Current Research Interests

Calculation of optical and electronic properties of semiconductors

At the atomic level we are able to determine the electronic band structure of materials using a wide variety of techniques including tight binding, pseudopotential, k.p methods etc. These techniques can be employed on multi-dimensional structures from atomic cluster quantum dots through to bulk semiconductors.

Using the information on the electronic structure of the semiconductor material we are then able to calculate the various optical recombination rates allowing us to describe the operation of optical amplifiers, semiconductor lasers and light emitting diodes. These calculations include many body effects such as Coulomb enhancement of the optical recombination, carrier dephasing and band gap renormalisation. We also model the effects of optical wave-guiding in these devices.

Semiconductor device modelling

To compliment these electronic and optical property calculations we also model semiconductor devices using self consistent Schodinger and Poisson solvers which include electronic drift, diffusion and recombination. Again these solvers can be applied to all quantum structures from quantum dots, quantum wires to bulk semiconductors. We are also interested in the dynamic properties of optoelectronic devices using rate equation models with realistic calculations of electron scattering and current leakage paths. These calculations allow us to model the static and dynamic operating characteristics of a wide variety of electronic and optoelectronic devices.

Simulation of blood clotting

In collaboration with Professor Rhodri Williams (hyper link to) we are developing models to simulate the formation of blood clots in order to determine their mechanical properties and fractal dimensions in order to compare with experimental measurements undertaken at the MNC.

Colloidal quantum dots

We are developing models to calculate the optical properties of colloidal quantum dots starting with tight binding calculations of the electronic band structure allowing the determination of the radiative and non radiative lifetime of the excitons in the dots. To compliment this we also use Monte Carlo methods to investigate Fluorescent Resonant Energy Transfer (FRET) of colloidal dot ensembles to assess their possible use in medical applications.

Flow Cytometry

In collaboration with Dr. Huw Summers, Dr. Rachel Errington and Professor Paul Smith at Cardiff University we are developing Monte Carlo models to monitor the split of quantum dot markers in daughter cells after cell mitosis in flow cytometry experiments. These results can be used to assess the mechanical mechanisms for cell division and to understand the dynamics of cell mitosis.

Selected Publications

2007

• “Calculation of quantum dot blinking using the Gillespie Monte Carlo algorithm”
  M. R. Brown, P. Rees, S. P. Wilks, M. Holton and P. Dunstan, H. D.Summers and Ee Z. Chong
  accepted for publication in IET Proceedings Optoelectronics
• “The Effect of Interface Roughness on Multi-Layer Hetero-Structures”
  M. R. Brown, P. Rees, and S. P. Wilks and A. Hughes
  accepted for publication in J. Appl. Phys.
• “The Influence of the Gain—Carrier Density Characteristic on Q-Switching in Quantum-Dot Lasers”
  H. D. Summers, P. Rees, D. R. Matthews, G. T. Edwards, M. R. Brown, M. Cundin and J. Dominguez
  to appear IEEE J. of Selected Topics in Quant. Electron. Vol. 13, No. 5, 2007.
• “Direct real-time observation of diffusion in operating semiconductor lasers using scanning tunneling microscopy”
  R. J. Cobley, K. S. Teng, M. R. Brown, S. P. Wilks and P. Rees
  to appear Appl. Phys. Lett. Vol. 91, No. 8, 2007
• “Computational Simulation of Optical Tracking of Cell Populations using Quantum Dot Fluorophores”
  M. R. Brown , P. Rees, S. Wilks, H. D. Summers, R. J. Errington, K. L. Njoh, S. C. Chappell, P. J. Smith and J. F. Leary
  to be published in Lecture Notes in Computer Science, Computation Methods for Systems Biology.
• “Derivation of a Modified Fermi-Dirac Distribution for Quantum Dot Ensembles under Non-thermal Conditions”
  H.D. Summers and P. Rees
  J. Appl. Phys. Vol. 101, March 15, 2007
• “Observations and modification of concentric modulations in the transverse modes of a vertical-cavity surface-emitting laser measured by scanning near-field optical microscopy”
  M. D. Holton, P. R. Dunstan and P. Rees
  J. Appl. Phys. Vol. 101, 023103, 2007.

2006

• “Theoretical investigation of InGaN self-pulsating laser diodes for optical storage applications”
  D.R. Jones, P. Rees, and I. Pierce
  IEE Proceedings Optoelectronics, Volume 153 (6), pp330-337, 2006.
• “Modeling multiple quantum barrier effects and reduced electron leakage
  in red-emitting laser diodes”
  M. R. Brown, R. J. Cobley, K. S. Teng, P. Rees, S. P. Wilks, A. Sobiesierski, P. M. Smowton and P. Blood
  J. Appl. Phys., Volume 100, 084509, 2006.
• “Kinetic Analysis of the Thermal Stability of the Photosynthetic Reaction Centre from Rhodobacter sphaeroides”
  A.V. Hughes, P. Rees, P. Heathcote and M.R. Jones
  Biophys. J., Volume 90, No.4 pp4155-4166, 2006.
• “Synchronisation recovery in unidirectionally coupled semiconductor lasers”
  S. Peters-Flynn, I. Pierce, P.S. Spencer, and P. Rees
  IEE Proceedings Optoelectronics, Volume 153 (1), pp8-12, 2006.

2005

• “Near-field scanning optical microscopy and near-field induced photocurrent investigations of buried heterostructure multiquantum well lasers”
  M.P.Ackland, P.R.Dunstan and P.Rees
  Journal of Microscopy, Volume 220, pp.229-235, 2005.
• “Dynamical characterisation of laser diode subject to double optical feedback for chaotic optical communications.”
  M.W.Lee, P. Rees, K.A.Shore, S.Ortin, L.Pesquera and A.Valle
  IEE Proceedings Optoelectronics, Volume 152 (2), pp97-102, 2005.
• “Analysis of chaos generated by a modulated self-pulsating laser diode.”
  R.P.Walker, P. Rees, I.Pierce, P.S.Spencer and G.W. Roberts
  IEE Proceedings Optoelectronics, Volume 152 (2), pp90-96, 2005.
• “Polychromatic coupled cavity model of passive structures.”
  D. Perkins, P.S.Spencer and P. Rees
  IEE Proceedings Optoelectronics, Volume 152 (2), pp58-65, 2005.
• “Dynamics of the wetting-layer-quantum-dot interaction in InGaAs self-assembled systems”
  D.R. Matthews, H.D. Summers, P.M. Smowton, P. Blood P, P. Rees and M. Hopkinson
  IEEE Journal of Quantum Electronics 41 (3), pp344-350, 2005.

2004

• “Temperature dependence of self-pulsation in compact disc lasers”
  S.A. Lynch, P. McEvoy, J. O'Gorman, P. Rees, W. Elsasser and P. Landais
  IEE Proceedings Optoelectronics, Volume 151 (6), pp496-501, 2004.
• “Laser dynamics in self-oscillating quantum dot systems”
  D.M. Matthews, H.D. Summers, P.M. Smowton, P.Rees and Mark Hopkinson
  Journal of Applied Physics 95(3) pp1036-1041, 2004.

2003

• “Anticipated chaos in a non-symmetric coupled external cavity laser system”
  P. Rees, P.S. Spencer, I. Pierce, S. Sivaprakasam, and K.A. Shore
  Physical Review A 68, 033818, 2003.
• “Nullified time-of-flight lead-lag in synchronization of chaotic external cavity laser diodes”
  S.Sivaprakasam, J.Paul, P.S.Spencer, P.Rees and K.A.Shore
  Optics Letters 28 (16) pp1397-1399, 2003
• “Synchronisation regimes in chaotic optical communication systems”
  I. Pierce, A. Valle, S. Sivaprakasam, P. Rees, P.S. Spencer and K.A. Shore (p.191)
  IEE Proceedings Optoelectronics, Volume 150 (2), pp191-198, 2003
• “Theory of Q-Switching in a Quantum Dot Laser Diode”
  A.Owen, P.Rees, I.Pierce, D.Mathews and H.D.Summers
  IEE Proceedings Optoelectronics, Volume 150 (2), pp152-158, 2003
• “Multi-mode self-pulsation in laser diodes with epitaxially integrated saturable absorber - Mode Competition and Carrier Dynamics”
  I. Pierce, H.D.Summers, P. Rees, and D.R.Jones
  IEE Proceedings Optoelectronics, Volume 150 (2), pp159-162, 2003
• “Polarisation-resolved chaos and instabilities in a vertical cavity surface emitting laser subject to optical injection”
  Y.Hong, P.S.Spencer, S.Bandyopadhyay, P.Rees and K.A.Shore
  Optical Communications 216 (1-3): 185-189, 2003

2002

• INVITED: “Regimes of chaotic synchronization in external-cavity laser diodes”
  S.Sivaprakasam, P.S.Spencer, P.Rees and K.A.Shore
  IEEE Journal of Quantum Electronics 38 (9): 1155-1161, 2002
• “Transition between anticipating and lag synchronization in chaotic external-cavity laser diodes”
  S.Sivaprakasam, P.S.Spencer, P.Rees and K.A.Shore
  Optics Letters 27 (14): 1250-1252, 15 2002
• “Optical injection dynamics of two-mode vertical cavity surface-emitting semiconductor lasers”
  Y.Hong, P.S.Spencer, P.Rees and K.A.Shore
  IEEE Journal of Quantum Electronics 38 (3): 274-278, 2002
• “GHz bandwidth message transmission using chaotic diode lasers”
  J.Paul, S.Sivaprakasam, P.S.Spencer, P,Rees and K.A.Shore
  Electron Lett 38 (1): 28-29 JAN 3 2002