Alf Adams

Professor Alfred Adams


Professor Emeritus
FRS, BSc, PhD, DSc (Leicester) FInstP, CPhys, LFIEEE, HFIET, CEng, DUniv
+44 (0)1483 689310
21 ATI 02

Academic and research departments

Department of Physics.

Biography

Research

Research interests

My publications

Publications

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

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

Stephen Sweeney, LJ Lyons, Alfred Adams, DA Lock (2003)Direct measurement of facet temperature up to melting point and COD in high-power 980-nm semiconductor diode lasers, In: IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS9(5)pp. 1325-1332 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

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

S Ngarize, A Adams, NK Howell (2004)Studies on egg albumen and whey protein interactions by FT-Raman spectroscopy and rheology, In: FOOD HYDROCOLLOIDS18(1)pp. 49-59 ELSEVIER SCI LTD
M Bonte, O von dem Knesebeck, J Siegerist, L Marceau, C Link, S Arber, A Adams, JB McKinlay (2008)Women and men with coronary heart disease in three countries; Are they treated differently?, In: Women’s Health Issues18(3)pp. 191-198 Elsevier

Background Nonmedical determinants of medical decision making were investigated in an international research project in the United States, the United Kingdom, and Germany. The key question in this paper is whether and to what extent doctors' diagnostic and therapeutic decisions in coronary heart disease (CHD) are influenced by patient gender. Methods A factorial experiment with a videotaped patient consultation was conducted. Professional actors played the role of patients with symptoms of CHD. Several alternative versions were taped featuring the same script with patient-actors of different gender, age, race, and socioeconomic status. The videotapes were presented to a randomly selected sample of 128 primary care physicians in each country. Using an interview with standardized and open-ended questions, physicians were asked how they would diagnose and treat such a patient after they had seen the video. Results Results show gender differences in the diagnostic strategies of the doctors. Women were asked different questions, CHD was mentioned more often as a possible diagnosis for men than for women, and physicians were less certain about their diagnosis with female patients. Gender differences in management decisions (therapy and lifestyle advice) are less pronounced and less consistent than in diagnostic decisions. Magnitude of gender effect on doctors' decisions varies between countries with smaller influences in the United States. Conclusion Although patients with identical symptoms were presented, primary care doctors' behavior differed by patients' gender in all 3 countries under study. These gender differences suggest that women may be less likely to receive an accurate diagnosis and appropriate treatment than men.

NF Massé, SJ Sweeney, IP Marko, AD Andreev, AR Adams, N Hatori, M Sugawara (2006)Intrinsic limitations of p-doped and undoped 1.3 μm InAs/GaAs quantum dot lasers, In: 20th IEEE International Semi-conductor Laser Conference - Conference Digestpp. 143-144

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

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

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

S A Choulis, A Andreev, M Merrick, A R Adams, B N Murdin, A Krier, V V Sherstnev (2003)High-Pressure Measurements of Mid-Infrared Electroluminescence from InAs Light-Emitting Diodes at 3.3μm, In: Applied Physics Letters82(8)pp. 1149-1151

The spontaneous electroluminescence emission of InAs light-emitting diodes (LEDs) operating at 3.3 μm was studied as a function of applied hydrostatic pressure. An enhancement of a factor of almost four in radiative efficiency at room temperature was observed in the range 0 to 10 kbar. Analysis of the dependence of electroluminescence emission intensity on hydrostatic pressure at constant current reveals that nonradiative Auger recombination dominates the quantum efficiency of these LEDs

A Adams, CD Buckingham, A Lindenmeyer, JB McKinlay, C Link, L Marceau, S Arber (2008)The influence of patient and doctor gender on diagnosing Coronary Heart Disease, In: Sociology of Health and Illness30(1)pp. 1-18 Wiley-Blackwell

Using novel methods, this paper explores sources of uncertainty and gender bias in primary care doctors’ diagnostic decision-making about coronary heart disease (CHD). Claims about gendered consultation styles and quality of care are re-examined, along with the adequacy of CHD models for women. Randomly selected doctors in the UK and the US (n = 112, 56 per country, stratified by gender) were shown standardised videotaped vignettes of actors portraying patients with CHD. Patients’ age, gender, ethnicity and social class were varied systematically. During interviews, doctors gave free-recall accounts of their decision-making, which were analysed to determine patient and doctor gender effects. We found differences in male and female doctors’ responses to different types of patient information. Female doctors recall more patient cues overall, particularly about history presentation, and particularly amongst women. Male doctors appear less affected by patient gender but both male and especially female doctors take more account of male patients’ age, and consider more age-related disease possibilities for men than women. Findings highlight the need for better integration of knowledge about female presentations within accepted CHD risk models, and do not support the contention that women receive better-quality care from female doctors.

IP Marko, AR Adams, SJ Sweeney, ND Whitbread, AJ Ward, B Asplin, DJ Robbins (2007)The influence of carrier density non-pinning on the output power of 1.55 μm lasers at high temperature, In: Lasers and Electro-Optics, 2007 and the International Quantum Electronics Conferencepp. 1-1
BA Ikyo, IP Marko, AR Adams, SJ Sweeney, CL Canedy, I Vurgaftman, CS Kim, M Kim, WW Bewley, JR Meyer (2010)Temperature sensitivity of mid-infrared type II "W" interband cascade lasers (ICL) emitting at 4.1μm at room temperature, In: 22nd IEEE International Semi-conductor Laser Conferencepp. 41-42

The thermal properties of 5-stage “W” Interband-Cascade Lasers emitting at 4.1μm at RT are investigated. It is shown that inter-valence band absorption coupled with non-radiative recombination govern their maximum operating temperature.

Igor Marko, Alfred Adams, Stephen Sweeney, IR Sellers, DJ Mowbray, MS Skolnick, HY Liu, KM Groom (2004)Recombination and loss mechanisms in low-threshold InAs/GaAs 1.3 mu m quantum dot lasers, In: 2004 IEEE 19TH INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE, CONFERENCE DIGESTpp. 57-58

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

Timothy Eales, Igor Marko, BA Ikyo, Alfred Adams, S Arafin, S Sprengel, M-C Amann, Stephen Sweeney (2017)Wavelength dependence of efficiency limiting mechanisms in Type-I Mid-infrared GaInAsSb/GaSb lasers, In: IEEE Journal of Selected Topics in Quantum Electronics23(6) IEEE

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

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

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

NF Masse, SJ Sweeney, IP Marko, AR Adams, N Hatori, M Sugawara (2006)Temperature dependence of the gain in p-doped and intrinsic 1.3 mu m InAs/GaAs quantum dot lasers, In: APPLIED PHYSICS LETTERS89(19)ARTN 1pp. ?-? AMER INST PHYSICS
NF Masse, E Homeyer, IP Marko, AR Adams, SJ Sweeney, O Dehaese, R Piron, F Grillot, S Loualiche (2007)Temperature and pressure dependence of the recombination processes in 1.5 mu m InAs/InP (311)B quantum dot lasers, In: APPLIED PHYSICS LETTERS91(13)ARTN 1pp. ?-? AMER INST PHYSICS
MT Crowley, IP Marko, NF Masse, AD Andreev, S Tomic, SJ Sweeney, EP O'Reilly, AR Adams (2009)The Importance of Recombination via Excited States in InAs/GaAs 1.3 mu m Quantum-Dot Lasers, In: IEEE J SEL TOP QUANT15(3)pp. 799-807 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

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

JS Ng, WM Soong, MJ Steer, M Hopkinson, JPR David, J Chamings, SJ Sweeney, AR Adams (2007)Long wavelength bulk GaInNAs p-i-n photodiodes lattice matched to GaAs, In: JOURNAL OF APPLIED PHYSICS101(6)ARTN 0pp. ?-? AMER INST PHYSICS

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

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

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

IP Marko, SJ Sweeney, AR Adams, SR Jin, BN Murdin, R Schwertberger, A Somers, JP Reithmaier, A Forchel (2004)Recombination mechanisms in InAs/InP quantum dash lasers studied using high hydrostatic pressure, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH241(14)pp. 3427-3431
K O'Brien, S J Sweeney, A R Adams, B N Murdin, A Salhi, Y Rouillard, A Joullie (2006)Recombination Processes in Midinfrared InGaAsSb Diode Lasers Emitting at 2.37 mu m, In: Applied Physics Letters89(5)

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

AR Adams, RD Pollard, CM Snowden (1997)A method-of-moments study of strip dipole antennas in rectangular waveguide, In: IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES45(10)pp. 1756-1766 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
A Adams, CD Buckingham, S Arber, JB McKinlay, L Marceau, C Link (2006)The influence of patient's age on clinical decision-making about coronary heart disease in the USA and the UK, In: AGEING & SOCIETY26pp. 303-321 CAMBRIDGE UNIV PRESS
AR Adams, SJ Sweeney (2006)The physics controlling the sensitivity of semiconductor lasers to high temperatures, In: 2006 OPTICAL FIBER COMMUNICATION CONFERENCE/NATIONAL FIBER OPTIC ENGINEERS CONFERENCE, VOLS 1-6pp. 1631-1633
JS Ng, SL Tan, YL Goh, CH Tan, JPR David, J Allam, SJ Sweeney, AR Adams (2010)InGaAsN as absorber in APDs for 1.3 micron wavelength applicationspp. 187-190

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

T Higashi, SJ Sweeney, AF Phillips, AR Adams, EP O'Reilly, T Uchida, T Fujii (1999)Observation of reduced nonradiative current in 1.3-mu m AlGaInAs-InP strained MQW lasers, In: IEEE PHOTONICS TECHNOLOGY LETTERS11(4)pp. 409-411 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
SJ Sweeney, D McConville, NF Masse, RX Bouyssou, AR Adams, CN Ahmad, C Hanke (2004)Temperature and pressure dependence of recombination processes in 1.5 mu m InGaAlAs/InP-based quantum well lasers, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH241(14)pp. 3391-3398
JS Ng, WM Soong, MJ Steer, M Hopkinson, JPR David, J Chamings, AR Adams, SJ Sweeney, J Allam (2007)GaInNAs lattice-matched to GaAs for photodiodes, In: Conference Proceedings - International Conference on Indium Phosphide and Related Materialspp. 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.

SA Sayid, IP Marko, AR Adams, SJ Sweeney, P Barrios, P Poole (2010)Thermal behavior of 1.55 μm (100) InAs/InP-based quantum dot lasers, In: IEEE Poceeedings of 22nd International Semiconductor Laser Conferencepp. 75-76

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

AF Phillips, SJ Sweeney, AR Adams, PJA Thijs (1999)The temperature dependence of 1.3-and 1.5-mu m compressively strained InGaAs(P) MQW semiconductor lasers, In: IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS5(3)pp. 401-412 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
BA Ikyo, IP Marko, K Hild, AR Adams, SJ Sweeney, S Arafin, M-C Amann (2013)The effect of hole leakage and auger recombination on the temperature sensitivity of GaInAsSb/GaSb mid-infrared lasers, In: Lasers and Electro-Optics Europe (CLEO EUROPE/IQEC), 2013 Conference on and International Quantum Electronics Conference
D Lock, SJ Sweeney, AR Adams, S Deubner, F Klopf, JP Reithmaier, A Forchel (2004)Carrier leakage suppression utilising short-period superlattices in 980 nm InGaAs/GaAs quantum well lasers, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH241(14)pp. 3405-3409
SJ Sweeney, T Higashi, AR Adams, T Uchida, T Fujii (2000)A comparison of AlGaInAs and InGaAsP-based 1.3 mu m semiconductor lasers using high pressure, In: HIGH PRESSURE RESEARCH18(1-6)pp. 49-55
WM Soong, JS Ng, MJ Steer, M Hopkinson, JPR David, J Chamings, SJ Sweeney, AR Adams, J Allam (2008)Dark current mechanisms in bulk GaInNAs photodiodes, In: Proccedings of 20th International Conference on Indium Phosphide and Related Materials

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

K O'Brien, SJ Sweeney, AR Adams, BN Murdin, A Salhi, Y Rouillard, A Joullie (2006)Recombination processes in midinfrared InGaAsSb diode lasers emitting at 2.37 mu m, In: APPLIED PHYSICS LETTERS89(5)ARTN 0pp. ?-? AMER INST PHYSICS
SJ Sweeney, SR Jin, CN Ahmad, AR Adams, BN Murdin (2004)Carrier recombination processes in 1.3 mu m and 1.5 mu m InGaAs(P)-based lasers at cryogenic temperatures and high pressures, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH241(14)pp. 3399-3404
T Higashi, SJ Sweeney, AF Phillips, AR Adams, EP O'Reilly, T Uchida, T Fujii (1999)Experimental analysis of temperature dependence in 1.3-mu m AlGaInAs-InP strained MQW lasers, In: IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS5(3)pp. 413-419 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
J Chamings, S Ahmed, AR Adams, SJ Sweeney, VA Odnoblyudov, CW Tu, B Kunert, W Stolz (2009)Band anti-crossing and carrier recombination in dilute nitride phosphide based lasers and light emitting diodes, In: PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS246(3)pp. 527-531
S Tan, CJ Hunter, S Zhang, LJJ Tan, YL Goh, JS Ng, JPR David, Igor Marko, Stephen Sweeney, Alfred Adams, Jeremy Allam (2012)Improved optoelectronic properties of rapid thermally annealed dilute nitride GaInNAs photodetectors, In: Journal of Electronic Materials41(12)pp. 3393-3401 IEEE

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

R Fehse, SJ Sweeney, AR Adams, EP O'Reilly, AY Egorov, H Riechert, S Illek (2001)Insights into carrier recombination processes in 1.3 mu m GaInNAs-based semiconductor lasers attained using high pressure, In: ELECTRONICS LETTERS37(2)pp. 92-93 IEE-INST ELEC ENG
TE Sale, SJ Sweeney, G Knowles, AR Adams (2001)Gain-cavity alignment in efficient visible (660 nm) VCSELs studied using high pressure techniques, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH223(2)pp. 587-591 WILEY-V C H VERLAG GMBH
SL Tan, LJJ Tan, YL Goh, S Zhang, JS Ng, JPR David, IP Marko, J Allam, SJ Sweeney, AR Adams (2010)Reduction of dark current and unintentional background doping in InGaAsN photodetectors by ex situ annealing, In: Proceedings of SPIE - Posters Session7726

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

R Fehse, S Jin, SJ Sweeney, AR Adams, EP O'Reilly, H Riechert, S Illek, AY Egorov (2001)Evidence for large monomolecular recombination contribution to threshold current in 1.3 mu m GaInNAs semiconductor lasers, In: ELECTRONICS LETTERS37(25)pp. 1518-1520 IEE-INST ELEC ENG
J Chamings, AR Adams, SJ Sweeney, B Kunert, K Volz, W Stolz (2008)Temperature dependence and physical properties of Ga(NAsP)/GaP semiconductor lasers, In: APPLIED PHYSICS LETTERS93(10)ARTN 1pp. ?-? AMER INST PHYSICS
IP Marko, AD Andreev, AR Adams, R Krebs, JP Reithmaier, A Forchel (2003)Importance of Auger recombination in InAs 1.3 mu m quantum dot lasers, In: ELECTRONICS LETTERS39(1)pp. 58-59 IEE-INST ELEC ENG
AB Ikyo, IP Marko, AR Adams, SJ Sweeney, A Bachmann, K Kashani-Shirazi, M-C Amann (2009)Gain peak-cavity mode alignment optimisation in buried tunnel junction mid-infrared GaSb vertical cavity surface emitting lasers using hydrostatic pressure, In: IET OPTOELECTRONICS3(6)pp. 305-309
IP Marko, AR Adams, NF Massé, SJ Sweeney (2014)Effect of non-pinned carrier density above threshold in InAs quantum dot and quantum dash lasers, In: IET Optoelectronics8(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 μm. 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.

AR Adams, R Fehse, S Tomic, EP O'Reilly, A Andreev, G Knowles, TE Sale, SJ Sweeney, G Steinle, A Ramakrishnan, H Riechert (2002)Characterisation of 1.3pm wavelength GaInNAs/GaAs edge-emitting and vertical-cavity surface-emitting lasers using low-temperature and high-pressure, In: APOC 2002: ASIA-PACIFIC OPTICAL AND WIRELESS COMMUNICATIONS; MATERIALS AND DEVICES FOR OPTICAL AND WIRELESS COMMUNICATIONS4905pp. 183-197
SR Jin, SJ Sweeney, S Tomic, AR Adams, H Riechert (2003)Unusual increase of the Auger recombination current in 1.3 mu m GaInNAs quantum-well lasers under high pressure, In: APPLIED PHYSICS LETTERS82(14)pp. 2335-2337 AMER INST PHYSICS
SR Jin, R Fehse, SJ Sweeney, G Knowles, AR Adams, EP O'Reilly, H Reichert, S Illek, AY Egorov, PJA Thijs, T Uchida, T Fujii (2002)Modal refractive index of 1.3 mu m InGaAsP, AlGaInAs and GaInNAs semiconductor lasers under high hydrostatic pressure, In: ELECTRONICS LETTERS38(7)pp. 325-327 IEE-INST ELEC ENG
G Knowles, SJ Sweeney, TE Sale, AR Adams (2001)Self-heating effects in red (665 nm) VCSELs, In: IEE PROCEEDINGS-OPTOELECTRONICS148(5-6)PII 10.104pp. 256-260 IEE-INST ELEC ENG
SR Jin, Stephen Sweeney, S Tomic, Alfred Adams, H Riechert (2003)High-pressure studies of recombination mechanisms in 1.3-mu m GaInNAs quantum-well lasers, In: IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS9(5)pp. 1196-1201 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

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

I P Marko, A D Andreev, A R Adams, R Krebs, J P Reithmaier, A Forchel (2003)The Importance of Auger Recombination in InAs 1.3 um Quantum Dot Lasers, In: Electronics Letters58(59)

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

B. N. Murdin, A. R. Adams, P. Murzyn, C. R. Pidgeon, I. V. Bradley, J-P. R. Wells, Y. H. Matsuda, N. Miura, T. Burke, A. D. Johnson (2002)Band anticrossing in dilute InNxSb1–x, In: Applied Physics Letters256(2002)

Dilute nitrogen alloys of InSb exhibit extremely strong band gap bowing with nitrogen composition that has been associated with anticrossing between the localized resonant states of the nitrogen within the conduction band and the extended states of the conduction band itself. This also results in the conduction band dispersion having an enhanced nonparabolicity. We have measured the electron effective mass near the anticrossing by cyclotron resonance in InNxSb1–x alloys with absorption edge near 15 µm, using pulsed fields up to 150 T. The results directly demonstrate the band anticrossing and quantitatively confirm the increase of effective mass versus x predicted for InNxSb1–x by a tight binding calculation for low nitrogen concentration (x

R Fehse, AR Adams, SJ Sweeney, S Tomic, H Reichart, A Ramakrishnan (2003)Carrier recombination processes in MOVPE and MBE grown 1.3 mu m GaInNAs edge emitting lasers, In: SOLID-STATE ELECTRONICS47(3)pp. 501-506
IP Marko, AR Adams, SJ Sweeney, SR Jin, BN Murdin, R Schwertberger, A Somers, JP Reithmaier, A Forchel (2004)Experimental investigations into the thermal properties of 1.5-1.8-mu m InAs/InP quantum dash lasers, In: 2004 IEEE 19TH INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE, CONFERENCE DIGESTpp. 61-62
SR Jin, SJ Sweeney, AR Adams, T Higashi, H Riechert, PJA Thijs (2003)Wavelength dependence of the modal refractive index in 1.3 mu m InGaAsP, AlGaInAs and GaInNAs lasers using high pressure, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH235(2)pp. 491-495
R Fehse, S Tomic, AR Adams, SJ Sweeney, EP O'Reilly, A Andreev, H Riechert (2002)A quantitative study of radiative, Auger, and defect related recombination processes in 1.3-mu m GaInNAs-based quantum-well lasers, In: IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS8(4)pp. 801-810 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
IP Marko, AD Andreev, AR Adams, R Krebs, JP Reithmaier, A Forchel (2003)High-pressure studies of the recombination processes, threshold currents, and lasing wavelengths in InAs/GaInAs quantum dot lasers, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH235(2)pp. 407-411
JS Ng, WM Soong, MJ Steer, M Hopkinson, JPR David, J Chamings, SJ Sweeney, AR Adams (2007)Long wavelength bulk GaInNAs p-i-n photodiodes lattice matched to GaAs, In: JOURNAL OF APPLIED PHYSICS101(6)ARTN 0pp. ?-? AMER INST PHYSICS
SR Jin, SJ Sweeney, AR Adams, PJA Thijs (2003)Coupling of large optical loss with Auger recombination in 1.3 mu m InGaAsP lasers investigated using hydrostatic pressure, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH235(2)pp. 547-551
EP O'Reilly, S Fahy, A Lindsay, S Tomić, R Fehse, AR Adams, SJ Sweeney, AD Andreev, PJ Klar, H Grüning, H Riechert (2003)Novel electronic and optoelectronic properties of GaInNAs and related alloys, In: OSA Trends in Optics and Photonics Series88pp. 523-525

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

S. A. Choulis, A. Andreev, M. Merrick, A. R. Adams, B. N. Murdin, A. Krier, V. V. Sherstnev (2003)High-pressure measurements of mid-infrared electroluminescence from InAs light-emitting diodes at 3.3 µm, In: Applied Physics Letters1149(2003)

The spontaneous electroluminescence emission of InAs light-emitting diodes (LEDs) operating at 3.3 µm was studied as a function of applied hydrostatic pressure. An enhancement of a factor of almost four in radiative efficiency at room temperature was observed in the range 0 to 10 kbar. Analysis of the dependence of electroluminescence emission intensity on hydrostatic pressure at constant current reveals that nonradiative Auger recombination dominates the quantum efficiency of these LEDs.

B. N. Murdin, M. Kamal-Saadi, A. Lindsay, E. P. O'Reilly, A. R. Adams, G. J. Nott, J. G. Crowder, C. R. Pidgeon, I. V. Bradley, J-P. R. Wells, T. Burke, A. D. Johnson, T. Ashley (2001)Auger recombination in long-wavelength infrared InNxSb1–x alloys, In: Applied Physics Letters1568(2001)

Dilute nitrogen alloys of InSb exhibit strong band gap bowing with increasing nitrogen composition, shifting the absorption edge to longer wavelengths. The conduction band dispersion also has an enhanced nonparabolicity, which suppresses Auger recombination. We have measured Auger lifetimes in alloys with 11 and 15 µm absorption edges using a time-resolved pump-probe technique. We find the lifetimes to be longer at room temperature than equivalent band gap Hg1–yCdyTe alloys at the same quasi-Fermi level separation. The results are explained using a modified k·p Hamiltonian which explicitly includes interactions between the conduction band and a higher lying nitrogen-related resonant band.

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

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

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

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

SR Jin, SJ Sweeney, S Tomic, AR Adams, H Riechert (2003)Quantifying pressure-dependent recombination currents in GaInNAs lasers using spontaneous emission measurements, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH235(2)pp. 486-490
D Lock, SJ Sweeney, AR Adams, DJ Robbins (2003)Auger recombination in InGaAs/AlGaAs-based MQW semiconductor lasers emitting at 980 nm, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH235(2)pp. 542-546
S. R. Jin, S. J. Sweeney, C. N. Ahmad, A. R. Adams, B. N. Murdin (2004)Radiative and Auger recombination in 1.3 µm InGaAsP and 1.5 µm InGaAs quantum-well lasers measured under high pressure at low and room temperatures, In: Applied Physics Letters357(2004)

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

K O'Brien, AR Adams, SJ Sweeney, SR Jin, CN Ahmad, BN Murdin, CL Canedy, I Vurgaftman, JR Meyer (2006)Analysis of the major loss processes in mid-infrared type-II "W" diode lasers, In: Conference Digest - IEEE International Semiconductor Laser Conferencepp. 43-44

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

DJ DUNSTAN, RH DIXON, P KIDD, LK HOWARD, VA WILKINSON, JD LAMBKIN, C JEYNES, MP HALSALL, D LANCEFIELD, MT EMENY, PJ GOODHEW, KP HOMEWOOD, BJ SEALY, AR ADAMS (1993)GROWTH AND CHARACTERIZATION OF RELAXED EPILAYERS OF INGAAS ON GAAS, In: JOURNAL OF CRYSTAL GROWTH126(4)pp. 589-600 ELSEVIER SCIENCE BV
K. O'Brien, S. J. Sweeney, A. R. Adams, B. N Murdin, A. Salhi, Y. Rouillard, A. Joullié (2006)Recombination processes in midinfrared InGaAsSb diode lasers emitting at 2.37 µm, In: Applied Physics Letters051104(2006)

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

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

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

O von dem Knesebeck, M Boente, J Siegrist, L Marceau, C Link, S Arber, A Adams, J McKinlay (2008)Country differences in the diagnosis and management of coronary heart disease - a comparison between the US, the UK and Germany, In: BMC HEALTH SERVICES RESEARCH8ARTN 1pp. ?-? BIOMED CENTRAL LTD
SJ Sweeney, AF Phillips, AR Adams, EP O'Reilly, PJA Thijs (1998)Determination of the influence of Auger recombination on the threshold current of 1.3 μm and 1.5 μm InGaAs(P) strained-layer lasers and its variation with temperature, In: Conference Digest - IEEE International Semiconductor Laser Conferencepp. 63-64

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

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

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

Stephen Sweeney, D McConville, SR Jin, CN Ahmad, NF Masse, RX Bouyssou, Alfred Adams, C Hanke (2004)Temperature and wavelength dependence of recombination processes in 1.5 mu m InGaAlAs/InP-based lasers, In: 2004 International Conference on Indium Phosphide and Related Materials, Conference Proceedingspp. 738-741

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

SJ Sweeney, AF Phillips, AR Adams, EP O'Reilly, M Silver, PJA Thijs (1998)Transition from radiative to nonradiative recombination in 1.3-μm and 1.5-μm InGaAs(P) multiple quantum well semiconductor diode lasers, In: Conference on Lasers and Electro-Optics Europe - Technical Digestpp. 304-?

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

SJ Sweeney, AR Adams, EP O'Reilly, M Silver, PJA Thijs (2000)Effect of auger generated hot-holes on 1.5-μm InGaAs(P)-based quantum well semiconductor lasers, In: Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digestpp. 391-392

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

T Higashi, SJ Sweeney, AF Phillips, AR Adams, EP O'Reilly, T Uchida, T Fujii (1998)Observation of reduced non-radiative recombination current in 1.3-μm AlGaInAs/InP multiple-quantum-well lasers, In: Conference Digest - IEEE International Semiconductor Laser Conferencepp. 61-62

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

IP Marko, AR Adams, SJ Sweeney, NF Masse, R Krebs, JP Reithmaier, A Forchel, DJ Mowbray, MS Skolnick, HY Liu, KM Groom, N Hatori, M Sugawara (2007)Band gap dependence of the recombination processes in InAs/GaAs quantum dots studied using hydrostatic pressure, In: PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS244(1)pp. 82-86
D Lock, Stephen Sweeney, Alfred Adams (2003)Wavelength dependence of catastrophic optical damage threshold in 980nm semiconductor diode lasers, In: 2003 IEEE LEOS ANNUAL MEETING CONFERENCE PROCEEDINGS, VOLS 1 AND 2pp. 421-422

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

D Lock, SJ Sweeney, AR Adams (2004)Pressure induced wavelength dependence of catastrophic optical damage in 980 nm semiconductor diode lasers, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH241(14)pp. 3416-3419
SR Jin, CN Ahmad, SJ Sweeney, AR Adams, BN Murdin, H Page, X Marcadet, C Sirtori, S Tomic (2006)Spectroscopy of GaAs/AlGaAs quantum-cascade lasers using hydrostatic pressure, In: APPLIED PHYSICS LETTERS89(22)ARTN 2pp. ?-? AMER INST PHYSICS
MT Crowley, IP Marko, NF Masse, AD Andreev, SJ Sweeney, EP O'Reilly, AR Adams (2008)The importance of recombination via excited states in InAs/GaAs 1.3μm quantum dot lasers, In: IEEE Proceedings of 21st International Semiconductor Laser Conferencepp. 117-118

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.

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

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

SJ Sweeney, G Knowles, TE Sale, AR Adams (2001)Quantifying the effect of indirect carrier leakage on visible Al(GaInP) lasers using high pressures and low temperatures, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH223(2)pp. 567-572 WILEY-V C H VERLAG GMBH
S Tomic, EP O'Reilly, R Fehse, Stephen Sweeney, Alfred Adams, Aleksey Andreev, SA Choulis, Thomas Hosea, H Riechert (2003)Theoretical and experimental analysis of 1.3-mu m InGaAsN/GaAs lasers, In: IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS9(5)pp. 1228-1238 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

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

IP Marko, AR Adams, SJ Sweeney, R Teissier, AN Baranov, S Tomic (2008)Gamma-L scattering in InAs-based quantum cascade lasers studied using high hydrostatic pressure, In: 2008 IEEE 21ST INTERNATIONAL SEMICONDUCTOR LASER CONFERENCEpp. 47-48
AR Adams, RD Pollard, CM Snowden (1996)Method of moments and time domain analyses of waveguide-based hybrid multiple device oscillators, In: 1996 IEEE MTT-S INTERNATIONAL MICROWAVE SYMPOSIUM DIGEST, VOLS 1-3pp. 1255-1258
IP Marko, NF Masse, SJ Sweeney, AR Adams, N Hatori, M Sugawara, W Jantsch, F Schaffler (2007)Recombination, transport and loss mechanisms in p-doped InAs/GaAs quantum dots, In: Physics of Semiconductors, Pts A and B893pp. 837-838
IP Marko, AR Adams, SJ Sweeney, R Teissier, AN Baranov, S Tomic (2009)Evidence of carrier leakage into the L-valley in InAs-based quantum cascade lasers under high hydrostatic pressure, In: PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS246(3)pp. 512-515
LJJ Tan, WS Soong, SL Tan, YL Goh, MJ Steer, JS Ng, JPR David, IP Marko, J Chamings, J Allam, SJ Sweeney, AR Adams (2009)Dark current mechanisms in InxGa1-xAs 1-yNy, In: IEEE Proceedings of LEOS Annual Meeting Conferencepp. 233-234

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.

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

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

SJ Sweeney, DA Lock, AR Adams, J Menendez, CG VanDeWalle (2005)Carrier recombination in InGaAs(P) quantum well laser structures: Band gap and temperature dependence, In: Physics of Semiconductors, Pts A and B772pp. 1545-1546
I P Marko, A R Adams, S J Sweeney, S R Jin, B N Murdin, R Schwertberger, A Somers, J P Reithmaier, A Forchel (2004)Experimental Investigations into the Thermal Properties of 1.5-1.8μm InAs/InP Quantum Dash Lasers, In: 2004 IEEE 19th International Semiconductor Laser Conference, 2004. Conference Digest.

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

P BLOOD, ED FLETCHER, K WOODBRIDGE, KC HEASMAN, AR ADAMS (1989)INFLUENCE OF THE BARRIERS ON THE TEMPERATURE-DEPENDENCE OF THRESHOLD CURRENT IN GAAS ALGAAS QUANTUM WELL LASERS, In: IEEE JOURNAL OF QUANTUM ELECTRONICS25(6)pp. 1459-1468 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
S Tomić, R Fehse, SA Choulis, EP O'Reilly, AR Adams, SJ Sweeney, AD Andreev, TJC Hosea, H Riechert (2002)Experimental and theoretical analysis of the recombination processes in GaInNAs 1.3 μm Lasers, In: Conference Digest - IEEE International Semiconductor Laser Conferencepp. 41-42

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

G Knowles, R Fehse, S Tomić, SJ Sweeney, TE Sale, AR Adams, EP O'Reilly, G Steinle, H Riechert (2002)The temperature and pressure dependence of 1.3 μm GaInNAs vertical-cavity surface emitting lasers (VCSELs), In: Conference Digest - IEEE International Semiconductor Laser Conferencepp. 139-140

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

SJ Sweeney, AR Adams, M Silver, EP O'Reilly, JR Watling, AB Walker, PJA Thijs (1999)Dependence of threshold current on QW position and on pressure in 1.5 mu m InGaAs(P) lasers, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH211(1)pp. 525-531
AR Adams, M Silver, EP OReilly, B Gonul, AF Phillips, SJ Sweeney, PJA Thijs (1996)Hydrostatic pressure dependence of the threshold current in 1.5 mu m strained quantum well lasers, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH198(1)pp. 381-388
S. R. Jin, C. N. Ahmad, S. J. Sweeney, A. R. Adams, B. N. Murdin, H. Page, X. Marcadet, C. Sirtori, S. Tomić (2006)Spectroscopy of GaAs/AlGaAs quantum-cascade lasers using hydrostatic pressure, In: Applied Physics Letters221105(2006)
SJ Sweeney, AF Phillips, AR Adams, EP O'Reilly, PJA Thijs (1998)The effect of temperature dependent processes on the performance of 1.5-mu m compressively strained InGaAs(P) MQW semiconductor diode lasers, In: IEEE PHOTONICS TECHNOLOGY LETTERS10(8)pp. 1076-1078 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
AF Phillips, SJ Sweeney, AR Adams, PJA Thijs (1999)The hydrostatic pressure dependence of the threshold current in 1.3 mu m InGaAsP quantum well semiconductor diode lasers, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH211(1)pp. 513-518
SJ Sweeney, LJ Lyons, D Lock, AR Adams (2002)Direct measurement of facet temperature up to the melting point and COD in high power 980 nm semiconductor diode lasers, In: Conference Digest - IEEE International Semiconductor Laser Conferencepp. 161-162

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

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

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

SJ Sweeney, T Higashi, AR Adams, T Uchida, T Fujii (1998)Improved temperature dependence of 1.3 mu m AlGalnAs-based MQW semiconductor diode lasers revealed by hydrostatic pressure, In: ELECTRONICS LETTERS34(22)pp. 2130-2132 IEE-INST ELEC ENG
R Fehse, Stephen Sweeney, Alfred Adams, D McConville, H Riechert, L Geelhaar (2004)Influence of growth temperature on defect density in 1.3 mu m GaInNAs-based lasers, In: 2004 IEEE 19TH INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE, CONFERENCE DIGESTpp. 85-86

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

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

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

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

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

G Knowles, S Tomic, S Jin, R Fehse, SJ Sweeney, TE Sale, AR Adams (2003)Gain-cavity alignment profiling of 1.3 mu m emitting GaInNAs vertical cavity surface emitting lasers (VCSELs) using high pressure techniques, In: PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS235(2)pp. 480-485
Alfred Adams, Igor Marko, J Mukherjee, Stephen Sweeney, A Gocalinska, E Pelucchi, B Corbett (2014)Semiconductor quantum well lasers with a temperature insensitive threshold current, In: Conference Digest - IEEE International Semiconductor Laser Conferencepp. 82-83
CL Link, TA Stern, RS Piccolo, LD Marceau, S Arber, A Adams, J Siegrist, O von dem Knesebeck, JB McKinlay (2011)Diagnosis and Management of Depression in 3 Countries: Results From a Clinical Vignette Factorial Experiment., In: Primary Care Companion CNS Disord13(5) Physicians Posgraduates Press, Inc.

Objective: International differences in disease prevalence rates are often reported and thought to reflect different lifestyles, genetics, or cultural differences in care-seeking behavior. However, they may also be produced by differences among health care systems. We sought to investigate variation in the diagnosis and management of a "patient" with exactly the same symptoms indicative of depression in 3 different health care systems (Germany, the United Kingdom, and the United States).Method: A factorial experiment was conducted between 2001 and 2006 in which 384 randomly selected primary care physicians viewed a video vignette of a patient presenting with symptoms suggestive of depression. Under the supervision of experienced clinicians, professional actors were trained to realistically portray patients who presented with 7 symptoms of depression: sleep disturbance, decreased interest, guilt, diminished energy, impaired concentration, poor appetite, and psychomotor agitation or retardation.Results: Most physicians listed depression as one of their diagnoses (89.6%), but German physicians were more likely to diagnose depression in women, while British and American physicians were more likely to diagnose depression in men (P = .0251). American physicians were almost twice as likely to prescribe an antidepressant as British physicians (P = .0241). German physicians were significantly more likely to refer the patient to a mental health professional than British or American physicians (P < .0001). German physicians wanted to see the patient in follow-up sooner than British or American physicians (P < .0001).Conclusions: Primary care physicians in different countries diagnose the exact same symptoms of depression differently depending on the patient's gender. There are also significant differences between countries in the management of a patient with symptoms suggestive of depression. International differences in prevalence rates for depression, and perhaps other diseases, may in part result from differences among health care systems in different countries.

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

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

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

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

R Fehse, S Jin, SJ Sweeney, AR Adams, EP O'Reilly, S Illek, AY Egorov, H Riechert (2001)The temperature dependence of the recombination processes in 1.3 mu m GaInNAs-based edge emitting lasers, In: LEOS 2001: 14TH ANNUAL MEETING OF THE IEEE LASERS & ELECTRO-OPTICS SOCIETY, VOLS 1 AND 2, PROCEEDINGSpp. 330-331
KC HEASMAN, AR ADAMS, RG PLUMB (1987)SCANNING THE LASER GAIN SPECTRUM USING DISTRIBUTED FEEDBACK AND HYDROSTATIC-PRESSURE, In: ELECTRONICS LETTERS23(11)pp. 555-557 IEE-INST ELEC ENG
TR Konrad, CL Link, RJ Shackelton, LD Marceau, O von Dem Knesebeck, J Siegrist, S Arber, A Adams, JB McKinlay (2010)It's About Time Physicians' Perceptions of Time Constraints in Primary Care Medical Practice in Three National Healthcare Systems, In: Medical Care48(2)pp. 95-100 American Public Health Association

Background: As physicians are pressured to deliver an increasing number of preventive services, follow guidelines, engage in evidence-based practice, and deliver patient-centered care in managerially driven organizations, they struggle with how much control they have over their time. Methods: A secondary analysis was conducted with data from 3 parallel studies of clinical decision making in Germany, the United Kingdom, and the United States with 128 physicians per country. Physicians reported how much time they were allocated and how much time they needed for high-quality care for new patient appointments, routine consultations, and complete physicals. They also reported how much control they had over their time in the office and spending adequate time with patients. Results: German, British, and American physicians were allocated (on average) 16/11/32 minutes for a new patient appointment, 6/10/18 minutes for a routine visit, and 12/20/36 minutes for a complete physical, but felt that they needed more time. Over half of German and American physicians felt that they always or usually had control over the hours they were required to be in their office or spending sufficient time with their patients while less than half of British physicians felt this way. Conclusion: German physicians had the least time allocated and needed for most types of appointment. American physicians had the most time allocated and needed for each type of appointment. However, British physicians felt they had the least control over time in their office and spending sufficient time with patients.

SL Tan, WM Soong, JE Green, MJ Steer, S Zhang, LJJ Tan, JS Ng, IP Marko, SJ Sweeney, AR Adams, J Allam, JPR David (2013)Experimental evaluation of impact ionization in dilute nitride GaInNAs diodes, In: APPLIED PHYSICS LETTERS103(10)ARTN 1pp. ?-? AMER INST PHYSICS
BG Crutchley, IP Marko, AR Adams, SJ Sweeney (2010)Efficiency limitations of green InGaN LEDs and laser diodes, In: 22nd IEEE International Semiconductor Laser Conferencepp. 27-28
R Fehse, SJ Sweeney, AR Adams, D McConville, H Riechert, L Geelhaar (2004)Influence of growth temperature on carrier recombination in GaInNAs-based lasers, In: IEE PROCEEDINGS-OPTOELECTRONICS151(5)pp. 447-451
SR Jin, SJ Sweeney, CN Ahmad, AR Adams, BN Murdin (2004)Radiative and Auger recombination in 1.3 mu m InGaAsP and 1.5 mu m InGaAs quantum-well lasers measured under high pressure at low and room temperatures, In: APPLIED PHYSICS LETTERS85(3)pp. 357-359 AMER INST PHYSICS
SL Tan, S Zhang, WM Soong, YL Goh, LJJ Tan, JS Ng, JPR David, IP Marko, AR Adams, SJ Sweeney, J Allam (2011)GaInNAsSb/GaAs Photodiodes for Long-Wavelength Applications, In: IEEE ELECTRON DEVICE LETTERS32(7)pp. 919-921 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
BA Ikyo, IP Marko, AR Adams, SJ Sweeney, CL Canedy, I Vurgaftman, CS Kim, M Kim, WW Bewley, JR Meyer (2011)Temperature dependence of 4.1 mu m mid-infrared type II "W" interband cascade lasers, In: APPLIED PHYSICS LETTERS99(2)ARTN 0pp. ?-? AMER INST PHYSICS
SJ Sweeney, T Higashi, A Andreev, AR Adams, T Uchida, T Fujii (2001)Superior temperature performance of 1.3 mu m AlGaInAs-Based semiconductor lasers investigated at high pressure and low temperature, In: PHYSICA STATUS SOLIDI B-BASIC RESEARCH223(2)pp. 573-579 WILEY-V C H VERLAG GMBH
G Knowles, R Fehse, S Tomic, Stephen Sweeney, TE Sale, Alfred Adams, P O'Reilly, G Steinle, H Riechert (2003)Investigation of 1.3-mu m GaInNAs vertical-cavity surface-emitting lasers (VCSELs) using temperature, high-pressure, and modelling techniques, In: IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS9(5)pp. 1202-1208 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

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

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.

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

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

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

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

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

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

IP Marko, AD Andreev, SJ Sweeney, AR Adams, R Krebs, S Deubert, JP Reithmaier, A Forchel, J Menendez, CG VanDeWalle (2005)The influence of auger processes on recombination in long-wavelength InAs/GaAs quantum dots, In: Physics of Semiconductors, Pts A and B772pp. 681-682
SJ Sweeney, SR Jin, S Tomic, AR Adams, T Higashi, H Riechert, PJA Thijs (2003)Hydrostatic pressure dependence of recombination mechanisms in GaInNAs, InGaAsP and AlGaInAs 1.3 mu m quantum well lasers, In: PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS235(2)pp. 474-479
D Lock, SJ Sweeney, AR Adams (2003)Fundamental limitations of high power 980nm InGaAs/GaAs pump lasers, In: 2003 IEEE LEOS ANNUAL MEETING CONFERENCE PROCEEDINGS, VOLS 1 AND 2pp. 427-428
KC Heasman, EP O'Reilly, GP Witchlow, W Batty, AR Adams (1987)Proposal For A Low Threshold Current Long Wavelength Strained Layer Laser, In: Novel Optoelectronic Devices
P Marko, AR Adams, SJ Sweeney, ND Whitbread, AJ Ward, B Asplin, J Robbins (2007)The influence of carrier density non-pinning on the output power of 1.55 μm lasers at high temperature, In: Optics InfoBase Conference Papers
KC Heasman, EP O'Reilly, AR Adams (1989)Characterization and Design of Semiconductor Lasers Using Strain, In: NATO ASI Series189pp. 279-301 Springer New York
BN Murdin, AR Adams, SJ Sweeney (2006)Band structure and high-pressure measurements, In: Springer Series in Optical Sciences118pp. 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 2.37μm at atmospheric pressure. Clearly high-pressure techniques provide exciting opportunities for the study of mid-infrared devices. © 2006 Springer-Verlag London Limited.

DG McConville, SJ Sweeney, AR Adams, S Tomic, H Riechert (2007)Temperature and pressure dependence of the recombination mechanisms in 1.3 pm and 1.5 pm GaInNAs lasers, In: PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS244(1)pp. 208-212
Igor Marko, Alfred Adams, Stephen Sweeney, DJ Mowbray, MS Skolnick, HYY Liu, KM Groom (2005)Recombination and loss mechanisms in low-threshold InAs-GaAs 1.3-mu m quantum-dot lasers, In: IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS11(5)pp. 1041-1047 IEEE

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

Igor Marko, N Masse, SJ Sweeney, AR Adams, IR Sellers, DJ Mowbray, MS Skolnick, HY Liu, KM Groom (2005)Effect of gain saturation and nonradiative recombination on the thermal characteristics of InAs/GaAs 1.3 mu m quantum dot lasers, In: The 18th Annual Meeting of the IEEE Lasers and Electro-Optics Society, 2005. (LEOS 2005)pp. 401-402 IEEE

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

K O'Brien, AR Adams, SJ Sweeney, SR Jin, CN Ahmad, BN Murdin, CL Canedy, I Vurgaftman, JR Meyer (2007)High pressure studies of mid-infrared type-II "W" diode lasers at cryogenic temperatures, In: PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS244(1)pp. 224-228
KE Lutfey, C Link, C Marceau, RW Grant, A Adams, S Arber, J Siegrist, O Bonte. M, J von dem Knesebeck, McKinlay (2009)Diagnostic Certainty as a Source of Medical Practice Variation in Coronary Heart Disease: Results from a Cross-National Experiment of Clinical Decision Making, In: Medical Decision Making29(5)pp. 606-618 Sage Publications

The authors examined physician diagnostic certainty as one reason for cross-national medical practice variation. Data are from a factorial experiment conducted in the United States, the United Kingdom, and Germany, estimating 384 generalist physicians’ diagnostic and treatment decisions for videotaped vignettes of actor patients depicting a presentation consistent with coronary heart disease (CHD). Despite identical vignette presentations, the authors observed significant differences across health care systems, with US physicians being the most certain and German physicians the least certain (P < 0.0001). Physicians were least certain of a CHD diagnoses when patients were younger and female (P < 0.0086), and there was additional variation by health care system (as represented by country) depending on patient age (P < 0.0100) and race (P < 0.0021). Certainty was positively correlated with several clinical actions, including test ordering, prescriptions, referrals to specialists, and time to follow-up.

S Arber, J McKinlay, A Adams, L Marceau, C Link, A O'Donnell (2007)Patient characteristics and inequalities in doctors’ diagnostic and management strategies in relation to CHD: A video-simulation experiment, In: Social Science & Medicine62(1)pp. 103-115 Elsevier

Numerous studies examine inequalities in health by gender, age, class and race, but few address the actions of primary care doctors. This factorial experiment examined how four patient characteristics impact on primary care doctors’ decisions regarding coronary heart disease (CHD). Primary care doctors viewed a video-vignette of a scripted consultation where the patient presented with standardised symptoms of CHD. Videotapes were identical apart from varying patients’ gender, age (55 versus 75), class and race, thereby removing any confounding factors from the social context of the consultation or other aspects of patients’ symptomatology or behaviour. A probability sample of 256 primary care doctors in the UK and US viewed these video-vignettes in a randomised experimental design. Gender of patient significantly influenced doctors’ diagnostic and management activities. However, there was no influence of social class or race, and no evidence of ageism in doctors’ behaviour. Women were asked fewer questions, received fewer examinations and had fewer diagnostic tests ordered for CHD. ‘Gendered ageism’ was suggested, since midlife women were asked fewest questions and prescribed least medication appropriate for CHD. Primary care doctors’ behaviour differed significantly by patients’ gender, suggesting doctors’ actions may contribute to gender inequalities in health.

K O'Brien, SJ Sweeney, AR Adams, SR Jin, CN Ahmad, BN Murdin, A Salhi, Y Rouillard, A Joullie (2007)Carrier recombination mechanisms in mid-infrared GaInAsSb quantum well lasers, In: PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS244(1)pp. 203-207

Hydrostatic pressure and spontaneous emission techniques have been used to examine the important recombination mechanisms in type-I GaInAsSb/GaSb quantum well lasers. High pressure results indicate that Auger recombination dominates the threshold current of 2.11 mu m and 2.37 mu m devices and is the origin of their temperature sensitivity around room temperature. While the characteristics of the 2.37 mu m devices are much improved by the suppression of the CHSH Auger process, since its spin-orbit splitting energy is greater than its band gap, other important Auger processes such as CHHL and CHCC persist. In the larger band gap 2.11 mu m devices, an increase in threshold current with pressure is observed suggesting that CHSH Auger is present in these devices at atmospheric pressure and contributes to performance degradation at these shorter wavelengths.

AR Adams, KC Heasman, J Hilton (1987)A reassessment of intervalence band absorption in 1.6μm (GaIn)(AsP)/InP, In: Semiconductor Science and Technology2(12)pp. 761-764

In the paper the authors re-evaluate the influence of intervalence band absorption on the temperature sensitivity of 1.6 mu m (GaIn)(AsP)/InP lasers and emphasise its general importance in semiconductor lasers operating at several times their threshold current.

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

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

KC HEASMAN, AR ADAMS, PD GREENE, GD HENSHALL (1987)PRESSURE-DEPENDENCE OF THRESHOLD CURRENT AND CARRIER LIFETIME IN 1.55-MU-M GAINASP LASERS, In: ELECTRONICS LETTERS23(10)pp. 492-493 IEE-INST ELEC ENG
KC HEASMAN, J HAYES, AR ADAMS, PD GREENE (1981)TEMPERATURE-DEPENDENCE OF THE TRANSFERRED ELECTRON THRESHOLD CURRENTIN IN1-XGAXASYP1-Y, In: ELECTRONICS LETTERS17(20)pp. 756-757 IEE-INST ELEC ENG
KC HEASMAN, P BLOOD, AR ADAMS, ED FLETCHER (1987)PRESSURE-DEPENDENCE OF THE NONRADIATIVE LIFETIME IN GAAS/AIGAAS DOUBLE-HETEROSTRUCTURE LASERS, In: JOURNAL OF APPLIED PHYSICS62(8)pp. 3448-3450 AMER INST PHYSICS
EP OREILLY, KC HEASMAN, AR ADAMS, GP WITCHLOW (1987)CALCULATIONS OF THE THRESHOLD CURRENT AND TEMPERATURE SENSITIVITY OF A (GAIN)AS STRAINED QUANTUM-WELL LASER OPERATING AT 1.55 MU-M, In: SUPERLATTICES AND MICROSTRUCTURES3(2)pp. 99-102 ACADEMIC PRESS LTD
J Chamings, AR Adams, SJ Sweeney, B Kunert, K Volz, W Stolz (2008)Thermal properties of Silicon compatible GaNAsP SQW lasers, In: 2008 IEEE 21ST INTERNATIONAL SEMICONDUCTOR LASER CONFERENCEpp. 61-62
J McKinlay, C Link, S Arber, L Marceau, A O'Donnell, A Adams (2006)How do doctors in different countries manage the same patient? Results of a factorial experiment, In: Health Services Research41(6)pp. 2182-2200 Blackwell Publishing

Objective. To determine the relative contributions of: (1) patient attributes; (2) provider characteristics; and (3) health care systems to health care disparities in the management of coronary heart disease (CHD) and depression. Data Sources/Study Setting. Primary experimental data were collected in 2001–2 from 256 randomly sampled primary care providers in the U.S. (Massachusetts) and the U.K. (Surrey, Southeast London, and the West Midlands). Study Design. Two factorial experiments were conducted in which physicians were shown, in random order, two clinically authentic videotapes of “patients” presenting with symptoms strongly suggestive of CHD and depression. “Patient” characteristics (age, gender, race, and socioeconomic status [SES]) were systematically varied, permitting estimation of unconfounded main effects and the interaction of patient, provider, and system-level influences. Data Collection/Data Extraction Methods. Analysis of variance was used to measure provider decision-making outcomes, including diagnosis, information seeking, test ordering, prescribing behavior, lifestyle recommendations, and referrals/follow-ups. Principal Findings. There is a high level of consistency in decision making for CHD and depression between the U.S. and the U.K. Most physicians in both countries correctly identified conditions depicted in the vignettes, although U.S. doctors engage in more information seeking, are more likely to prescribe medications, and are more certain of their diagnoses than their U.K. counterparts. The absence of any national differences in test ordering is consistent for both of the medical conditions depicted. U.K. physicians, however, were more likely than U.S. physicians to make lifestyle recommendations for CHD and to refer those patients to other providers. Conclusions. Substantively, these findings point to the importance of patient and provider characteristics in understanding between-country differences in clinical decision making. Methodologically, our use of a factorial experiment highlights the potential of these methods for health services research—especially the estimation of the influence of patient attributes, provider characteristics, and between-country differences in the quality of medical care.

JB Moore, A Adams, EL Molloy, S O'Dea (2007)BMP2 and BMP4 differentially modulate extracellular matrix-related gene expression in human lung epithelial cells, In: FASEB JOURNAL21(5)pp. A248-A248
R Fehse, I Marko, AR Adams (2003)Long wavelength lasers on GaAs substrates, In: IEE PROCEEDINGS-CIRCUITS DEVICES AND SYSTEMS150(6)pp. 521-528
IP Marko, AD Andreev, AR Adams, R Krebs, JP Reithmaier, A Forchel (2003)Auger recombination in 1.3-μm InAs/GaInAs quantum dot lasers studied using high pressure, In: Conference on Lasers and Electro-Optics Europe - Technical Digestpp. 175-175

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