Professor Stephen Sweeney

Professor of Physics, EPSRC Leadership Fellow, Head of Photonics group

Qualifications: BSc (Bath) CertEd (Bath) PhD (Surrey) QTS CPhys FInstP SenMIEEE

Email:
Phone: Work: 01483 68 9406
Room no: 12 ATI 01

Office hours

12ATI01 (Email for appointments)

Further information

Research Interests

Stephen's primary research interests lie in the area of semiconductor materials for photonic devices. He has produced >300 journal papers and conference proceedings in this area including several invited papers. He has also published >10 patents and 5 book chapters in the field of photonics. 

Recent research topics include:

  • novel semiconductor alloys such as bismides and nitrides for high efficiency photonic devices
  • silicon compatible lasers for future optical computing
  • semiconductor lasers for temperature insensitive operation (quantum dots, dilute-nitrides etc)
  • widely tunable lasers
  • vertical cavity surface emitting lasers and LEDs for plastic fibre systems
  • semiconductor lasers for optical pumping (EDFA, Raman) and printing and data storage applications
  • using photonic devices to sense chemical and biological samples (liquids and gases)

Information about currently available PhD projects can be found here

Research Collaborations

Stephen collaborates with a wide range of international partners in both academia and industry, as can be seen from his publications list.

Publications

Highlights

  • 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) Article number ARTN 115104
  • 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)

    Abstract

    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 (E), the spin-orbit splitting energy (Δ), 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 Δ > E 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 Δ > E, 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, Sweeney SJ, Petropoulos JP, Zhong Y, Dongmo PB, Zide JMO. (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)

    Abstract

    Replacing small amounts of As with Bi in InGaBiAs/InP induces large decreases and increases in the bandgap, E, and spin-orbit splitting, Δ, respectively. The possibility of achieving Δ > E and a reduced temperature (T) dependence for E are significant for suppressing recombination losses and improving performance in mid-infrared photonic devices. We measure E (x, T) and Δ (x, T) in InGa BiAs/InP samples for 0 x 0.039 by various complementary optical spectroscopic techniques. While we find no clear evidence of a decreased dE/dT (≈0.34 ± 0.06 meV/K in all samples) we find Δ > E for x > 3.3-4.3. The predictions of a valence band anti-crossing model agree well with the measurements. © 2012 American Institute of Physics.

  • 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) Article number ARTN 011107
  • 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) Article number ARTN 113108
  • 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.

    Abstract

    We report modulation of the absorption coefficient at 1.3 μm 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.

  • 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) Article number ARTN 071110
  • 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) Article number ARTN 071109
  • 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) Article number ARTN 021102
  • 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) Article number ARTN 122107
  • 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) Article number ARTN 161104

Journal articles

  • Marko IP, Bushell ZL, Jin SR, Hild K, Batool Z, Sweeney SJ, Ludewig P, Reinhard S, Nattermann L, Stolz W, Volz K. (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)

    Abstract

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

  • 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.
  • Mohmad AR, Bastiman F, Hunter CJ, Richards RD, Ng JS, David JPR, Majlis BY, Sweeney SJ. (2014) 'Localization effects and band gap of GaAsBi alloys'. Physica Status Solidi (B) Basic Research, 251 (6), pp. 1276-1281.

    Abstract

    The structural and optical properties of GaAsBi 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 GaAsBi 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, P was increased from 0.11 to 1140Wcm, 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 GaAsBi 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 GaAsBi for x up to 0.108 has been plotted and compared with the literature. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  • 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) Article number ARTN 013102
  • Jarvis SD, Mukherjee J, Sweeney SJ, Perren M. (2014) 'Development and characterisation of laser power converters for optical power transfer applications'. IET Optoelectronics, 8 (2), pp. 64-70.

    Abstract

    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 μm (which is eye and skin safe up to a power density of 1 kW/m) 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 μm and 1 kW/m, 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 μm and 1 kW/m. © The Institution of Engineering and Technology 2014.

  • 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.

    Abstract

    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.

  • 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)

    Abstract

    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 μm) on conventional InP substrates. We also show how bismuth may be used to form alloys whereby the spin-orbit splitting energy (Δ) is large and controllable and can, for example, be made larger than the band gap (E) 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.

  • 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.

    Abstract

    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.

  • Tan SL, Soong WM, Green JE, Steer MJ, Zhang S, Tan LJJ, Ng JS, David JPR, Marko IP, Sweeney SJ, Adams AR, Allam J. (2013) 'Experimental evaluation of impact ionization in dilute nitride GaInNAs diodes'. Applied Physics Letters, 103 (10)

    Abstract

    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 = β/α, is enhanced by a factor up to ∼4 with increasing nitrogen content. The absolute ionization coefficients are suppressed by up to two orders of magnitude at low electric fields in samples with 3% N. The narrow band gap, suppressed impact ionization, and increased breakdown voltage characteristics of GaInNAs make it a suitable material for use as part of a composite collector in GaAs-based heterojunction bipolar transistors. © 2013 AIP Publishing LLC.

  • Pal J, Migliorato MA, Li C-K, Wu Y-R, 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)

    Abstract

    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.

  • Mukherjee J, Jarvis S, Sweeney SJ, Perren M. (2013) 'Efficiency limits of laser power converters for optical power transfer applications'. Journal of Physics D: Applied Physics, 46 (26)

    Abstract

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

  • Ludewig P, Knaub N, Reinhard S, Nattermann L, Chatterjee S, Stolz W, Volz K, Hossain N, Marko IP, Jin SR, Hild K, Sweeney SJ. (2013) 'Electrical injection Ga(AsBi)/(AlGa)As single quantum well laser'. Applied Physics Letters, 102 (24)

    Abstract

    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/cm at an emission wavelength of ∼947 nm. These results from broad area devices show great promise for developing efficient IR laser diodes based on this emerging materials system. © 2013 AIP Publishing LLC.

  • Aldukhayel A, Jin SR, Marko IP, Sweeney SJ, Zhang SY, Revin DG, Cockburn JW. (2013) 'Investigations of carrier scattering into L-valley in λ=3.5μm InGaAs/AlAs(Sb) quantum cascade lasers using high hydrostatic pressure'. Physica Status Solidi (B) Basic Research, 250 (4), pp. 693-697.

    Abstract

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

  • Crutchley BG, Marko IP, Sweeney SJ, Pal J, Migliorato MA. (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.

    Abstract

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

  • 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) Article number ARTN 115104
  • 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)

    Abstract

    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 (E), the spin-orbit splitting energy (Δ), 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 Δ > E 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 Δ > E, 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.

  • Hossain N, Hild K, Jin SR, Sweeney SJ, Yu S-Q, Johnson SR, Ding D, Zhang Y-H. (2013) 'The influence of growth conditions on carrier recombination mechanisms in 1.3 μm GaAsSb/GaAs quantum well lasers'. Applied Physics Letters, 102 (4)

    Abstract

    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/QW to 138 Acm/QW and the characteristic temperature, T (T), from 51 ± 5 K (104 ± 16 K) to 62 ± 2 K (138 ± 7 K) near room temperature. © 2013 American Institute of Physics.

  • 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)

    Abstract

    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.

  • Maspero R, Sweeney SJ, Florescu M. (2013) 'Modelling the Auger Recombination rates of GaAsBi alloys'. 13th International Conference on Numerical Simulation of Optoelectronic Devices, NUSOD 2013, , pp. 81-82.

    Abstract

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

  • 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.

    Abstract

    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.

  • 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.
  • Batool Z, Hild K, Hosea TJC, Jin S, Sweeney SJ, Chatterjee S, Chernikov A, Fritz R, Koch M, Koch SW, Kolata K, Volz K, Duzik A, Millunchick JM, Thomas JC, Gogineni C, Johnson SR, Lu X, Riordan NA, Imhof S, Thränhardt A, Jiang Z, Mooney PM, Lewis RB, Masnadi-Shirazi M, Tiedje T, Rubel O. (2013) 'Bismuth-containing III-V semiconductors: Epitaxial growth and physical properties'. Molecular Beam Epitaxy, , pp. 139-158.
  • 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.

    Abstract

    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.

  • Jarvis S, Mukherjee J, Sweeney SJ, Perren M. (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.

    Abstract

    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 μm illumination at 1 kW/m 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.

  • 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)
  • Mukherjee J, Sweeney SJ, Wulfken W, Hartje H, Steinsiek F, Perren M. (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.

    Abstract

    We report on the successful demonstration of terrestrial laser power beaming across a distance of 30 m at an eye-safe wavelength of 1550 nm. Using novel photovoltaic convertors based on III-V semiconductors an optical to electrical power conversion efficiency of 45±1 % at 1 kW/m 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.

  • Lock DA, Prins AD, Crutchley BG, Kynaston S, Sweeney SJ, Hall SRG. (2013) 'LED junction temperature measurement using generated photocurrent'. IEEE/OSA Journal of Display Technology, 9 (5), pp. 396-401.

    Abstract

    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.

  • 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, 41 (12), pp. 3393-3401.

    Abstract

    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.

  • Marko IP, Batool Z, Hild K, Jin SR, Hossain N, Hosea TJC, Sweeney SJ, Petropoulos JP, Zhong Y, Dongmo PB, Zide JMO. (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)

    Abstract

    Replacing small amounts of As with Bi in InGaBiAs/InP induces large decreases and increases in the bandgap, E, and spin-orbit splitting, Δ, respectively. The possibility of achieving Δ > E and a reduced temperature (T) dependence for E are significant for suppressing recombination losses and improving performance in mid-infrared photonic devices. We measure E (x, T) and Δ (x, T) in InGa BiAs/InP samples for 0 x 0.039 by various complementary optical spectroscopic techniques. While we find no clear evidence of a decreased dE/dT (≈0.34 ± 0.06 meV/K in all samples) we find Δ > E for x > 3.3-4.3. The predictions of a valence band anti-crossing model agree well with the measurements. © 2012 American Institute of Physics.

  • 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)

    Abstract

    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.

  • Blume G, Hild K, Marko IP, Hosea TJC, Sweeney SJ, Yu S-Q, Chaparro SA, Samal N, Johnson SR, Zhang Y-H. (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)

    Abstract

    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 μm 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.

  • 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) Article number ARTN 012106
  • 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) Article number ARTN 011107
  • 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) Article number ARTN 113108
  • 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) Article number ARTN 051105
  • 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.

    Abstract

    Bi acts as a surfactant in molecular beam epitaxy (MBE) growth on GaAs(100). Incorporation is achieved by disequilibrium at growth temperatures below ∼450 °C. Bi can however affect the static reconstruction up to 600 °C. Two reconstructions are considered in this work: dynamic (2×1) and static c(8×3)/(4×3), which are shown to be the dominant reconstructions for GaAsBi MBE. Bi storage in these two reconstructions provides an explanation of RHEED transitions that cause unintentional Biincorporation in the GaAs capping layer. Finally dynamic observations of the (2×1) reconstruction are used to explain growth dynamics, atomic ordering and clustering observed in GaAsBi epilayers which have a direct influence on photoluminescence linewidth broadening in mixed anion III–V alloys.

  • Sweeney SJ. (2012) 'Bismide alloys for photonic devices: Potential and progress'. 2012 IEEE Photonics Conference, IPC 2012, , pp. 602-603.

    Abstract

    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.

  • 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.

    Abstract

    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.

  • 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.

    Abstract

    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.

  • Buaprathoom S, Prins AD, Sweeney SJ, Pedley S. (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

    Abstract

    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 μm and 3.0μm 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 and 1.2×10 particles/ml for 1.1 μm and 3.0 μm in mono-dispersed solutions and 2.3 % and 3.5% relating to references' concentrations of 1.1×10 and 4.4×10 particles/ml for 1.1 μm and 3.0 μm 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.

  • 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.

    Abstract

    The absorption properties of a series of GaAsBi /GaAs layers with ∼ Bi have been systematically investigated by measuring photocurrent spectra in p-i-n diode structures grown by molecular beam epitaxy. The GaAsBi/GaAs layers varied in thickness from 50 to 350 nm and showed a photoresponse in the near-infrared up to almost 1.3 μ. The absorption coefficients of the layers were obtained from the responsivity data. Below the band gap, the absorption coefficients showed an exponential dependence on the photon energy (Urbach tailing). © 1989-2012 IEEE.

  • 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

    Abstract

    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.

  • 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.
  • Reed GT, Thomson DJ, Gardes FY, Hu Y, Owens N, Yang X, Petropoulos P, 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 G-H, Le Liepvre A, Jany C, Lamponi M, Make D, Lelarge F, Fedeli JM, Messaoudene S, Keyvaninia S, Roelkens G, Van Thourhout D, Liu S. (2012) 'High performance silicon optical modulators'. Proceedings of SPIE - The International Society for Optical Engineering, 8564

    Abstract

    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.

  • 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.

    Abstract

    We report modulation of the absorption coefficient at 1.3 μm 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.

  • 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) Article number ARTN 141110
  • 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) Article number ARTN 071109
  • 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) Article number ARTN 071110
  • 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.
  • 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) Article number ARTN 042107
  • 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) Article number ARTN 021102
  • 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.
  • Sweeney S. (2011) 'Selected papers from the Semiconductor and Integrated Optoelectronics (SIOE'10) Conference'. IET OPTOELECTRONICS, 5 (3), pp. 99-99.
  • 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) Article number ARTN 122107
  • 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) Article number ARTN 063101
  • 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) Article number ARTN 105103
  • 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.

    Abstract

    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.

  • Ongrai O, Pearce JV, Machin G, Sweeney SJ. (2011) 'Miniature Co-C eutectic fixed-point cells for self-validating thermocouples'. MEASUREMENT SCIENCE & TECHNOLOGY, 22 (1) Article number ARTN 015104
  • 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) Article number ARTN 161104
  • 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.
  • Pearce JV, Ongrai O, Machin G, Sweeney SJ. (2010) 'Self-validating thermocouples based on high temperature fixed points'. METROLOGIA, 47 (1), pp. L1-L3.
  • Marko IP, Aldukhayel AM, Adams AR, Sweeney SJ, Teissier R, Baranov AN, Tomić S. (2010) 'Physical properties of short wavelength 2.6μm InAs/AlSb-based quantum cascade lasers'. Conference Digest - IEEE International Semiconductor Laser Conference, , pp. 95-96.

    Abstract

    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.

  • 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.

    Abstract

    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.

  • Hossain N, Jin SR, Sweeney SJ, Liebich S, Ludewig P, Zimprich M, Volz K, Stolz W, Kunert B. (2010) 'On the temperature dependence of monolithically integrated Ga(NAsP)/(BGa)P/Si QW lasers'. Optics InfoBase Conference Papers,

    Abstract

    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.

  • 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.
  • 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.
  • Sweeney S. (2009) 'Why not do both?'. Physics World, 22 (12), pp. 44-45.
  • 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 Article number ARTN 09013
  • 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.
  • 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, London, ENGLAND: 20, pp. 272-276.

    Abstract

    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.

  • Sharma TK, Hosea TJC, Sweeney SJ, Tang X. (2008) 'An accurate determination of the electronic transitions of InAs/InGaAs/InP quantum dots for midinfrared lasers using simultaneous complementary spectroscopic techniques'. JOURNAL OF APPLIED PHYSICS, 104 (8) Article number ARTN 083109
  • 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) Article number ARTN 101108
  • 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) Article number ARTN 021101
  • 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) Article number ARTN 131113
  • Coote J, Sweeney SJ. (2007) 'Semiconductor lasers as integrated optical biosensors: Sensitivity optimisation'. Journal of Physics: Conference Series, 76 (1)

    Abstract

    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.

  • Masse NF, Adams AR, Sweeney SJ. (2007) 'Experimental determination of the band gap dependence of Auger recombination in InGaAs/InP multiple quantum well lasers at room temperature'. APPLIED PHYSICS LETTERS, 90 (16) Article number ARTN 161113
  • 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) Article number ARTN 064506
  • Bueckers C, Blume G, Thraenhardt A, Schlichenmaier C, Klar PJ, Weiser G, Koch SW, Hader J, Moloney JV, Hosea TJC, Sweeney SJ, Wang J-B, Johnson SR, Zhang Y-H. (2007) 'Microscopic electroabsorption line shape analysis for Ga(AsSb)/GaAs heterostructures'. JOURNAL OF APPLIED PHYSICS, 101 (3) Article number ARTN 033118
  • 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.

    Abstract

    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 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 μm lasers at high temperature'. Optics InfoBase Conference Papers,
  • 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) Article number ARTN 221105
  • 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) Article number ARTN 191118
  • 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) Article number ARTN 173509
  • 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) Article number ARTN 051104
  • Murdin BN, Adams AR, Sweeney SJ. (2006) 'Band structure and high-pressure measurements'. Springer Series in Optical Sciences, 118, pp. 93-127.

    Abstract

    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.

  • 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.

    Abstract

    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.

  • 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) Article number ARTN 211114
  • 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.

    Abstract

    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.

  • 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.
  • 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.
  • 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.
  • Marko IP, Masse N, Sweeney SJ, Adams AR, Sellers IR, Mowbray DJ, Skolnick MS, Liu HY, Groom KM. (2005) 'Effect of gain saturation and nonradiative recombination on the thermal characteristics of InAs/GaAs 1.3 mu m quantum dot lasers'. 2005 IEEE LEOS Annual Meeting Conference Proceedings (LEOS), Sydney, AUSTRALIA: , pp. 401-402.
  • Hild K, Sweeney SJ, Lock DA, Wright S, Wang JB, Johnson SR, Zhang YH. (2005) 'On the thermal stability of 1.3 mu m GaAsSb/GaAs-based lasers'. 2005 IEEE LEOS Annual Meeting Conference Proceedings (LEOS), Sydney, AUSTRALIA: , pp. 330-331.
  • Masse NF, Marko IP, Sweeney SJ, 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), Sydney, AUSTRALIA: , pp. 603-604.
  • 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.
  • 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, CARDIFF, WALES: 151 (2), pp. 94-97.
  • Sweeney SJ. (2004) 'Novel experimental techniques for semiconductor laser characterisation and optimisation'. PHYSICA SCRIPTA, T114, pp. 152-158.
  • Sweeney SJ, Lyons LJ, Adams AR, Lock DA. (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.
  • Tomic S, O'Reilly EP, Fehse R, Sweeney SJ, Adams AR, Andreev AD, Choulis SA, 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.

    Abstract

    We present a comprehensive theoretical and experimental analysis of 1.3-μm 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.

  • Jin SR, Sweeney SJ, 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.
  • Knowles G, Fehse R, Tomic S, Sweeney SJ, Sale TE, 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.

    Abstract

    We have investigated the temperature and pressure dependence of the threshold current (I) of 1-3 μm 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 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. 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 at 350 K and above is due largely to Auger recombination.

  • 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.
  • 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.
  • 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.
  • O'Reilly EP, Fahy S, Lindsay A, Tomić 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.

    Abstract

    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.

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

    Abstract

    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.

  • 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 μm operation'. Conference Digest - IEEE International Semiconductor Laser Conference, , pp. 43-44.

    Abstract

    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.

  • 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.

    Abstract

    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.

  • Sweeney SJ, Lock D, Adams AR, Lyons LJ. (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.

    Abstract

    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.

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

    Abstract

    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.

  • 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.
  • Knowles G, Sweeney SJ, Sale TE, Adams AR. (2001) 'Self-heating effects in red (665 nm) VCSELs'. IEE PROCEEDINGS-OPTOELECTRONICS, 148 (5-6) Article number PII 10.1049/ip-opt:20010843 , pp. 256-260.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • Sweeney SJ, Adams AR, O'Reilly EP, Silver M, Thijs PJA. (2000) 'Effect of auger generated hot-holes on 1.5-μm InGaAs(P)-based quantum well semiconductor lasers'. Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digest, , pp. 391-392.

    Abstract

    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.

  • 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, MONTEREY, CA: , pp. 15-16.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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 μm and 1.5 μm InGaAs(P) strained-layer lasers and its variation with temperature'. Conference Digest - IEEE International Semiconductor Laser Conference, , pp. 63-64.

    Abstract

    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.

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

    Abstract

    Measurements of the threshold current, I 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, T. 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 T(I)= T holds true even to above room temperature.

  • 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-μm AlGaInAs/InP multiple-quantum-well lasers'. Conference Digest - IEEE International Semiconductor Laser Conference, , pp. 61-62.

    Abstract

    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.

Conference papers

  • Crutchley BG, Marko IP, Adams AR, Sweeney SJ. (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,

    Abstract

    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.

  • Crutchley BG, Marko IP, Adams AR, Sweeney SJ. (2013) 'Investigating the efficiency limitations of GaN-based emitters'. Optics InfoBase Conference Papers,
  • Hild K, Batool Z, Jin SR, Hossain N, Marko IP, Hosea TJC, Lu X, Tiedje T, Sweeney SJ, Ihn T, Rossler C, Kozikov A. (2013) 'Auger Recombination Suppression And Band Alignment In GaAsBi/GaAs Heterostructures'. AMER INST PHYSICS PHYSICS OF SEMICONDUCTORS, Zurich, SWITZERLAND: 31st International Conference on the Physics of Semiconductors (ICPS) 1566, pp. 488-489.
  • Hossain N, Hosea J, Liebich S, Zimprich M, Volz K, Kunert B, Stolz W, Sweeney S, Ihn T, Rossler C, Kozikov A. (2013) 'Band Structure Properties of (BGa)P Semiconductors for Lattice Matched Integration on (001) Silicon'. AMER INST PHYSICS PHYSICS OF SEMICONDUCTORS, Zurich, SWITZERLAND: 31st International Conference on the Physics of Semiconductors (ICPS) 1566, pp. 47-48.
  • Ikyo BA, Marko IP, Hild K, Adams AR, Sweeney SJ, Arafin S, Amann M-C. (2013) 'The effect of hole leakage and auger recombination on the temperature sensitivity of GaInAsSb/GaSb mid-infrared lasers'. Optics InfoBase Conference Papers,
  • Hosea TJC, Chai GMT, Marko IP, Batool Z, Hild K, Jin SR, Hossain N, 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.

    Abstract

    Replacing small amounts of As with Bi in InGaBiAs/InP induces large decreases and increases in the bandgap, E, and spin-orbit splitting, Δ, respectively. The possibility of achieving Δ>E and a reduced temperature (T) dependence for E are significant for suppressing recombination losses and improving performance in mid-infrared photonic devices. We measure E (x, T) and Δ(x, T) in InGa BiAs/InP samples for 0≤x≤0.032 by optical spectroscopy. While we find no clear evidence of a decreased dE /dT (≈0.33±0.07meV/K in all samples) we find Δ>E for x>3.3-4.3%. The predictions of a valence band anti-crossing model agree well with the measurements. © 2012 IEEE.

  • Lever L, Hu Y, Myronov M, Liu X, Owens N, Gardes FY, Marko IP, Sweeney SJ, Ikonić Z, Leadley DR, Reed GT, Kelsall RW. (2011) 'Strain engineering of the electroabsorption response in Ge/SiGe multiple quantum well heterostructures'. IEEE 8th IEEE International Conference on Group IV Photonics, London, UK: Group IV Photonics, pp. 107-108.

    Abstract

    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.

  • Sweeney SJ, Batool Z, Hild K, Jin SR, Hosea TJC. (2011) 'The Potential Role of Bismide Alloys in Future Photonic Devices'. IEEE 13TH INTERNATIONAL CONFERENCE ON TRANSPARENT OPTICAL NETWORKS, Stockholm, Sweden: 13th ICTON

    Abstract

    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.

  • 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'. IEEE 8th IEEE International Conference on Group IV Photonics, London, UK: Group IV Photonics, pp. 148-150.

    Abstract

    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.

  • 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, Orchard, Singapore: PGC 2010

    Abstract

    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.

  • Ongrai O, Pearce JV, Machin G, Sweeney SJ. (2010) 'Comparative Study of Pt/Pd and Pt-Rh/Pt Thermocouples'. SPRINGER/PLENUM PUBLISHERS INTERNATIONAL JOURNAL OF THERMOPHYSICS, Portoroz, SLOVENIA: 1st TEMPMEKO and ISHM Joint International Symposium on Temperature, Humidity, Moisture, and Thermal Measurements 31 (8-9), pp. 1506-1516.
  • Sayid SA, Marko IP, Sweeney SJ, Poole P. (2010) 'Temperature sensitivity of 1.55μm (100) InAs/InP-based quantum dot lasers'. IEEE Proceedings of 22nd International Conference on Indium Phosphide and Related Materials, Kagawa, Japan: 22nd IPRM, pp. 23-24.

    Abstract

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

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

    Abstract

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

  • 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, Kyoto, Japan: 22nd IEEE ISLC, pp. 109-110.
  • 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, Orchard, Singapore: PGC 2010

    Abstract

    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.

  • Crutchley BG, Marko IP, Adams AR, Sweeney SJ. (2010) 'Efficiency limitations of green InGaN LEDs and laser diodes'. 22nd IEEE International Semiconductor Laser Conference, Kyoto, Japan: ISLC 2010, pp. 27-28.
  • 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'. IEEE 23rd Annual Meeting of the IEEE Photonics Society, Denver, USA: Photonics 2010, pp. 59-60.

    Abstract

    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.

  • Sweeney SJ. (2010) 'Bismide-alloys for higher efficiency infrared semiconductor lasers'. IEEE 22nd IEEE International Semiconductor Laser Conference, Kyoto, Japan: ISLC 2010, pp. 111-112.

    Abstract

    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.

  • 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'. SPIE Proceedings of SPIE - Posters Session, Brussels, Belgium: Optical Sensing and Detection 7726

    Abstract

    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.

  • 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, Kyoto, Japan: 22nd IEEE ISLC, pp. 143-144.

    Abstract

    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.

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

    Abstract

    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.

  • 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'. IEEE 23rd Annual Meeting of the IEEE Photonics Society, Denver, USA: Photonics 2010, pp. 65-66.

    Abstract

    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.

  • Hossain N, Jin SR, Sweeney SJ, Yu S-Q, Johnson SR, Ding D, Zhang Y-H, Belyanin AA, Smowton PM. (2010) 'Improved Performance of GaAsSb/GaAs SQW Lasers'. SPIE-INT SOC OPTICAL ENGINEERING NOVEL IN-PLANE SEMICONDUCTOR LASERS IX, San Francisco, CA: Conference on Novel In - Plane Semiconductor Lasers IX 7616
  • 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'. Kagawa, Japan: IPRM 2010, pp. 187-190.

    Abstract

    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.

  • 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 4.1μm at room temperature'. IEEE 22nd IEEE International Semi-conductor Laser Conference, Kyoto, Japan: ISLC 2010, pp. 41-42.

    Abstract

    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.

  • 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'. INST ENGINEERING TECHNOLOGY-IET IET OPTOELECTRONICS, Cardiff, WALES: Semiconductor and Integrated Optoelectronics Conference (SIOE 2009) 3 (6), pp. 305-309.
  • 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-μm GaSb buried tunnel junction VCSELs'. Proceedings of European Conference on Lasers and Electro-Optics 2009 and the European Quantum Electronics Conference, Munich, Germany: CLEO Europe - EQEC 2009

    Abstract

    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.

  • 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'. WILEY-BLACKWELL PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, Wroclaw Univ Technol, Wroclaw, POLAND: 3rd International Workshop on Modulation Spectroscopy of Semiconductor Structures 206 (5), pp. 796-802.
  • 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'. WILEY-V C H VERLAG GMBH PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, Fortaleza, BRAZIL: 13th International Conference on High Pressure Semiconductor Physics (HPSP-13) 246 (3), pp. 527-531.
  • 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'. WILEY-V C H VERLAG GMBH PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, Fortaleza, BRAZIL: 13th International Conference on High Pressure Semiconductor Physics (HPSP-13) 246 (3), pp. 512-515.
  • Adams AR, Marko IP, Sweeney SJ, Teissier R, Baranov AN, Tomić S. (2009) 'The effect of hydrostatic pressure on the operation of quantum cascade lasers'. SPIE Proceedings of SPIE - Quantum Cascade Lasers and Applications I, San Jose, USA: Quantum Sensing and Nanophotonic Devices VI 7222

    Abstract

    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.

  • 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-μm GaSb buried tunnel junction VCSELs'. Optics InfoBase Conference Papers,
  • 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 IEEE Proceedings of LEOS Annual Meeting Conference, Belek-Antalya, Turkey: LEOS '09, pp. 233-234.

    Abstract

    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.

  • 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'. IEEE 2008 IEEE 21ST INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE, Sorrento, ITALY: IEEE 21st International Semiconductor Laser Conference, pp. 83-84.
  • 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'. IEEE 2008 IEEE 21ST INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE, Sorrento, ITALY: IEEE 21st International Semiconductor Laser Conference, pp. 47-48.
  • 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, Versailles, France: IPRM 2008

    Abstract

    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.

  • 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'. IEEE Proccedings of 20th International Conference on Indium Phosphide and Related Materials, Versailles, France: IPRM 2008

    Abstract

    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.

  • Chamings J, Adams AR, Sweeney SJ, Kunert B, Volz K, Stolz W. (2008) 'Thermal properties of Silicon compatible GaNAsP SQW lasers'. IEEE 2008 IEEE 21ST INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE, Sorrento, ITALY: IEEE 21st International Semiconductor Laser Conference, pp. 61-62.
  • 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, Santa Barbara, USA: 66th DRC, pp. 309-310.

    Abstract

    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.

  • 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 1.3μm quantum dot lasers'. IEEE IEEE Proceedings of 21st International Semiconductor Laser Conference, Sorento, Italy: 21st ISLC 2008, pp. 117-118.

    Abstract

    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.

  • 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, Santa Barbara, USA: 66th DRC, pp. 299-300.

    Abstract

    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.

  • Coote J, Reddy S, Sweeney SJ. (2007) 'Optimisation of distributed feedback laser biosensors'. INST ENGINEERING TECHNOLOGY-IET IET OPTOELECTRONICS, Cardiff, WALES: 21st Conference on Semiconductor Integrated Optoelectronics (SIOE) 1 (6), pp. 266-271.
  • 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'. WILEY-V C H VERLAG GMBH PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, Barcelona, SPAIN: 12th International Conference on High Pressure Semiconductor Physics (HPSP-12) 244 (1), pp. 82-86.
  • 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'. WILEY-V C H VERLAG GMBH PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, Barcelona, SPAIN: 12th International Conference on High Pressure Semiconductor Physics (HPSP-12) 244 (1), pp. 203-207.
  • Marko IP, Masse NF, Sweeney SJ, Adams AR, Hatori N, Sugawara M, Jantsch W, Schaffler F. (2007) 'Recombination, transport and loss mechanisms in p-doped InAs/GaAs quantum dots'. AMER INST PHYSICS Physics of Semiconductors, Pts A and B, Vienna, AUSTRIA: 28th International Conference on the Physics of Semiconductors (ICPS-28) 893, pp. 837-838.
  • 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'. WILEY-V C H VERLAG GMBH PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, Barcelona, SPAIN: 12th International Conference on High Pressure Semiconductor Physics (HPSP-12) 244 (1), pp. 208-212.
  • Hild K, Sweeney SJ, Jin SR, Healy SB, O'Reilly EP, Johnson SR, Wang J-B, Zhang Y-H. (2007) 'Band alignment and carrier recombination in GaAsSb/GaAs quantum wells'. AIP Conference Proceedings, 893, pp. 1431-1432.

    Abstract

    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 ∼30%, the band alignment is slightly type II. From studies on lasers based upon this material we show that at the high carrier densities required to achieve threshold, at room temperature, the devices are dominated by carrier leakage and non-radiative Auger recombination. © 2007 American Institute of 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'. WILEY-V C H VERLAG GMBH PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, Barcelona, SPAIN: 12th International Conference on High Pressure Semiconductor Physics (HPSP-12) 244 (1), pp. 224-228.
  • 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'. WILEY-V C H VERLAG GMBH PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, Barcelona, SPAIN: 12th International Conference on High Pressure Semiconductor Physics (HPSP-12) 244 (1), pp. 197-202.
  • 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 μm lasers at high temperature'. Conference on Lasers and Electro-Optics Europe - Technical Digest,
  • Massé NF, Sweeney SJ, Marko IP, Andreev AD, Adams AR, Hatori N, Sugawara M. (2006) 'Intrinsic limitations of p-doped and undoped 1.3 μm InAs/GaAs quantum dot lasers'. Conference Digest - IEEE International Semiconductor Laser Conference, , pp. 143-144.
  • Adams AR, Sweeney SJ. (2006) 'The physics controlling the sensitivity of semiconductor lasers to high temperatures'. OPTICAL SOC AMERICA 2006 OPTICAL FIBER COMMUNICATION CONFERENCE/NATIONAL FIBER OPTIC ENGINEERS CONFERENCE, VOLS 1-6, Anaheim, CA: Conference on Optical Fiber Communications/National Fiber Optic Engineers Conference, pp. 1631-1633.
  • Marko IP, Adams AR, Sweeney SJ, 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-INST ELECTRICAL ELECTRONICS ENGINEERS INC IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, Matsue, JAPAN: 19th IEEE International Semiconductor Laser Conference 11 (5), pp. 1041-1047.
  • Blume G, Hosea TJC, Sweeney SJ. (2005) 'A study of the low-energy interference oscillations in photoreflectance of GaAsSb/GaAs quantum well structures'. WILEY-V C H VERLAG GMBH PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, Wroclaw, POLAND: International Workshop on Modulation Spectroscopy of Semiconductor Structures 202 (7), pp. 1244-1254.
  • Marko IP, Andreev AD, Sweeney SJ, Adams AR, Krebs R, Deubert S, Reithmaier JP, Forchel A, Menendez J, VanDeWalle CG. (2005) 'The influence of auger processes on recombination in long-wavelength InAs/GaAs quantum dots'. AMER INST PHYSICS Physics of Semiconductors, Pts A and B, Flagstaff, AZ: 27th International Conference on the Physics of Semiconductors (ICPS-27) 772, pp. 681-682.
  • Sweeney SJ, Lock DA, Adams AR, Menendez J, VanDeWalle CG. (2005) 'Carrier recombination in InGaAs(P) quantum well laser structures: Band gap and temperature dependence'. AMER INST PHYSICS Physics of Semiconductors, Pts A and B, Flagstaff, AZ: 27th International Conference on the Physics of Semiconductors (ICPS-27) 772, pp. 1545-1546.
  • Lock D, Sweeney SJ, Adams AR. (2004) 'Pressure induced wavelength dependence of catastrophic optical damage in 980 nm semiconductor diode lasers'. WILEY-V C H VERLAG GMBH PHYSICA STATUS SOLIDI B-BASIC RESEARCH, Berkeley, CA: 11th International Conference on High-Pressure Semiconductor Physics (HPSP-11) 241 (14), pp. 3416-3419.
  • 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'. WILEY-V C H VERLAG GMBH PHYSICA STATUS SOLIDI B-BASIC RESEARCH, Berkeley, CA: 11th International Conference on High-Pressure Semiconductor Physics (HPSP-11) 241 (14), pp. 3405-3409.
  • 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'. WILEY-V C H VERLAG GMBH PHYSICA STATUS SOLIDI B-BASIC RESEARCH, Berkeley, CA: 11th International Conference on High-Pressure Semiconductor Physics (HPSP-11) 241 (14), pp. 3427-3431.
  • 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'. WILEY-V C H VERLAG GMBH PHYSICA STATUS SOLIDI B-BASIC RESEARCH, Berkeley, CA: 11th International Conference on High-Pressure Semiconductor Physics (HPSP-11) 241 (14), pp. 3399-3404.
  • 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'. WILEY-V C H VERLAG GMBH PHYSICA STATUS SOLIDI B-BASIC RESEARCH, Berkeley, CA: 11th International Conference on High-Pressure Semiconductor Physics (HPSP-11) 241 (14), pp. 3391-3398.
  • 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-INST ELEC ENG IEE PROCEEDINGS-OPTOELECTRONICS, Strasbourg, FRANCE: Symposium on Dilute Nitride and Related Mismatched Semiconductor Alloys held at the 2004 Spring Meeting of the EMRS 151 (5), pp. 447-451.
  • Marko IP, Adams AR, Sweeney SJ, Sellers IR, Mowbray DJ, Skolnick MS, Liu HY, Groom KM, Messe K. (2004) 'Recombination and loss mechanisms in low-threshold InAs/GaAs 1.3 mu m quantum dot lasers'. IEEE 2004 IEEE 19TH INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE, CONFERENCE DIGEST, Matsue, JAPAN: 19th IEEE International Semiconductor Laser Conference, pp. 57-58.
  • Sweeney SJ, McConville D, Jin SR, Ahmad CN, Masse NF, Bouyssou RX, Adams AR, Hanke C. (2004) 'Temperature and wavelength dependence of recombination processes in 1.5 mu m InGaAlAs/InP-based lasers'. IEEE 2004 International Conference on Indium Phosphide and Related Materials, Conference Proceedings, Kagoshima, JAPAN: 16th International Conference on Indium Phosphide and Related Materials, pp. 738-741.
  • Fehse R, Sweeney SJ, Adams AR, McConville D, Riechert H, Geelhaar L. (2004) 'Influence of growth temperature on defect density in 1.3 mu m GaInNAs-based lasers'. IEEE 2004 IEEE 19TH INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE, CONFERENCE DIGEST, Matsue, JAPAN: 19th IEEE International Semiconductor Laser Conference, pp. 85-86.
  • Marko IP, Adams AR, Sweeney SJ, Jin SR, Murdin BN, Schwertberger R, Somers A, Reithmaier JP, Forchel A, Messe K. (2004) 'Experimental investigations into the thermal properties of 1.5-1.8-mu m InAs/InP quantum dash lasers'. IEEE 2004 IEEE 19TH INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE, CONFERENCE DIGEST, Matsue, JAPAN: 19th IEEE International Semiconductor Laser Conference, pp. 61-62.
  • 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'. PERGAMON-ELSEVIER SCIENCE LTD SOLID-STATE ELECTRONICS, STRASBOURG, FRANCE: Spring Meeting of the European-Materials-Research-Society (E-MRS) 47 (3), pp. 501-506.
  • 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'. WILEY-V C H VERLAG GMBH PHYSICA STATUS SOLIDI B-BASIC RESEARCH, UNIV SURREY, GUILDFORD, ENGLAND: 10th International Conference on High Pressures in Semiconductor Physics (HPSP-X) 235 (2), pp. 491-495.
  • 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'. WILEY-V C H VERLAG GMBH PHYSICA STATUS SOLIDI B-BASIC RESEARCH, UNIV SURREY, GUILDFORD, ENGLAND: 10th International Conference on High Pressures in Semiconductor Physics (HPSP-X) 235 (2), pp. 547-551.
  • Lock D, Sweeney SJ, Adams AR, Robbins DJ. (2003) 'Auger recombination in InGaAs/AlGaAs-based MQW semiconductor lasers emitting at 980 nm'. WILEY-V C H VERLAG GMBH PHYSICA STATUS SOLIDI B-BASIC RESEARCH, UNIV SURREY, GUILDFORD, ENGLAND: 10th International Conference on High Pressures in Semiconductor Physics (HPSP-X) 235 (2), pp. 542-546.
  • 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'. WILEY-V C H VERLAG GMBH PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, UNIV SURREY, GUILDFORD, ENGLAND: 10th International Conference on High Pressures in Semiconductor Physics (HPSP-X) 235 (2), pp. 480-485.
  • 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'. WILEY-V C H VERLAG GMBH PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, UNIV SURREY, GUILDFORD, ENGLAND: 10th International Conference on High Pressures in Semiconductor Physics (HPSP-X) 235 (2), pp. 474-479.
  • Jin SR, Sweeney SJ, Tomic S, Adams AR, Riechert H. (2003) 'Quantifying pressure-dependent recombination currents in GaInNAs lasers using spontaneous emission measurements'. WILEY-V C H VERLAG GMBH PHYSICA STATUS SOLIDI B-BASIC RESEARCH, UNIV SURREY, GUILDFORD, ENGLAND: 10th International Conference on High Pressures in Semiconductor Physics (HPSP-X) 235 (2), pp. 486-490.
  • Sweeney SJ, Thijs PJA. (2003) 'Origin of the high temperature performance degradation of 1.5 mu m InGaAs(P)/InP quantum well lasers'. IEEE 2003 IEEE LEOS ANNUAL MEETING CONFERENCE PROCEEDINGS, VOLS 1 AND 2, TUCSON, AZ: 16th Annual Meeting of the IEEE Lasers and Electro-Optics Society, pp. 977-978.
  • Lock D, Sweeney SJ, Adams AR. (2003) 'Wavelength dependence of catastrophic optical damage threshold in 980nm semiconductor diode lasers'. IEEE 2003 IEEE LEOS ANNUAL MEETING CONFERENCE PROCEEDINGS, VOLS 1 AND 2, TUCSON, AZ: 16th Annual Meeting of the IEEE Lasers and Electro-Optics Society, pp. 421-422.
  • Lock D, Sweeney SJ, Adams AR. (2003) 'Fundamental limitations of high power 980nm InGaAs/GaAs pump lasers'. IEEE 2003 IEEE LEOS ANNUAL MEETING CONFERENCE PROCEEDINGS, VOLS 1 AND 2, TUCSON, AZ: 16th Annual Meeting of the IEEE Lasers and Electro-Optics Society, pp. 427-428.
  • Sweeney SJ, 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'. IEEE 2003 IEEE LEOS ANNUAL MEETING CONFERENCE PROCEEDINGS, VOLS 1 AND 2, TUCSON, AZ: 16th Annual Meeting of the IEEE Lasers and Electro-Optics Society, pp. 39-40.
  • Adams AR, Fehse R, Tomic S, O'Reilly EP, Andreev A, Knowles G, Sale TE, Sweeney SJ, Steinle G, Ramakrishnan A, Riechert H, ChangHasnain CJ, Xia YX, Iga K. (2002) 'Characterisation of 1.3pm wavelength GaInNAs/GaAs edge-emitting and vertical-cavity surface-emitting lasers using low-temperature and high-pressure'. SPIE-INT SOC OPTICAL ENGINEERING APOC 2002: ASIA-PACIFIC OPTICAL AND WIRELESS COMMUNICATIONS; MATERIALS AND DEVICES FOR OPTICAL AND WIRELESS COMMUNICATIONS, SHANGHAI, PEOPLES R CHINA: Conference on Asia-Pacific Optical and Wireless Communication (APOC 2002) 4905, pp. 183-197.
  • 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-INST ELEC ENG IEE PROCEEDINGS-OPTOELECTRONICS, CARDIFF, WALES: Conference on Semiconductor Optoelectronics 148 (1), pp. 55-59.
  • 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'. IEEE LEOS 2001: 14TH ANNUAL MEETING OF THE IEEE LASERS & ELECTRO-OPTICS SOCIETY, VOLS 1 AND 2, PROCEEDINGS, SAN DIEGO, CA: 14th Annual Meeting of the IEEE Lasers-and-Electro-Optics-Society, pp. 330-331.
  • 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'. GORDON BREACH SCI PUBL LTD HIGH PRESSURE RESEARCH, UNIV MONTPELLIER, MONTPELLIER, FRANCE: XXXVIIth Meeting of the European-High-Pressure-Research-Group (EHPRG) 18 (1-6), pp. 49-55.
  • 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'. WILEY-V C H VERLAG GMBH PHYSICA STATUS SOLIDI B-BASIC RESEARCH, THESSALONIKI, GREECE: 8th International Conference on High Pressure Semiconductor Physics (HPSP-VIII) 211 (1), pp. 513-518.
  • 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'. WILEY-V C H VERLAG GMBH PHYSICA STATUS SOLIDI B-BASIC RESEARCH, THESSALONIKI, GREECE: 8th International Conference on High Pressure Semiconductor Physics (HPSP-VIII) 211 (1), pp. 525-531.
  • 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'. AKADEMIE VERLAG GMBH PHYSICA STATUS SOLIDI B-BASIC RESEARCH, SCHWABISCH GMUND, GERMANY: 7th International Conference on High Pressure Semiconductor Physics (HPSP-VII) 198 (1), pp. 381-388.

Patents

  • Sweeney S. (2009) Optoelectronic Devices. Article number GB0911134.5

Teaching

Current:

Level 2 Solid State Physics

Level 2 Laboratories
 

Past:

Level 0 Foundation Year Tutorials
Level 1 Principles of Physics (1PP)

Level 1 Electronics (1EL)

Level 1 Physics Laboratories (1LAB)
Level 3 Physics in Education (3PIE) [assessor]
Level M Photonics and Nanotechnology (3PNT)

Level D LabView
 

Departmental Duties

  • Head of Photonics group (2010-)
  • Departmental Management group (2010-)
  • Departmental Policy & Strategy group (2008-)
  • Departmental & Faculty Research Committee (2010-)
  • Chair, Physics Publicity & Marketing group (2010-13)
  • Chair of Physics Department Board of Studies (2008-10)
  • Chair of Physics Department BoS sub-committee (2008-10)
  • MPhys/BSc Physics Programme Coordinator (2008-10)
  • Physics with Foundation Year Co-ordinator (2003-2006)
  • Physics Schools Liaison Officer (2004-2008)
  • Physics Marketing group (2006-2008)
  • Physics MPhys research placements co-ordinator (2006-2010)
  • ATI Postgraduate Admissions Tutor (2002-2008)
  • FEPS PG Research committee (2002-2008)

Affiliations

  • Fellow of the Institute of Physics, Chartered Physicist and a Senior Member of the Institute of Electrical and Electronic Engineers.
  • Editorial Boards of the Journal of Quantum Electronics and the Journal of Materials Science: Materials in Electronics. 
  • Proposal Reviewer/advisor: EPSRC College Member, EU Photonics 21 Member, US Dept of Energy, Singapore A* Research Agency, Lithuanian Research Council, Humbolt Foundation, Austrian research agency, EU-Framework projects and NSF (USA).

Research Grants

Stephen currently has ~£3M of research funding from sources including EPSRC, EU, TSB and commercial organisations.

Page Owner: phs1ss
Page Created: Monday 10 August 2009 13:24:44 by lb0014
Last Modified: Tuesday 15 July 2014 11:55:50 by pg0016
Expiry Date: Wednesday 10 November 2010 13:23:47
Assembly date: Sat Dec 20 00:25:15 GMT 2014
Content ID: 11724
Revision: 14
Community: 1256