelectric drift and homogeneity performance over conventional Pt?Rh/Pt thermocouples. Here, we present a systematic comparison of the drift and homogeneity performance of Pt/Pd and Type R thermocouples by ageing the thermocouples at 1350 °C for a total of 500 h and measuring the performance at regular intervals during this time. The thermocouples studied were one Pt/Pd thermocouple, one Type R thermocouple and one ?special? Type R thermocouple which was given the same preparatory annealing treatment as the Pt/Pd thermocouple prior to use. The thermoelectric stability of each thermocouple was measured at the freezing point of Ag (961.78 °C) and the melting point of Co?C eutectic (1324.29 °C). The thermoelectric homogeneity of the thermocouples was also measured. Two difference methods were used by withdrawing the thermocouple from the Ag cell and by moving a localized heat source along the thermocouple. The long-term drift of the Pt/Pd thermocouple was around 50 mK (Ag) and 65 mK (Co?C) after the first 100 h ageing at 1350 °C, followed by a further 25 mK (Ag) and 35 mK (Co?C) over the subsequent 400 h ageing. This drift performance and inhomogeneity were an order of magnitude lower than for the two Type R thermocouples. The Type R thermocouple which was given the ?special? preparatory treatment was about 50 % more stable than the conventional Type R thermocouple.
Lever L, Hu Y, Myronov M, Liu X, Owens N, Gardes FY, Marko IP, Sweeney SJ, Ikoni? Z, Leadley DR, Reed GT, Kelsall RW (2011) Strain engineering of the electroabsorption response in Ge/SiGe multiple quantum well heterostructures, 8th IEEE International Conference on Group IV Photonics pp. 107-108 IEEE
Many fibre-optic telecommunications systems exploit the spectral `window' at 1310 nm, which corresponds to zero dispersion in standard single-mode fibres (SMFs). In particular, several passive optical network (PON) architectures use 1310 nm for upstream signals,1 and so compact, low-cost and low-power modulators operating at 1310 nm that can be integrated into Si electronic-photonic integrated circuits would be extremely desireable for future fibre-to-the-home (FTTH) applications.
Marko IP, Jin SR, Hild K, Batool Z, Bushell ZL, Ludewig P, Stolz W, Volz K, Butkute R, Pacebutas V, Geizutis A, Krotkus A, Sweeney SJ (2015) Properties of hybrid MOVPE/MBE grown GaAsBi/GaAs based near-infrared emitting quantum well lasers, SEMICONDUCTOR SCIENCE AND TECHNOLOGY 30 (9) ARTN 094008 IOP PUBLISHING LTD
Sweeney SJ, Phillips AF, Adams AR, O'Reilly EP, Thijs PJA (1998) The effect of temperature dependent processes on the performance of 1.5-mu m compressively strained InGaAs(P) MQW semiconductor diode lasers, IEEE PHOTONICS TECHNOLOGY LETTERS 10 (8) pp. 1076-1078 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Lock D, Sweeney SJ, Adams AR (2003) Fundamental limitations of high power 980nm InGaAs/GaAs pump lasers, 2003 IEEE LEOS ANNUAL MEETING CONFERENCE PROCEEDINGS, VOLS 1 AND 2 pp. 427-428 IEEE
Mohmad AR, Bastiman F, Hunter CJ, Richards RD, Sweeney SJ, Ng JS, David JPR, Majlis BY (2014) Localization effects and band gap of GaAsBi alloys, Physica Status Solidi (B) Basic Research 251 (6) pp. 1276-1281
The structural and optical properties of GaAs1-xBix alloys for x up to 0.108 have been investigated by high resolution X-ray diffraction and photoluminescence (PL). At room temperature (RT), the PL intensity of the GaAs0.97Bi0.03 sample was found to be ~300 times higher than a GaAs control sample grown at the same temperature (400°C). PL measurements carried out at 10K show that when excitation power, Pex was increased from 0.11 to 1140Wcm-2, the PL peak energy blue-shifts by 80meV while the full-width-at-half-maximum reduces from 115 to 63meV. However, the PL peak emission energy becomes independent of the excitation power at RT. The results indicate the presence of localized energy states in the GaAs0.97Bi0.03 sample, which trap carriers at low temperatures and that the majority of the carriers become delocalized at RT. Furthermore, the temperature dependent PL also shows an S-shape behavior, which is a signature of localization effects. A theoretical model, which was derived by solving a rate equation was employed. The model successfully reproduces the observed S-shape behavior and the theory fits well with the experimental data. The RT band gap of GaAs1-xBix for x up to 0.108 has been plotted and compared with the literature. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Hossain N, Hild K, Jin S, Sweeney SJ, Yu S-Q, Johnson SR, Ding D, Zhang Y-H (2010) Role of growth temperature on the physical characteristics of GaAsSb/GaAs QW lasers, 23rd Annual Meeting of the IEEE Photonics Society pp. 59-60 IEEE
Thermally activated carrier leakage via defects is found to be very sensitive to the growth temperature of GaAsSb quantum wells. Optimization of the growth temperature leads to a low Jth/QW of 138A/cm2 at RT.
Sayid SA, Marko IP, Sweeney SJ, Poole P (2010) Temperature sensitivity of 1.55¼m (100) InAs/InP-based quantum dot lasers, Proceedings of 22nd International Conference on Indium Phosphide and Related Materials pp. 23-24 IEEE
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 ¼m 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).
Lock D, Sweeney SJ, Adams AR, Robbins DJ (2003) Auger recombination in InGaAs/AlGaAs-based MQW semiconductor lasers emitting at 980 nm, PHYSICA STATUS SOLIDI B-BASIC RESEARCH 235 (2) pp. 542-546 WILEY-V C H VERLAG GMBH
Coote J, Reddy S, Sweeney SJ (2009) The development of a compact free spectral range semiconductor laser biosensor, JOURNAL OF THE EUROPEAN OPTICAL SOCIETY-RAPID PUBLICATIONS 4 ARTN 09013 EUROPEAN OPTICAL SOC
Sayid SA, Marko IP, Adams AR, Sweeney SJ, Barrios P, Poole P (2010) Thermal behavior of 1.55 ¼m (100) InAs/InP-based quantum dot lasers, IEEE Poceeedings of 22nd International Semiconductor Laser Conference pp. 75-76
Unlike InAs/GaAs quantum dot lasers, in 1.55¼m 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.
Sweeney SJ, Adams AR, Silver M, O'Reilly EP, Watling JR, Walker AB, Thijs PJA (1999) Dependence of threshold current on QW position and on pressure in 1.5 mu m InGaAs(P) lasers, PHYSICA STATUS SOLIDI B-BASIC RESEARCH 211 (1) pp. 525-531 WILEY-V C H VERLAG GMBH
Jha A, Sweeney SJ (2015) Optical, optoelectronic and photonic materials and applications Preface, SEMICONDUCTOR SCIENCE AND TECHNOLOGY 30 (4) ARTN 04030 IOP PUBLISHING LTD
Kunert B, Liebich S, Zimprich M, Beyer A, Ziegler S, Volz K, Stolz W, Hossain N, Jin SR, Sweeney SJ (2011) Electrical pumped integrated III/V laser lattice-matched to a Silicon substrate, Device Research Conference - Conference Digest, DRC pp. 257-258
The enormous development of Silicon (Si) based integrated circuits (ICs) and micro-electronics is based on the downscaling of semiconductor devices. This driving force, however, is approaching fundamental limitations and therefore new technologies are necessary to guarantee future progress in IC functionalities. © 2011 IEEE.
Hossain N, Jin SR, Sweeney SJ, Liebich S, Ludewig P, Zimprich M, Kunert B, Volz K, Stolz W (2010) On the temperature dependence of monolithically integrated Ga(NAsP)/(BGa)P/Si QW lasers, 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.
Marko IP, Adams AR, Massé NF, Sweeney SJ (2014) Effect of non-pinned carrier density above threshold in InAs quantum dot and quantum dash lasers, IET Optoelectronics 8 (2) pp. 88-93
The impact of carrier density non-pinning above threshold on laser performance is studied in different quantum dot/dash lasers with room temperature emission wavelengths of 0.98-1.52 ¼m. Owing to inhomogeneity in the active region, the non-pinning may be important even above room temperature because of the non-thermal carrier distribution between the dots. This has a large impact on the external differential efficiency and the output power of the devices. In the presence of non-radiative recombination, non-pinning will further decrease the output power and the slope efficiency because of a significant reduction in the number of carriers available for stimulated emission. © The Institution of Engineering and Technology 2014.
Soong WM, Ng JS, Steer MJ, Hopkinson M, David JPR, Chamings J, Sweeney SJ, Adams AR, Allam J (2008) Dark current mechanisms in bulk GaInNAs photodiodes, Proccedings of 20th International Conference on Indium Phosphide and Related Materials IEEE
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.
Jin SR, Sweeney SJ, Ahmad CN, Adams AR, Murdin BN (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, APPLIED PHYSICS LETTERS 85 (3) pp. 357-359 AMER INST PHYSICS
Lever L, Hu Y, Myronov M, Liu X, Owens N, Gardes FY, Marko IP, Sweeney SJ, Ikonic Z, Leadley DR, Reed GT, Kelsall RW (2011) Modulation of the absorption coefficient at 1.3 mu m in Ge/SiGe multiple quantum well heterostructures on silicon, OPTICS LETTERS 36 (21) pp. 4158-4160
We report modulation of the absorption coefficient at 1.3 ¼m in Ge/SiGe multiple quantum well heterostructures on silicon via the quantum-confined Stark effect. Strain engineering was exploited to increase the direct optical bandgap in the Ge quantum wells. We grew 9 nm-thick Ge quantum wells on a relaxed Si0.22Ge0.78 buffer and a contrast in the absorption coefficient of a factor of greater than 3.2 was achieved in the spectral range 1290?1315 nm.
Bushell ZL, Ludewig P, Knaub N, Batool Z, Hild K, Stolz W, Sweeney SJ, Volz K (2014) Growth and characterisation of Ga(NAsSi) alloy by metal-organic vapour phase epitaxy, JOURNAL OF CRYSTAL GROWTH 396 pp. 79-84 ELSEVIER SCIENCE BV
Hunter CJ, Bastiman F, Mohmad AR, Richards R, Ng JS, David JPR, Sweeney SJ (2012) Absorption characteristics of GaAsBi/GaAs diodes in the near-infrared, IEEE Photonics Technology Letters 24 (23) pp. 2191-2194
The absorption properties of a series of GaAsBi /GaAs layers with
Pal J, Migliorato MA, Li CK, Wu YR, Crutchley BG, Marko IP, Sweeney SJ (2013) Enhancement of efficiency of InGaN-based light emitting diodes through strain and piezoelectric field management, Journal of Applied Physics 114 (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.
Reed GT, Thomson DJ, Gardes FY, Hu Y, Owens N, Debnath K, O'Faolain L, Krauss TF, Lever L, Ikonic Z, Kelsall RW, Myronov M, Leadley DR, Marko IP, Sweeney SJ, Cox DC, Brimont A, Sanchis P, Duan GH, Le Liepvre A, Jany C, Lamponi M, Make D, Lelarge F, Fedeli JM, Messaoudene S, Keyvaninia S, Roelkens G, Van Thourhout D, Liu S, Yang X, Petropoulos P (2012) High performance silicon optical modulators, Proceedings of SPIE - The International Society for Optical Engineering 8564
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.
Crutchley BG, Marko IP, Sweeney SJ (2013) The influence of temperature on the recombination processes in blue and green InGaN LEDs, Physica Status Solidi (C) Current Topics in Solid State Physics 2 (12)
A temperature dependent investigation into the efficiency droop effect in blue and green InGaN light-emitting diodes (LEDs) is presented. The efficiency droop effect is observed to be the strongest at low temperatures in both blue and green LEDs. We show such behaviour is consistent with a reduced hole injection rate resulting in an increased concentration of electron leakage from the quantum wells. Spectral measurements demonstrate that the emission peak has an "s-shape" dependence on tem-perature and a full-width at half-maximum which increases with decreasing temperature below 100 K. Such observations indicate the importance of carrier localization in the InGaN LEDs. At temperatures where hole injection is not problematic the efficiency droop is the result of carrier delocalization and subsequent defect related recombination with increasing current injection. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Batool Z, Chatterjee S, Chernikov A, Duzik A, Fritz R, Gogineni C, Hild K, Hosea TJC, Imhof S, Johnson SR, Jiang Z, Jin S, Koch M, Koch SW, Kolata K, Lewis RB, Lu X, Masnadi-Shirazi M, Millunchick JM, Mooney PM, Riordan NA, Rubel O, Sweeney SJ, Thomas JC, Thränhardt A, Tiedje T, Volz K (2013) Bismuth-containing III-V semiconductors: Epitaxial growth and physical properties, pp. 139-158
Sweeney SJ, Batool Z, Hild K, Jin SR, Hosea TJC (2011) The Potential Role of Bismide Alloys in Future Photonic Devices, 13TH INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS IEEE
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.
Rice J, Kershaw SV, Dobson P, Oliver RA, Parker MC, Sweeney SJ (2003) Putting nanocrystals to work: from solutions to devices - Discussion, PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY OF LONDON SERIES A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES 361 (1803) pp. 340-343 ROYAL SOC LONDON
Sweeney SJ, Krause S (2009) Selected Papers from the Second International Conference on Optical, Optoelectronic and Photonic Materials and Applications, 2007, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS 20 pp. 1-2 SPRINGER
Hild K, Batool Z, Jin SR, Hossain N, Marko IP, Hosea TJC, Lu X, Tiedje T, Sweeney SJ (2013) Auger Recombination Suppression And Band Alignment In GaAsBi/GaAs Heterostructures, PHYSICS OF SEMICONDUCTORS 1566 pp. 488-489 AMER INST PHYSICS
Sweeney SJ, Marko IP, Jin SR, Hild K, Batool Z, Ludewig P, Natterman L, Bushell Z, Stolz W, Volz K, Broderick CA, Usman M, Harnedy PE, O'Reilly EP, Butkute R, Pacebutas V, Geizutis A, Krotkus A (2014) Electrically injected GaAsBi Quantum Well Lasers, 2014 24TH IEEE INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE (ISLC 2014) pp. 80-81 IEEE COMPUTER SOC
Ongrai O, Pearce JV, Machin G, Sweeney SJ (2013) Self-calibration of a W/Re thermocouple using a miniature Ru-C (1954 °c) eutectic cell, AIP Conference Proceedings 1552 8 pp. 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.
Tan SL, Hunter CJ, Zhang S, Tan LJJ, Goh YL, Ng JS, David JPR, Marko IP, Sweeney SJ, Adams AR, Allam J (2012) Improved Optoelectronic Properties of Rapid Thermally Annealed Dilute Nitride GaInNAs Photodetectors, Journal of Electronic Materials pp. 1-9
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.
Blume G, Hosea TJC, Sweeney SJ (2005) A study of the low-energy interference oscillations in photoreflectance of GaAsSb/GaAs quantum well structures, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 202 (7) pp. 1244-1254 WILEY-V C H VERLAG GMBH
Jarvis S, Mukherjee J, Perren M, Sweeney SJ (2013) On the fundamental efficiency limits of photovoltaic converters for optical power transfer applications, Conference Record of the IEEE Photovoltaic Specialists Conference pp. 1031-1035
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 ¼m illumination at 1 kW/m2 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. © 2013 IEEE.
Adams AR, Sweeney SJ (2006) The physics controlling the sensitivity of semiconductor lasers to high temperatures, 2006 OPTICAL FIBER COMMUNICATION CONFERENCE/NATIONAL FIBER OPTIC ENGINEERS CONFERENCE, VOLS 1-6 pp. 1631-1633 OPTICAL SOC AMERICA
Jin SR, Sweeney SJ, Tomic S, Adams AR, Riechert H (2003) Unusual increase of the Auger recombination current in 1.3 mu m GaInNAs quantum-well lasers under high pressure, APPLIED PHYSICS LETTERS 82 (14) pp. 2335-2337 AMER INST PHYSICS
Lock DA, Hall SRG, Prins AD, Crutchley BG, Kynaston S, Sweeney SJ (2013) LED junction temperature measurement using generated photocurrent, IEEE/OSA Journal of Display Technology 9 (5) pp. 396-401
LED-based lamps that are currently on the market are expensive due to the complex packaging required to dissipate the heat generated. This also limits their performance and lifetime due to the degradation of the phosphor or individual LED chips, in the case of RGB sources. There is a strong commercial imperative to develop in situ technology to measure and ultimately compensate for the thermal environment of a luminaire. © 2005-2012 IEEE.
Hossain N, Jin SR, Liebich S, Zimprich M, Volz K, Kunert B, Stolz W, Sweeney SJ (2012) Efficiency-limiting processes in Ga(NAsP)/GaP quantum well lasers, APPLIED PHYSICS LETTERS 101 (1) ARTN 011107 AMER INST PHYSICS
Jin SR, Sweeney SJ, Adams AR, Thijs PJA (2003) Coupling of large optical loss with Auger recombination in 1.3 mu m InGaAsP lasers investigated using hydrostatic pressure, PHYSICA STATUS SOLIDI B-BASIC RESEARCH 235 (2) pp. 547-551 WILEY-V C H VERLAG GMBH
Bastiman F, Cullis AG, David JPR, Sweeney SJ (2012) Bi incorporation in GaAs(100)-2×1 and 4×3 reconstructions investigated by RHEED and STM, Journal of Crystal Growth 341 (1) pp. 19-23 Elsevier
Bi acts as a surfactant in molecular beam epitaxy (MBE) growth on GaAs(100). Incorporation is achieved by disequilibrium at growth temperatures below
Blume G, Hosea TJC, Sweeney SJ, Johnson SR, Wang JB, Zhang YH (2005) Spectroscopic investigations of GaAsSb/GaAs based structures for 1.3 mu m VCSEL applications, IEE PROCEEDINGS-OPTOELECTRONICS 152 (2) pp. 110-117 IEE-INST ELEC ENG
Wache R, Florescu M, Sweeney SJ, Clowes SK (2015) Selectively reflective transparent sheets, ACTIVE PHOTONIC MATERIALS VII 9546 SPIE-INT SOC OPTICAL ENGINEERING
Sweeney S (2011) Selected papers from the Semiconductor and Integrated Optoelectronics (SIOE'10) Conference, IET OPTOELECTRONICS 5 (3) pp. 99-99 INST ENGINEERING TECHNOLOGY-IET
Crowley MT, Marko IP, Masse NF, Andreev AD, Sweeney SJ, O'Reilly EP, Adams AR (2008) The importance of recombination via excited states in InAs/GaAs 1.3¼m quantum dot lasers, IEEE Proceedings of 21st International Semiconductor Laser Conference pp. 117-118 IEEE
The optical matrix element for excited-states is significantly weaker than the ground-state leading to thermally stable radiative recombination. This is not so for non-radiative Auger recombination, causing a sharp increase in threshold current with temperature.
Jarvis SD, Mukherjee J, Perren M, Sweeney SJ (2014) Development and characterisation of laser power converters for optical power transfer applications, IET Optoelectronics 8 (2) pp. 64-70
Interest in single-junction photovoltaic devices has been renewed in recent years due to their potential to produce very high optical to electrical conversion efficiencies under monochromatic illumination. A single-junction photovoltaic converter was developed for monochromatic radiation (a laser power converter (LPC)) to specifically convert monochromatic light at a wavelength of 1.55 ¼m (which is eye and skin safe up to a power density of 1 kW/m2) into electrical energy. Such devices find use in space-based laser power transfer, as well as fibre optic power delivery and the remote powering of subcutaneous equipment and other electrical devices. The LPC design is based on lattice-matched InGaAsP/InP, which includes elements for photon recycling and efficient carrier extraction. Here, the design process is reported based on computer simulated characteristics, and compare them to experimental data from both laboratory and field tests. The LPC demonstrates a conversion efficiency of 45% ± 1% under illumination at 1.55 ¼m and 1 kW/m2, and a conversion efficiency of 13.3% under AM1.5 solar illumination for potential dual-use applications. With further design optimisation, it has been predicted that the conversion efficiency will exceed 50% at 1.55 ¼m and 1 kW/m2. © The Institution of Engineering and Technology 2014.
Jin SR, Fehse R, Sweeney SJ, Knowles G, Adams AR, O'Reilly EP, Reichert H, Illek S, Egorov AY, Thijs PJA, Uchida T, Fujii T (2002) Modal refractive index of 1.3 mu m InGaAsP, AlGaInAs and GaInNAs semiconductor lasers under high hydrostatic pressure, ELECTRONICS LETTERS 38 (7) pp. 325-327 IEE-INST ELEC ENG
Sale TE, Knowles GC, Sweeney SJ, Onischenko A, Frost JEF, Pinches SM, Woodhead J (2000) -180 to +80 degrees C CW lasing in visible VCSELs, 2000 IEEE 17TH INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE, CONFERENCE DIGEST pp. 15-16 IEEE
Massé NF, Sweeney SJ, Marko IP, Andreev AD, Adams AR, Hatori N, Sugawara M (2006) Intrinsic limitations of p-doped and undoped 1.3 ¼m InAs/GaAs quantum dot lasers, Conference Digest - IEEE International Semiconductor Laser Conference pp. 143-144
Fehse R, O'Reilly EP, Sweeney SJ, Adams AR, McConville D, Riechert H, Geelhaar L (2005) Investigation of carrier recombination processes and transport properties in GaInAsN/GaAs quantum wells, AIP Conference Proceedings 772 pp. 985-986 American Institute of Physics
It is shown that the dramatic changes in threshold current density with changing active region growth temperature in 1.3¼m 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.
Chai GMT, Broderick CA, O'Reilly EP, Othaman Z, Jin SR, Petropoulos JP, Zhong Y, Dongmo PB, Zide JMO, Sweeney SJ, Hosea TJC (2015) Experimental and modelling study of InGaBiAs/InP alloys with up to 5.8% Bi, and with Delta(so) > E-g, SEMICONDUCTOR SCIENCE AND TECHNOLOGY 30 (9) ARTN 09401 IOP PUBLISHING LTD
Hossain N, Jin SR, Sweeney SJ, Yu S-Q, Johnson SR, Ding D, Zhang Y-H (2010) Improved Performance of GaAsSb/GaAs SQW Lasers, NOVEL IN-PLANE SEMICONDUCTOR LASERS IX 7616 SPIE-INT SOC OPTICAL ENGINEERING
Sweeney SJ, Lyons LJ, Lock D, Adams AR (2002) Direct measurement of facet temperature up to the melting point and COD in high power 980 nm semiconductor diode lasers, Conference Digest - IEEE International Semiconductor Laser Conference pp. 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.
Knowles G, Sweeney SJ, Sale TE, Adams AR (2001) Assessing the performance of visible (665 nm) vertical cavity surface emitting lasers using high pressure and low temperature techniques, PHYSICA STATUS SOLIDI B-BASIC RESEARCH 223 (2) pp. 581-585 WILEY-V C H VERLAG GMBH
Jin SR, Sweeney SJ, Tomic S, Adams AR, Riechert H (2003) Quantifying pressure-dependent recombination currents in GaInNAs lasers using spontaneous emission measurements, PHYSICA STATUS SOLIDI B-BASIC RESEARCH 235 (2) pp. 486-490 WILEY-V C H VERLAG GMBH
Masse NF, Homeyer E, Marko IP, Adams AR, Sweeney SJ, Dehaese O, Piron R, Grillot F, Loualiche S (2007) Temperature and pressure dependence of the recombination processes in 1.5 mu m InAs/InP (311)B quantum dot lasers, APPLIED PHYSICS LETTERS 91 (13) ARTN 131113 AMER INST PHYSICS
Hossain N, Sweeney SJ, Rogowsky S, Ostendorf R, Wagner J, Liebich S, Zimprich M, Volz K, Kunert B, Stolz W (2011) Reduced threshold current dilute nitride Ga(NAsP)/GaP quantum well lasers grown by MOVPE, ELECTRONICS LETTERS 47 (16) pp. 931-933 INST ENGINEERING TECHNOLOGY-IET
Masse NF, Sweeney SJ, Marko IP, Adams AR, Hatori N, Sugawara M (2006) Temperature dependence of the gain in p-doped and intrinsic 1.3 mu m InAs/GaAs quantum dot lasers, APPLIED PHYSICS LETTERS 89 (19) ARTN 191118 AMER INST PHYSICS
Higashi T, Sweeney SJ, Phillips AF, Adams AR, O'Reilly EP, Uchida T, Fujii T (1999) Experimental analysis of temperature dependence in 1.3-mu m AlGaInAs-InP strained MQW lasers, IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS 5 (3) pp. 413-419 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Marko I, Broderick CA, Jin S, Ludewig P, Stolz W, Volz K, Rorison JM, O?Reilly EP, Sweeney SJ (2016) Optical gain in GaAsBi/GaAs quantum well diode lasers, Scientific Reports 6 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.
Higashi T, Sweeney SJ, Phillips AF, Adams AR, O'Reilly EP, Uchida T, Fujii T (1999) Observation of reduced nonradiative current in 1.3-mu m AlGaInAs-InP strained MQW lasers, IEEE PHOTONICS TECHNOLOGY LETTERS 11 (4) pp. 409-411 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Adams AR, Silver M, OReilly EP, Gonul B, Phillips AF, Sweeney SJ, Thijs PJA (1996) Hydrostatic pressure dependence of the threshold current in 1.5 mu m strained quantum well lasers, PHYSICA STATUS SOLIDI B-BASIC RESEARCH 198 (1) pp. 381-388 AKADEMIE VERLAG GMBH
Chamings J, Ahmed S, Adams AR, Sweeney SJ, Odnoblyudov VA, Tu CW, Kunert B, Stolz W (2009) Band anti-crossing and carrier recombination in dilute nitride phosphide based lasers and light emitting diodes, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 246 (3) pp. 527-531 WILEY-V C H VERLAG GMBH
Chamings J, Adams AR, Sweeney SJ, Kunert B, Volz K, Stolz W (2008) Thermal properties of Silicon compatible GaNAsP SQW lasers, 2008 IEEE 21ST INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE pp. 61-62 IEEE
Higashi T, Sweeney SJ, Phillips AF, Adams AR, O'Reilly EP, Uchida T, Fujii T (1998) Observation of reduced non-radiative recombination current in 1.3-¼m AlGaInAs/InP multiple-quantum-well lasers, Conference Digest - IEEE International Semiconductor Laser Conference pp. 61-62
We investigated experimentally the temperature dependence of the threshold current in 1.3-¼m 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.
Hossain N, Jin SR, Sweeney SJ, Liebich S, Reinhard S, Volz K, Kunert B, Stolz W (2010) Physical properties of Ga(NAsP)/GaP QW lasers grown by MOVPE, 23rd Annual Meeting of the IEEE Photonics Society pp. 65-66 IEEE
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.
Tan SL, Zhang S, Soong WM, Goh YL, Tan LJJ, Ng JS, David JPR, Marko IP, Adams AR, Sweeney SJ, Allam J (2011) GaInNAsSb/GaAs Photodiodes for Long-Wavelength Applications, IEEE ELECTRON DEVICE LETTERS 32 (7) pp. 919-921 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Sweeney SJ, Jin SR, Fehse R, Adams AR, Higashi T, Riechert H, Thijs PJA (2002) A comparison of the thermal stability of InGaAsP, AlGaInAs and GaInNAs quantum-well lasers for 1.3 ¼m operation, Conference Digest - IEEE International Semiconductor Laser Conference pp. 43-44
The thermal stabilities of InGaAsP, AlGaInAs and GaInNAs quantum-well lasers for 1.3 ¼m 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.
Mohmad AR, Bastiman F, Ng JS, Sweeney SJ, David JPR (2011) Photoluminescence investigation of high quality GaAs1-xBix on GaAs, APPLIED PHYSICS LETTERS 98 (12) ARTN 122107 AMER INST PHYSICS
Hild K, Sale TE, Sweeney SJ, Hirotani M, Mizuno Y, Kato T (2004) Modulation speed resonant-cavity and leakage current in 650 nm light emitting diodes, IEE PROCEEDINGS-OPTOELECTRONICS 151 (2) pp. 94-97 IEE-INST ELEC ENG
Knowles G, Fehse R, Tomi? S, Sweeney SJ, Sale TE, Adams AR, O'Reilly EP, Steinle G, Riechert H (2002) The temperature and pressure dependence of 1.3 ¼m GaInNAs vertical-cavity surface emitting lasers (VCSELs), Conference Digest - IEEE International Semiconductor Laser Conference pp. 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.
Crutchley BG, Marko IP, Adams AR, Sweeney SJ (2013) Investigating the efficiency limitations of GaN-based emitters, Optics InfoBase Conference Papers
Lock D, Sweeney SJ, Adams AR, Deubner S, Klopf F, Reithmaier JP, Forchel A (2004) Carrier leakage suppression utilising short-period superlattices in 980 nm InGaAs/GaAs quantum well lasers, PHYSICA STATUS SOLIDI B-BASIC RESEARCH 241 (14) pp. 3405-3409 WILEY-V C H VERLAG GMBH
Murdin BN, Adams AR, Sweeney SJ (2006) Band structure and high-pressure measurements, Springer Series in Optical Sciences 118 pp. 93-127
Determination of the electronic energy vs momentum relationship in semiconductors is essential for the prediction of almost all of their properties. In materials useful for mid-infrared applications, the simplest parabolic band approximations are usually insufficient. However relatively straight-forward numerical techniques based on the k.p method can yield good predictions for the bandstructure. The theoretical bandstructures can be compared with experiment using magneto-optics and magneto-transport, but one of the most useful tools for controllably tuning the system is hydrostatic stress. The strain modifies the bandstructure in a rather s imple way, principally by a linear increase in the fundamental gap, and thus it can be used to separate out effects that depend on bandgap. A large literature has built up on the study of near-infrared optoelectronic devices under pressure. These have been used to establish the variations of the radiative and non-radiative Auger recombination processes with band structure. The results predict that III-V mid-IR lasers with direct band gaps less than the spin-orbit gap should have threshold current densities less than the near-IR lasers based on InP or GaAs. These predictions are found to be consistent with the threshold current density and its variation with pressure observed in InGaAsSb/AlGaAsSb operating at 2.37¼m at atmospheric pressure. Clearly high-pressure techniques provide exciting opportunities for the study of mid-infrared devices. © 2006 Springer-Verlag London Limited.
Hossain N, Jin SR, Sweeney SJ, Liebich S, Ludewig P, Zimprich M, Kunert B, Volz K, Stolz W (2010) Lasing properties of monolithically integrated Ga(NAsP)/(BGa)P QW lasers on a Silicon substrate grown by MOVPE, 22nd IEEE International Semiconductor Laser Conference pp. 109-110
Crowley MT, Marko IP, Masse NF, Andreev AD, Tomic S, Sweeney SJ, O'Reilly EP, Adams AR (2009) The Importance of Recombination via Excited States in InAs/GaAs 1.3 mu m Quantum-Dot Lasers, IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS 15 (3) pp. 799-807 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Masse NF, Marko IP, Adams AR, Sweeney SJ (2009) Temperature insensitive quantum dot lasers: are we really there yet?, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS 20 pp. 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.
Sweeney SJ, Hild K, Jin S (2013) The potential of GaAsBiN for multi-junction solar cells, Conference Record of the IEEE Photovoltaic Specialists Conference pp. 2474-2478
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. © 2013 IEEE.
Sweeney SJ, Phillips AF, Adams AR, O'Reilly EP, Silver M, Thijs PJA (1998) Transition from radiative to nonradiative recombination in 1.3-¼m and 1.5-¼m InGaAs(P) multiple quantum well semiconductor diode lasers, Conference on Lasers and Electro-Optics Europe - Technical Digest
Measurements of the threshold current, Ith as a function of temperature, T were performed on 1.3 ¼m and 1.5 ¼m 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.
Sweeney S (2009) Optoelectronic Devices, GB0911134.5
Sweeney SJ (2010) Bismide-alloys for higher efficiency infrared semiconductor lasers, 22nd IEEE International Semiconductor Laser Conference pp. 111-112 IEEE
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.
Fox NE, Sharma TK, Sweeney SJ, Hosea TJC (2009) Room temperature characterisation of InGaAlAs quantum well laser structures using electro-modulated reflectance and surface photovoltage spectroscopy, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 206 (5) pp. 796-802 WILEY-BLACKWELL
Knowles G, Tomic S, Jin S, Fehse R, Sweeney SJ, Sale TE, Adams AR (2003) Gain-cavity alignment profiling of 1.3 mu m emitting GaInNAs vertical cavity surface emitting lasers (VCSELs) using high pressure techniques, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 235 (2) pp. 480-485 WILEY-V C H VERLAG GMBH
Adams AR, Fehse R, Tomic S, O'Reilly EP, Andreev A, Knowles G, Sale TE, Sweeney SJ, Steinle G, Ramakrishnan A, Riechert H (2002) Characterisation of 1.3pm wavelength GaInNAs/GaAs edge-emitting and vertical-cavity surface-emitting lasers using low-temperature and high-pressure, APOC 2002: ASIA-PACIFIC OPTICAL AND WIRELESS COMMUNICATIONS; MATERIALS AND DEVICES FOR OPTICAL AND WIRELESS COMMUNICATIONS 4905 pp. 183-197 SPIE-INT SOC OPTICAL ENGINEERING
Ikyo BA, Marko IP, Adams AR, Sweeney SJ, Canedy CL, Vurgaftman I, Kim CS, Kim M, Bewley WW, Meyer JR (2010) Temperature sensitivity of mid-infrared type II "W" interband cascade lasers (ICL) emitting at 4.1¼m at room temperature, 22nd IEEE International Semi-conductor Laser Conference pp. 41-42 IEEE
The thermal properties of 5-stage ?W? Interband-Cascade Lasers emitting at 4.1¼m at RT are investigated. It is shown that inter-valence band absorption coupled with non-radiative recombination govern their maximum operating temperature.
Marko IP, Sweeney SJ (2015) Optical and electronic processes in semiconductor materials for device applications, Springer Series in Materials Science 203 pp. 253-297
© Springer Science+Business Media Singapore 2015.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.
Sweeney SJ, Adams AR, O'Reilly EP, Silver M, Thijs PJA (2000) Effect of auger generated hot-holes on 1.5-¼m InGaAs(P)-based quantum well semiconductor lasers, Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digest pp. 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 1.5-¼m semiconductor lasers. Results of the study clearly highlight the design implications of both quantum well placement and total waveguide thickness on laser performance.
Green BC, Yu S-Q, Sweeney SJ, Ding D, Zhang Y-H (2008) Novel heterostructure design for increased spectral width of superluminescentdiodes and dual-wavelength laser diodes, Device Research Conference - Conference Digest pp. 309-310
Superluminescent diodes (SLDs) based on amplified spontaneous emission are used in numerous applications such as optical coherence tomography where the short coherence length due to the broad spectral width enables high resolution images. Multiple approaches have been made to broaden the spectrum of SLDs to reduce the coherence length further. These include multi-quantum well (MQW) designs with different effective band gaps formed either by different well widths or different well compositions. These MQWs forming the active region of the device are conventionally located within the intrinsic region of a p-i-n junction diode and have common quasi-Fermi levels determined by the current injection and carrier lifetime. The overall spectral width of these devices however narrows at high injection levels when the injection is increased to reach the desired output power. This spectral narrowing is due to the disproportionate increase in gain for different wavelengths as the injection is increased.
Tan LJJ, Soong WS, Tan SL, Goh YL, Steer MJ, Ng JS, David JPR, Marko IP, Chamings J, Allam J, Sweeney SJ, Adams AR (2009) Dark current mechanisms in InxGa1-xAs 1-yNy, IEEE Proceedings of LEOS Annual Meeting Conference pp. 233-234 IEEE
In order to extend the photo response of GaAs to optical telecommunication wavelengths, In and N can be incorporated into GaAs to yield a perfect lattice match of InxGa1-xAs1-yNy with GaAs with a bandgap that strongly decreases with increasing N composition. The potential usage of such a material as photodetectors and photovoltaic applications has been reported.In this work, we investigate the dark current mechanisms in the InxGa1-xAs1-yNy material.
Marko IP, Masse NF, Sweeney SJ, Adams AR, Hatori N, Sugawara M (2007) Recombination, transport and loss mechanisms in p-doped InAs/GaAs quantum dots, Physics of Semiconductors, Pts A and B 893 pp. 837-838 AMER INST PHYSICS
Ikyo BA, Marko IP, Hild K, Adams AR, Arafin S, Amann MC, Sweeney SJ (2013) The effect of hole leakage and auger recombination on the temperature sensitivity of GaInAsSb/GaSb mid-infrared lasers, Optics InfoBase Conference Papers
Simmons RA, Jin SR, Sweeney SJ, Clowes SK (2015) Enhancement of Rashba interaction in GaAs/AlGaAs quantum wells due to the incorporation of bismuth, APPLIED PHYSICS LETTERS 107 (14) ARTN 142401 AMER INST PHYSICS
Marko IP, Adams AR, Sweeney SJ, Jin SR, Murdin BN, Schwertberger R, Somers A, Reithmaier JP, Forchel A (2004) Experimental investigations into the thermal properties of 1.5-1.8-mu m InAs/InP quantum dash lasers, 2004 IEEE 19TH INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE, CONFERENCE DIGEST pp. 61-62 IEEE
Hild K, Sweeney SJ, Wright S, Lock DA, Jin SR, Marko IP, Johnson SR, Chaparro SA, Yu S-Q, Zhang Y-H (2006) Carrier recombination in 1.3 mu m GaAsSb/GaAs quantum well lasers, APPLIED PHYSICS LETTERS 89 (17) ARTN 173509 AMER INST PHYSICS
Jin S, John Sweeney S (2013) InGaAsBi alloys on InP for efficient near- and mid-infrared light emitting devices, Journal of Applied Physics 114 (21)
We present the band parameters such as band gap, spin-orbit splitting energy, band offsets and strain of InGaAsBi on InP based on recent experimental data. It is shown that InGaAsBi is promising for near- and mid-infrared photonic devices operating from 0.3-0.8 eV (1.5-4 ¼m) on conventional InP substrates. We also show how bismuth may be used to form alloys whereby the spin-orbit splitting energy (SO) is large and controllable and can, for example, be made larger than the band gap (Eg) thereby providing a means of suppressing non-radiative hot-hole producing Auger recombination and inter-valence band absorption both involving the spin-orbit band. This is expected to improve the high-temperature performance and thermal stability of light emitting devices. © 2013 AIP Publishing LLC.
Sweeney SJ, Phillips AF, Adams AR, O'Reilly EP, Thijs PJA (1998) Determination of the influence of Auger recombination on the threshold current of 1.3 ¼m and 1.5 ¼m InGaAs(P) strained-layer lasers and its variation with temperature, Conference Digest - IEEE International Semiconductor Laser Conference pp. 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 ¼m and at 1.3 ¼m respectively.
McConville DG, Sweeney SJ, Adams AR, Tomic S, Riechert H (2007) Temperature and pressure dependence of the recombination mechanisms in 1.3 pm and 1.5 pm GaInNAs lasers, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 244 (1) pp. 208-212 WILEY-V C H VERLAG GMBH
Marko IP, Masse NF, Sweeney SJ, Andreev AD, Adams AR, Hatori N, Sugawara M (2005) Carrier transport and recombination in p-doped and intrinsic 1.3 mu m InAs/GaAs quantum-dot lasers, APPLIED PHYSICS LETTERS 87 (21) ARTN 211114 AMER INST PHYSICS
Marko IP, Aldukhayel AM, Adams AR, Sweeney SJ, Teissier R, Baranov AN, Tomi? S (2010) Physical properties of short wavelength 2.6¼m InAs/AlSb-based quantum cascade lasers, Conference Digest - IEEE International Semiconductor Laser Conference pp. 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.
Sweeney SJ, Lock DA, Adams AR (2005) Carrier recombination in InGaAs(P) quantum well laser structures: Band gap and temperature dependence, Physics of Semiconductors, Pts A and B 772 pp. 1545-1546 AMER INST PHYSICS
Lealman I, Dosanjh S, Rivers L, O'Brien S, Cannard P, Sweeney SJ, Marko IP, Rushworth S (2008) Reliable 1550nm SI BH lasers fabricated using an improved Ru precursor, 20th International Conference on Indium Phosphide and Related Materials
We have fabricated and assessed 1550 nm SIBH FP lasers using a novel Ruthenium precursor for MOVPE. Low temperature analysis revealed no unexpected defects and performance is similar to standard p-n-p-n current blocking devices. Accelerated aging at 85degC indicates no significant degradation after 5,700 hours on test.
Sale TE, Sweeney SJ, Knowles G, Adams AR (2001) Gain-cavity alignment in efficient visible (660 nm) VCSELs studied using high pressure techniques, PHYSICA STATUS SOLIDI B-BASIC RESEARCH 223 (2) pp. 587-591 WILEY-V C H VERLAG GMBH
Marko P, Adams AR, Sweeney SJ, Whitbread ND, Ward AJ, Asplin B, Robbins J (2007) The influence of carrier density non-pinning on the output power of 1.55 ¼m lasers at high temperature, Optics InfoBase Conference Papers
Coote J, Reddy S, Sweeney SJ (2007) Optimisation of distributed feedback laser biosensors, IET OPTOELECTRONICS 1 (6) pp. 266-271 INST ENGINEERING TECHNOLOGY-IET
Marko IP, Ikyo AB, Adams AR, Sweeney SJ, Bachmann A, Kashani-Shirazi K, Amann MC (2009) Band-structure and gain-cavity tuning of 2.4-¼m GaSb buried tunnel junction VCSELs, Optics InfoBase Conference Papers
Phillips AF, Sweeney SJ, Adams AR, Thijs PJA (1999) The temperature dependence of 1.3-and 1.5-mu m compressively strained InGaAs(P) MQW semiconductor lasers, IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS 5 (3) pp. 401-412 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Broderick CA, Usman M, O'Reilly EP, Broderick CA, O'Reilly EP, Sweeney SJ (2012) Band engineering in dilute nitride and bismide semiconductor lasers, Semiconductor Science and Technology 27 (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.
Sweeney SJ, Krause S (2009) Editorial: Selected papers from the second international conference on optical, optoelectronic and photonic materials and applications, 2007, Journal of Materials Science: Materials in Electronics 20 (SUPPL. 1) pp. S1-S2 Springer
Sayid SA, Marko IP, Cannard PJ, Chen X, Rivers LJ, Lealman IF, Sweeney SJ (2010) Thermal Characteristics of 1.55-mu m InGaAlAs Quantum Well Buried Heterostructure Lasers, IEEE JOURNAL OF QUANTUM ELECTRONICS 46 (5) pp. 700-705 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
O'Brien K, Sweeney SJ, Adams AR, Jin SR, Ahmad CN, Murdin BN, Salhi A, Rouillard Y, Joullie A (2007) Carrier recombination mechanisms in mid-infrared GaInAsSb quantum well lasers, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 244 (1) pp. 203-207 WILEY-V C H VERLAG GMBH
Sayid SA, Marko IP, Cannard PJ, Chen X, Rivers LJ, Lealman IF, Sweeney SJ (2010) Thermal performance of 1.55¼m InGaAlAs quantum well buried heterostructure lasers, IEEE Proceedings of 22nd International Conference on Indium Phosphide and Related Materials pp. 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, ·i, is ~80% at 20°C remaining stable up to 80°C. In contrast, the internal optical loss, ±i, 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.
Ongrai O, Pearce JV, Machin G, Sweeney SJ (2011) A miniature high-temperature fixed point for self-validation of type C thermocouples, MEASUREMENT SCIENCE & TECHNOLOGY 22 (10) ARTN 105103
Marko IP, Adams AR, Sweeney SJ, Masse NF, Krebs R, Reithmaier JP, Forchel A, Mowbray DJ, Skolnick MS, Liu HY, Groom KM, Hatori N, Sugawara M (2007) Band gap dependence of the recombination processes in InAs/GaAs quantum dots studied using hydrostatic pressure, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 244 (1) pp. 82-86 WILEY-V C H VERLAG GMBH
Batool Z, Hild K, Hosea TJC, Lu X, Tiedje T, Sweeney SJ (2012) The electronic band structure of GaBiAs/GaAs layers: Influence of strain and band anti-crossing, JOURNAL OF APPLIED PHYSICS 111 (11) ARTN 113108 AMER INST PHYSICS
Mohmad AR, Bastiman F, Ng JS, Sweeney SJ, David JPR (2012) Room temperature photoluminescence intensity enhancement in GaAs 1-xBi x alloys, Physica Status Solidi (C) Current Topics in Solid State Physics 9 (2) pp. 259-261
Sweeney SJ, Higashi T, Adams AR, Uchida T, Fujii T (2000) A comparison of AlGaInAs and InGaAsP-based 1.3 mu m semiconductor lasers using high pressure, HIGH PRESSURE RESEARCH 18 (1-6) pp. 49-55 GORDON BREACH SCI PUBL LTD
Knowles G, Sweeney SJ, Sale T (2001) Influence of leakage and gain-cavity alignment on the performance of Al(GaInP) visible vertical-cavity surface emitting lasers, IEE PROCEEDINGS-OPTOELECTRONICS 148 (1) pp. 55-59 IEE-INST ELEC ENG
Sweeney SJ, Knowles G, Sale TE (2001) Evaluating the continuous-wave performance of AlGaInP-based red (667 nm) vertical-cavity surface-emitting lasers using low-temperature and high-pressure techniques, APPLIED PHYSICS LETTERS 78 (7) pp. 865-867 AMER INST PHYSICS
O'Brien K, Adams AR, Sweeney SJ, Jin SR, Ahmad CN, Murdin BN, Canedy CL, Vurgaftman I, Meyer JR (2007) High pressure studies of mid-infrared type-II "W" diode lasers at cryogenic temperatures, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 244 (1) pp. 224-228 WILEY-V C H VERLAG GMBH
Ikyo AB, Marko IP, Hild K, Adams AR, Arafin S, Amann M-C, Sweeney SJ Temperature stable mid-infrared GaInAsSb/GaSb Vertical Cavity Surface Emitting Lasers (VCSELs), NATURE PUBLISHING GROUP
Sweeney SJ, Higashi T, Adams AR, Uchida T, Fujii T (1998) Improved temperature dependence of 1.3 mu m AlGalnAs-based MQW semiconductor diode lasers revealed by hydrostatic pressure, ELECTRONICS LETTERS 34 (22) pp. 2130-2132 IEE-INST ELEC ENG
Sweeney S, Fehse R, Adams AR, Riechert H (2003) Intrinsic temperature sensitivities of 1.3 mu m GaInNAs/GaAs, InGaAsP/InP and AlGaInAs/InP-based semiconductor lasers, 2003 IEEE LEOS ANNUAL MEETING CONFERENCE PROCEEDINGS, VOLS 1 AND 2 pp. 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.

Ng JS, Soong WM, Steer MJ, Hopkinson M, David JPR, Chamings J, Sweeney SJ, Adams AR (2007) Long wavelength bulk GaInNAs p-i-n photodiodes lattice matched to GaAs, JOURNAL OF APPLIED PHYSICS 101 (6) ARTN 064506 AMER INST PHYSICS
Liebich S, Zimprich M, Ludewig P, Beyer A, Volz K, Stolz W, Kunert B, Hossain N, Jin SR, Sweeney SJ (2010) MOVPE growth and characterization of Ga(NAsP) laser structures monolithically integrated on Si (001) substrates, 22nd IEEE International Semiconductor Laser Conference pp. 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.
Hossain N, Hosea J, Liebich S, Zimprich M, Volz K, Kunert B, Stolz W, Sweeney S (2013) Band Structure Properties of (BGa)P Semiconductors for Lattice Matched Integration on (001) Silicon, PHYSICS OF SEMICONDUCTORS 1566 pp. 47-48 AMER INST PHYSICS
Ikyo AB, Marko IP, Adams AR, Sweeney SJ, Bachmann A, Kashani-Shirazi K, Amann M-C (2009) Gain peak-cavity mode alignment optimisation in buried tunnel junction mid-infrared GaSb vertical cavity surface emitting lasers using hydrostatic pressure, IET OPTOELECTRONICS 3 (6) pp. 305-309 INST ENGINEERING TECHNOLOGY-IET
Tan SL, Tan LJJ, Goh YL, Zhang S, Ng JS, David JPR, Marko IP, Allam J, Sweeney SJ, Adams AR (2010) Reduction of dark current and unintentional background doping in InGaAsN photodetectors by ex situ annealing, Proceedings of SPIE - Posters Session 7726 SPIE
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 ¼A/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 ¼m. Evidence of lower unintentional background concentration after annealing at a sufficiently high temperature, is also presented.
Chamings J, Adams AR, Sweeney SJ, Kunert B, Volz K, Stolz W (2008) Temperature dependence and physical properties of Ga(NAsP)/GaP semiconductor lasers, APPLIED PHYSICS LETTERS 93 (10) ARTN 101108 AMER INST PHYSICS
Bushell Z, Florescu M, Sweeney S (2017) High-Q photonic crystal cavities in all-semiconductor photonic crystal heterostructures, Physical Review B 95 (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.
Marko I, Sweeney S (2017) Progress towards III-V-Bismide Alloys for Near- and Mid-Infrared Laser Diodes, IEEE Journal of Selected Topics in Quantum Electronics 23 (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 (SO) is greater than the bandgap (Eg) in the active region for devices operating around the telecom wavelength of 1.55 ¼m, thereby suppressing the dominant efficiency-limiting loss processes in such lasers, namely Auger recombination and inter-valence band absorption (IVBA). The SO > Eg band structure is present in GaAsBi alloys containing > 10% Bi, at which composition the alloy band gap is close to 1.55 ¼m 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.
Sweeney S, Lyons L, Adams AR, Lock D (2003) Direct measurement of facet temperature up to melting point and COD in high-power 980-nm semiconductor diode lasers, IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS 9 (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.

Jin S, Sweeney S, Tomic S, Adams AR, Riechert H (2003) High-pressure studies of recombination mechanisms in 1.3-mu m GaInNAs quantum-well lasers, IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS 9 (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.

Tan S, Hunter C, Zhang S, Tan L, Goh Y, Ng J, David J, Marko I, Sweeney S, Adams AR, Allam J (2012) Improved optoelectronic properties of rapid thermally annealed dilute nitride GaInNAs photodetectors, Journal of Electronic Materials 41 (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.
Fehse R, Sweeney S, Adams AR, McConville D, Riechert H, Geelhaar L (2004) Influence of growth temperature on defect density in 1.3 mu m GaInNAs-based lasers, 2004 IEEE 19TH INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE, CONFERENCE DIGEST pp. 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.

Maspero Ross, Sweeney Stephen, Florescu Marian (2016) Unfolding the band structure of GaAsBi, Journal of Physics: Condensed Matter 29 (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%.
Crutchley B, Marko I, Adams AR, Sweeney S (2013) Investigating the efficiency limitations of GaN-based emitters, 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.
Knowles G, Fehse R, Tomic S, Sweeney S, Sale T, Adams AR, O'Reilly P, Steinle G, Riechert H (2003) Investigation of 1.3-mu m GaInNAs vertical-cavity surface-emitting lasers (VCSELs) using temperature, high-pressure, and modelling techniques, IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS 9 (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.

Broderick CA, Jin S, Marko Igor, Hild Konstanze, Ludewig P, Bushell Zoe, Stolz W, Rorison JM, O?Reilly EP, Volz K, Sweeney Stephen (2017) GaAs1?xBix/GaNyAs1?y type-II quantum wells: novel strain-balanced heterostructures for GaAs-based near- and mid-infrared photonics, Scientific Reports 7 46371 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 ¼m 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 ¼m 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.
Bueckers C, Blume G, Thraenhardt A, Schlichenmaier C, Klar P, Weiser G, Koch S, Hader J, Moloney J, Hosea TJC, Sweeney S, Wang J, Johnson S, Zhang Y (2007) Microscopic electroabsorption line shape analysis for Ga(AsSb)/GaAs heterostructures, JOURNAL OF APPLIED PHYSICS 101 (3) ARTN 0 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.

Hild K, Sweeney S, Lock D, Wright S, Wang J, Johnson S, Zhang Y (2005) On the thermal stability of 1.3 mu m GaAsSb/GaAs-based lasers, 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.
Marko Igor, Read GW, Hossain N, Sweeney Stephen (2015) Physical Properties and Characteristics of III-V Lasers on Silicon, IEEE Journal of Selected Topics in Quantum Electronics 21 (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.
Marko Igor, Adams Alfred, Sweeney Stephen, Sellers IR, Mowbray DJ, Skolnick MS, Liu HY, Groom KM (2004) Recombination and loss mechanisms in low-threshold InAs/GaAs 1.3 mu m quantum dot lasers, 2004 IEEE 19TH INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE, CONFERENCE DIGEST pp. 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.
Marko Igor, Adams Alfred, Sweeney Stephen, Mowbray DJ, Skolnick MS, Liu HYY, Groom KM (2005) Recombination and loss mechanisms in low-threshold InAs-GaAs 1.3-mu m quantum-dot lasers, IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS 11 (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.

Adams Alfred, Marko Igor, Mukherjee J, Sweeney Stephen, Gocalinska A, Pelucchi E, Corbett B (2014) Semiconductor quantum well lasers with a temperature insensitive threshold current, Conference Digest - IEEE International Semiconductor Laser Conference pp. 82-83
Adams Alfred, Marko Igor, Mukherjee J, Stolojan Vlad, Sweeney Stephen, Gocalinska A, Pelucchi E, Thomas K, Corbett B (2015) Semiconductor Quantum Well Lasers With a Temperature-Insensitive Threshold Current, IEEE Journal of Selected Topics in Quantum Electronics 21 (6) 150080 pp. ?-? 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 ¼m 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.
Sweeney S, McConville D, Jin S, Ahmad C, Masse N, Bouyssou R, Adams AR, Hanke C (2004) Temperature and wavelength dependence of recombination processes in 1.5 mu m InGaAlAs/InP-based lasers, 2004 International Conference on Indium Phosphide and Related Materials, Conference Proceedings pp. 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.

Tomic S, O'Reilly E, Fehse R, Sweeney S, Adams AR, Andreev AD, Choulis S, Hosea TJC, Riechert H (2003) Theoretical and experimental analysis of 1.3-mu m InGaAsN/GaAs lasers, IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS 9 (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.

Lock D, Sweeney S, Adams AR (2003) Wavelength dependence of catastrophic optical damage threshold in 980nm semiconductor diode lasers, 2003 IEEE LEOS ANNUAL MEETING CONFERENCE PROCEEDINGS, VOLS 1 AND 2 pp. 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.

This thesis investigates a range of novel photonic devices and their constituent semiconductor materials with emission in the infrared (IR) region of the spectrum. These have a variety of potential applications, including in telecoms, sensing and defence systems. Studies focus on aspects of the electronic and photonic band structures, and how these impact upon device performance.

Type-II interband cascade lasers and LEDs emitting in the mid-IR region of 3 ? 4 ¼m are characterised using temperature and hydrostatic pressure dependent techniques. The key finding is that the threshold current density exhibits a minimum for emission around 0.35 eV (~3.5 ¼m), in both the pressure dependent results and data for many devices with different design wavelengths. The increase in threshold current density towards lower energies can be explained by an increase in CHCC Auger recombination. The increase in threshold current towards higher energies cannot be well explained by an Auger process, and it is concluded that this may be evidence of defect-related recombination.

Dilute bismide alloys are an interesting new material system for IR applications. The electronic and optical properties of several dilute bismide alloys are determined by spectroscopic ellipsometry. Key findings include the first experimental measurements of the spin-orbit splitting in GaNAsBi, which show that it is approximately independent of N content, and the first evidence for a decrease in the direct band gap of GaP with the addition of bismuth, reducing by 130 ± 20 meV/%Bi. The refractive index was determined for all the materials and in the transparency region the real part of the refractive index was found to decrease approximately linearly with increasing band gap.
In addition to modifying the electronic properties, photonic effects can be used to develop new IR devices. Finite difference time domain simulations of photonic crystal cavity structures within thick multi-layer slabs were carried out. These showed that it is possible to achieve high Q-factors, > 10^4, in slabs with refractive indices corresponding to typical semiconductor heterostructures. This opens up possibilities for designing photonic crystal lasers that do not require the thin suspended membranes typically found in the literature, with applications in integrated photonic circuits and on-chip sensors.

This work describes the design, development and characterisation of high efficiency photovoltaics (laser power converters) for the conversion of monochromatic light from a laser source into electrical energy. The technology provides a means of transmitting power wirelessly through free-space, for applications in the remote powering of electrical devices and systems. It also provides a means of efficiently transmitting power though fibre-optic cables, allowing electrical power to be delivered free from electromagnetic interference.

The design of the laser power converter is considered for efficient conversion of monochromatic light at a target wavelength of 1550nm. This wavelength was chosen based on its ability to transmit through the atmosphere and silica-based fibre-optics with minimal losses. It also allows for the maximum exposure limit of 1kWm^-2 to be transmitted in free-space, which is eye- and skin-safe. Various semiconductor materials were explored for this design in terms of their maturity, band-gap tunability and lattice matching to common substrates.

The laser power converter was then developed based on the material system InGaAsP/InP with a band-gap tuned to match the incident target wavelength. These cells were then characterised using a tunable laser source and the best cell achieved a conversion efficiency (at 20 degrees) of 38.9% at an irradiance of 0.73kWm^-2 at the target wavelength. However, earlier field tests conducted by Dr. Jayanta Mukherjee demonstrated an efficiency of 45% at 1kWm^-2, which is much higher than conventional single-junction solar cells and currently holds the record for monochromatic PVs operating at 1550nm.

The various carrier recombination mechanisms that limit the efficiency are then investigated by measuring the cell performance down to temperatures of 100K. In this measurement the efficiency at 39Wm^-2 is shown to increase from 28.6% to 72% over the temperature range 300-100K and approaches the theoretical detailed-balance limit. An advanced temperature-dependent diode and resistance model is then formulated to predict the dominant carrier loss mechanisms at room temperature. It was found that (to a first approximation) defect-related carrier recombination dominates over the temperature range with a lifetime of 5us at room temperature. The model also determined a carrier mobility at room temperature of 12.4 cm^2V^-1s^-1 in the emitter layer, which results in a high sheet resistance and limits carrier tran

Eales Timothy, Marko Igor, Ikyo BA, Adams Alfred, Arafin S, Sprengel S, Amann M-C, Sweeney Stephen (2017) Wavelength dependence of efficiency limiting mechanisms in Type-I Mid-infrared GaInAsSb/GaSb lasers, IEEE Journal of Selected Topics in Quantum Electronics 23 (6) IEEE
The efficiency limiting mechanisms in type-I GaInAsSb-based quantum well (QW) lasers, emitting at 2.3 ¼m, 2.6 ¼m and 2.9 ¼m, 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 ¼m. 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 ¼m). At shorter wavelengths (
Jin S. R., Sweeney S. J., Ahmad C. N., Adams A. R., Murdin B. N. (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, Applied Physics Letters 357 (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

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.

O'Brien K., Sweeney S. J., Adams A. R., Murdin B. N, Salhi A., Rouillard Y., Joullié A. (2006) Recombination processes in midinfrared InGaAsSb diode lasers emitting at 2.37 µm, Applied Physics Letters 051104 (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.

Jin S. R., Ahmad C. N., Sweeney S. J., Adams A. R., Murdin B. N., Page H., Marcadet X., Sirtori C., Tomi? S. (2006) Spectroscopy of GaAs/AlGaAs quantum-cascade lasers using hydrostatic pressure, Applied Physics Letters 221105 (2006)
Jin S R, Ahmad C N, Sweeney S J, Adams A R, Murdin B N, Page H, Marcadet X, Sirtori C, Tomic S (2006) Spectroscopy of GaAs/AlGaAs Quantum-Cascade Lasers Using Hydrostatic Pressure, Applied Physics Letters 89 (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.

O'Brien K, Sweeney S J, Adams A R, Murdin B N, Salhi A, Rouillard Y, Joullie A (2006) Recombination Processes in Midinfrared InGaAsSb Diode Lasers Emitting at 2.37 mu m, Applied Physics Letters 89 (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.

The advances in semiconductor technology coupled with the potential of lab-on-chip spectroscopy, long wavelength telecommunications and small-scale optical interconnects has invigorated academic and commercial interest in mid-infrared optoelectronics. However, significant challenges remain. This thesis explores two approaches for mid-infrared optoelectronic lasers.
Type-I GaSb quantum well lasers exhibit some of the highest performance metrics of any semiconductor laser system in the 2 ¼m ? 3 ¼m wavelength range. However, the threshold current density increases substantially with increasing wavelength and temperature, impacting component reliability and the overall efficiency of a laser-based optoelectronic system.
Through a combination of temperature and hydrostatic pressure techniques, Auger recombination is identified as the dominant cause for the performance degradation of type-I mid-infrared laser with increasing wavelength and temperature. Using hydrostatic pressure measurements, the wavelength dependence of the Auger coefficient over the 2 ¼m - 3 ¼m range is constructed, revealing two important regimes. At wavelengths 2 ¼m, the CHSH process is effectively suppressed due to the energetic separation between the lasing energy and the spin-orbit split-off band. In this regime another Auger process, such as CHCC or CHLH recombination begins to dominate, increasing exponentially with wavelength. The temperature dependence of the radiative and non-radiative threshold current density indicates that this Auger process has an activated character and is sensitive to the intrinsic properties of the quantum well band structure.
To leverage the advanced manufacturing capabilities and high yields of the Si-microelectronics industry, there is intense research activity to realise CMOS compatible optoelectronics. One emerging strategy is to augment the optical properties of group-IV materials through band structure engineering, such as incorporating Sn into the Ge lattice.
Hydrostatic pressure measurements of the GeSn absorption edge exhibit an intermediate pressure coefficient between that of the  and L conduction band critical points. This is indicative of strong band mixing effects in the GeSn alloy. In the presence of band mixing the conventional distinction between the indirect and direct band gap breaks down. Instead it is more appropriate to discuss the nature of the band gap in terms of the fractional -character of the conduction band states at the band edge. The pressure coefficient of the absorption edge for samples with Sn content between 6% ? 10% reveal a continuous evolution in the -character with increasing Sn-concentration. High -character is observed even at low Sn concentrations of 6%, when the GeSn alloy is expected to exhibit a fundamentally indirect band gap. These band mixing effects have important implications for designing efficient photonic and electronic devices utilizing GeSn and related material systems.
Bushell Zoe L., Broderick Christopher A., Nattermann Lukas, Joseph Rita, Keddie Joseph L., Rorison Judy M., Volz Kerstin, Sweeney Stephen J. (2019) Giant bowing of the band gap and spin-orbit splitting energy in GaP1?ÇBiÇ dilute bismide alloys, Scientific Reports 9 (1) 6835 Nature Research
Using spectroscopic ellipsometry measurements on GaP1?ÇBiÇ/GaP epitaxial layers up to Ç = 3.7% we observe a giant bowing of the direct band gap (Eg) and valence band spin-orbit splitting energy (SO). EgSO) 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 SO in going from GaP to GaP0.99Bi0.01. The evolution of Eg and SO with Ç 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 Eg and SO with Ç. In contrast to the well-studied GaAs1?ÇBiÇ alloy, in GaP1?ÇBiÇ 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 Eg and SO and in particular for the giant bowing observed for Ç r 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?ÇBiÇ alloy band structure.
Eales Timothy D., Marko Igor P., Schulz Stefan, O?Halloran Edmond, Ghetmiri Seyed, Du Wei, Zhou Yiyin, Yu Shui-Qing, Margetis Joe, Tolle John, O?Reilly Eoin P., Sweeney Stephen J. (2019) Ge1-xSnx alloys: Consequences of band mixing effects for the evolution of the band gap -character with Sn concentration, 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) - character of the GeSn band gap changes continuously with alloy composition and has significant -character even at low (6%) Sn concentrations. The evolution of the -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.
Sharpe M. K., Marko I. P., Duffy D. A., England J., Schneider E., Kesaria M., Fedorov V., Clarke E., Tan C. H., Sweeney S. J. (2019) A comparative study of epitaxial InGaAsBi/InP structures using Rutherford backscattering spectrometry, X-ray diffraction and photoluminescence techniques, JOURNAL OF APPLIED PHYSICS 126 (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.
This thesis investigates novel range semiconductor materials and structures for use in optoelectronic devices operating from UV to mid-IR. These devices have an abundant variety of applications, including optical communications and imaging. The studies primarily focus on the electronic band structure of the materials and how this impacts device performance. Dilute bismide III-V alloys are a material of great interest for IR applications, especially with the band structure engineering that can be carried out to fulfil the condition where the spin-orbit splitting energy, ?
Waché Rémi, Fielder Tim, Dickinson Will E.C., Hall Joe L., Adlington Peter, Sweeney Stephen J., Clowes Steven K. (2020) Selective light transmission as a leading innovation for solar swimming pool covers, Solar Energy 207 pp. 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.