Dr. John S. Roberts Profile

Dr. John S. Roberts

at Univ of Sheffield

SPIE Involvement:

Author

Publications (20)

Proceedings Article | 26 February 2010 Paper

Higher limiting efficiencies for nanostructured solar cells

Jessica G. Adams, Warren Elder, Geoff Hill, John Roberts, Keith W. Barnham, Nicholas Ekins-Daukes

Proc. SPIE. 7597, Physics and Simulation of Optoelectronic Devices XVIII

KEYWORDS: Semiconductors, Mirrors, Quantum wells, Nanostructuring, Solar cells, Gallium arsenide, Indium, Quantum efficiency, Reflectivity, Absorption

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Proceedings Article | 12 February 2010 Paper

A platform for GaAs opto-electronic integrated circuits based on GaAs/AlGaAs regrowth upon patterned InGaP

Kristian Groom, Benjamin Stevens, Punima Greenwood, David Childs, John Roberts, Matthew Lomas, Maxime Hugues, Hifsa Shahid, Richard Hogg

Proc. SPIE. 7616, Novel In-Plane Semiconductor Lasers IX

KEYWORDS: Waveguides, Cladding, Etching, Gallium arsenide, Reflectivity, Semiconductor lasers, Integrated circuits, Photonic integrated circuits, Indium gallium phosphide

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Proceedings Article | 25 October 2006 Paper

Probing the electronic and optical properties of quantum cascade lasers under operating conditions

D. Revin, M. Soulby, J. Cockburn, A. Krysa, J. Roberts, R. Airey, R. Nelander, M. Pereira, A. Wacker

Proc. SPIE. 6386, Optical Methods in the Life Sciences

KEYWORDS: Continuous wave operation, Waveguides, Polarization, Spectroscopy, Electrons, Quantum cascade lasers, Transmittance, Laser damage threshold, Temperature metrology, Absorption

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Proceedings Article | 18 November 2005 Paper

Single mode quantum cascade lasers

M. Austerer, C. Pflügl, S. Golka, S. Schartner, W. Schrenk, R. Green, L. Wilson, J. Cockburn, A. Krysa, J. Roberts, G. Strasser

Proc. SPIE. 6010, Infrared to Terahertz Technologies for Health and the Environment

KEYWORDS: Continuous wave operation, Waveguides, Cladding, Etching, Gallium arsenide, Silicon, Quantum cascade lasers, Semiconductor lasers, Pulsed laser operation, Temperature metrology

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Proceedings Article | 13 April 2005 Paper

Temperature dependence of the threshold electric field in a hot electron VCSEL

Ali Serpenguzel, Naci Balkan, Ayse Erol, M. Cetin Arikan, John Roberts

Proc. SPIE. 5725, Ultrafast Phenomena in Semiconductors and Nanostructure Materials IX

KEYWORDS: Electronics, Quantum wells, Gallium arsenide, Reflectivity, Physics, Electroluminescence, Aluminum, Vertical cavity surface emitting lasers, Gallium, Temperature metrology

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Proceedings Article | 22 October 2004 Paper

High-performance quantum cascade lasers grown by metal-organic vapor phase epitaxy

Luke Wilson, Richard Green, Andrey Krysa, John Roberts, Wing Ng, Dmitry Revin, Christian Pflugl, Werner Schrenk, Gottfried Strasser, John Cockburn

Proc. SPIE. 5564, Infrared Detector Materials and Devices

KEYWORDS: Indium gallium arsenide, Switching, Waveguides, Silicon, Quantum cascade lasers, Doping, Semiconducting wafers, Superlattices, Vapor phase epitaxy, Temperature metrology

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Proceedings Article | 18 October 2004 Paper

Optoelectronic integrated tweezers

Simon McGreehin, Liam O'Faolin, John Roberts, Thomas Krauss, Kishan Dholakia

Proc. SPIE. 5514, Optical Trapping and Optical Micromanipulation

KEYWORDS: Optical trapping, Optical spheres, Etching, Polymers, Particles, Semiconductor lasers, Optoelectronics, Optical tweezers, Optical alignment, Optical manipulation

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Proceedings Article | 11 June 2003 Paper

Influence of temperature and free carries on four-wave mixing in semiconductor microcavities

M. Makhonin, D. Krizhanovskii, A. Dremin, A. Tartakovskii, V. Kulakovskii, N. Gippius, Maurice Skolnick, John Roberts

Proc. SPIE. 5023, 10th International Symposium on Nanostructures: Physics and Technology

KEYWORDS: Semiconductors, Scattering, Phonons, Sapphire lasers, Excitons, Polaritons, Four wave mixing, Optical microcavities, Temperature metrology, Absorption

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In semiconductor microcavities (MCs) with embedded quantum wells (QW) a strong two-dimensional (2D) confinement of the light in the growth direction leads to an enhanced exciton-photon interaction, which results in the formation of mixed exciton-photon states described in terms of quasi 2D-polaritons. The density of these states is strongly reduced compared to exciton one, due to a very small in-plane mass. As a result, one can hope that the high filling of the polariton states near the polariton band bottom can be achieved at relatively small total density without destroying the strong coupling regime. However such a filling never was reached at low excitation density range where the polariton relaxation to the polariton branch bottom is determined by the emission of acoustic phonons. The reason is in the fact that the polariton lifetime is comparable with phonon scattering time. As a result, the energy distribution of polaritons clearly demonstrates 'bottleneck effect' both under the above band gap excitation and the resonant excitation below free exciton level. However the high occupation of polariton states near the band bottom is relatively easy reached under conditions of a strong resonant excitation into the lower polariton (LP) branch at particular wavenumbers close to the inflection point of the LP dispersion. It is explained as the result of stimulated hyper-Raman scattering (or four-wave mixing) of pumped polaritons with (E_p, k_p) to states with the energy and momentum [E₁, k₁ approximately 0] and [E₂ = 2E_p - E₁, k₂ = 2k_p], which referred to as the 'signal' and 'idler,' respectively. Here we investigate the influence of a temperature and an additional above band gap excitation on the stimulated scattering in MCs. A GaAs/AlAs MC containing 6 InGaAs quantum wells in the active layer (Rabi splitting Ω of 6 - 7 meV) has been investigated in a wide range of detunings between free exciton level and bottom of the photonic mode from δ = 0 to -3 meV. The resonance excitation into an LP branch was carried out with a tunable Ti-sapphire laser. The HeNe laser was used for the additional above GaAs band gap excitation. The sample was mounted in a helium thermostat with the temperature control at T = 5 - 30 K.

Proceedings Article | 9 July 2001 Paper

Nonlinear dynamics in a graded quantum well placed in a GaAlAs p-n junction

Naci Balkan, Huseyin Sari, Andreas Schroeder, Yuksel Ergun, Ismail Sokmen, John Roberts

Proc. SPIE. 4283, Physics and Simulation of Optoelectronic Devices IX

KEYWORDS: Optical fibers, Quantum wells, Sensors, Electrons, Gallium arsenide, Physics, Wavelength division multiplexing, Electroluminescence, Lanthanum, Absorption

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Proceedings Article | 18 April 2000 Paper

Residual oxygen contamination of InAlGaAs SQW high-power laser diodes

John Roberts, Lesley Smith, Peter Tihanyi

Proc. SPIE. 3947, In-Plane Semiconductor Lasers IV

KEYWORDS: Quantum wells, Contamination, Cladding, High power lasers, Indium, Oxygen, Diodes, Aluminum, Semiconducting wafers, Gallium

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Proceedings Article | 6 August 1999 Paper

Hot-electron VCSEL

Naci Balkan, Ismail Sokmen, Angela O'Brien-Davies, Richard Potter, Carl Hepburn, Adrian Boland-Thoms, Michael Adams, John Roberts

Proc. SPIE. 3625, Physics and Simulation of Optoelectronic Devices VII

KEYWORDS: Semiconductors, Quantum wells, Gallium arsenide, Reflectivity, Physics, Electroluminescence, Measurement devices, Vertical cavity surface emitting lasers, Semiconducting wafers, Electron transport

Proceedings Article | 7 July 1998 Paper

Theoretical and experimental analysis of the spontaneous emission and threshold current of edge-emitting Bragg microcavity laser structures

Graham Berry, Gareth Lewis, Huw Summers, Peter Blood, John Roberts

Proc. SPIE. 3283, Physics and Simulation of Optoelectronic Devices VI

KEYWORDS: Refractive index, Mirrors, Quantum wells, Waveguides, Polarization, Gallium arsenide, Reflectivity, Transition metals, Laser damage threshold, Optical microcavities

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Proceedings Article | 7 July 1998 Paper

Operation of a novel hot-electron vertical-cavity surface-emitting laser

Naci Balkan, Angela O'Brien-Davies, A. Thoms, Richard Potter, Nigel Poolton, Michael Adams, J. Masum, Alpan Bek, Ali Serpenguzel, Atilla Aydinli, John Roberts

Proc. SPIE. 3283, Physics and Simulation of Optoelectronic Devices VI

KEYWORDS: Semiconductors, Quantum wells, Lasers, Gallium arsenide, Diffusion, Reflectivity, Physics, Electroluminescence, Vertical cavity surface emitting lasers, Electron transport

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SPIE Journal Paper | 1 April 1998

Photonic microstructures as laser mirrors

Thomas Krauss, Oskar Painter, Axel Scherer, John Roberts, Richard De La Rue

OE Vol. 37 Issue 04

KEYWORDS: Mirrors, Reflectivity, Photonic microstructures, Laser damage threshold, Waveguides, Semiconductor lasers, Etching, Quantum efficiency, Photonic crystals, Electrical engineering

Proceedings Article | 2 May 1997 Paper

AlxGayIn1-x-yAs/AlGaAs quantum well lasers at 670 to 750 nm

Peter Smowton, Peter Blood, Paul Mogensen, John Roberts

Proc. SPIE. 3001, In-Plane Semiconductor Lasers: from Ultraviolet to Midinfrared

KEYWORDS: Refractive index, Quantum wells, Waveguides, Cladding, Indium, Aluminum, Laser damage threshold, Gallium, Indium gallium phosphide, Temperature metrology

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Proceedings Article | 1 May 1997 Paper

VCSELs for 640- to 1100-nm emission

Terry Sale, John Roberts, John David, R. Grey, Peter Robson

Proc. SPIE. 3004, Fabrication, Testing, and Reliability of Semiconductor Lasers II

KEYWORDS: Reflectors, Mirrors, Quantum wells, Gallium arsenide, Silicon, Resistance, Reflectivity, Aluminum, Vertical cavity surface emitting lasers, Metalorganic chemical vapor deposition

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Proceedings Article | 4 April 1997 Paper

Temperature effects in VCSELs

Terry Sale, John Roberts, John David, R. Grey, Jon Woodhead, Peter Robson

Proc. SPIE. 3003, Vertical-Cavity Surface-Emitting Lasers

KEYWORDS: Oxides, Mirrors, Quantum wells, Data modeling, Resistance, Reflectivity, Thermal effects, Vertical cavity surface emitting lasers, Thermal modeling, Instrument modeling

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Proceedings Article | 19 April 1996 Paper

Tuning of the exciton-photon coupling in semiconductor quantum microcavities by external electric and magnetic fields

T. Fisher, Maurice Skolnick, A. Afshar, D. Whittaker, P. Kinsler, John Roberts, Geoff Hill, M. Pate

Proc. SPIE. 2694, Quantum Well and Superlattice Physics VI

KEYWORDS: Semiconductors, Quantum wells, Oscillators, Photons, Reflectivity, Magnetism, Solids, Excitons, Polaritons, Optical microcavities

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Proceedings Article | 3 September 1992 Paper

Microresonator modulators: design, fabrication, and fine tuning the performance

Gareth Parry, Marco Ghisoni, P. Zouganeli, R. Mottahedeh, A. Rivers, M. Pate, Geoff Hill, John Roberts, Chris Button

Proc. SPIE. 1675, Quantum Well and Superlattice Physics IV

KEYWORDS: Reflectors, Fabry–Perot interferometers, Microresonators, Quantum wells, Interfaces, Reflectivity, Modulators, Aluminum, Semiconducting wafers, Absorption

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