Professor David Mowbray

Prof David MowbrayHead of Department

Professor of Physics

Contact details

General

Summary

My research involves the application of a range of optical spectroscopic techniques to study physical processes in III-V semiconductors and related nanostructures and devices. Particular interests are wide band gap materials (AlGaInP and (Al)InGaN) for visible and uv light emitters and quantum dots for high efficiency lasers and novel light emitters. I was the first person to deduce the band structure of AlGaInP, a semiconductor now used as the basis for high efficiency red, orange and yellow LEDs and red lasers. I have developed 1.3 um emitting lasers using InAs self-assembled quantum dots which exhibit extremely low operating currents and high temperature stability. A recent project developed quantum dots lasers on Si substrates, providing the potential for the direct integration of III-V light emitters with Si CMOS electronics.

Qualifications

Physics BA (1981-1984, Hertford College, Oxford University)
Physics DPhil (1984-1989, Hertford College, Oxford University)

Academic Career

PDRA Department of Physics, Oxford University 1987-1989
Junior Research Fellow, Worcester College, Oxford University 1987-1989
Alexander von Humboldt Fellow, Max Planck Institute, Stuttgart, Germany 1989-1990
University Lecturer, Department of Physics, University of Sheffield 1991-1997
EPSRC Advanced Fellowship, Department of Physics, University of Sheffield, 1994-1999
Reader in Physics, Department of Physics, University of Sheffield, 1997-2005
Professor of Experimental Solid State Physics, Department of Physics, University of Sheffield 2005-

Departmental administration

Head of Teaching 2004-2012
Head of Department 2006-2012, Jan 2017-
Chair Equality and Diversity Committee 2012-2016
Coordinator Sheffield-Nanjing Technical University Materials Physics Joint Degree 2013-

University administration

Member of Senate 2006-2012
Faculty Executive Board 2007-2012, Jan 2017-
Faculty of Science Learning and Teaching Committee 2006-2012
University Equality and Diversity Committee 2010-2015

Professional activities

Member of the Institute of Physics
Chair of Institute of Physics Outreach and Public Engagement Network
External Examiner Salford University 2012-2016
External Advisor Open University 2012-2016
External Examiner Newcastle University 2016-

Research

Research Interests

My recent research has focussed on the application of self-assembled quantum dots to produce high efficiency semiconductor lasers. Conventional semiconductor lasers have many desirable properties but their operating current (threshold current) can be high and this current typically increases rapidly with increasing temperature. By using quantum dots as the light emitting region it is possible to reduce significantly both the operating current and the temperature sensitivity of this current.
By optimising the epitaxial growth myself and co-workers were able to produce InAs self-assembled quantum dots lasers emitting at 1.3 um with threshold current densities much smaller than comparable quantum well lasers and at the time the lowest ever reported. Later work applied p-type modulation doping to obtain high stability at room temperature.
More recently the ability of quantum dots to trap charges has been used to fabricated high performance lasers on Si substrates. Growth of III-V semiconductors on Si is very challenging as a large density of defects are produced at the Si / III-V interface. These propagate to the light producing region of the device and significantly degrade its efficiency. By using quantum dots, which prevent carriers migrating to these defects, high light producing efficiency is possible. Other work has used the capping of InAs quantum dots with a thin GaAsSb layer to extend the emission wavelength out to the main telecommunications band at 1.55 um.
A recently announced grant will fund a project to study a new type of quantum dot. These are grown within long nanowires that form from small holes made in an inert layer on a semiconductor substrate. Unlike self-assembled quantum dots, which form at random position, these nanowire quantum dots can be made to form at pre-defined positions. In addition there is considerably more control over their shape and size and it is possible to form stacks with large number of identical dots, allowing the formation of nanoscale lasers. This project is a collaboration with University College London and the University of Warwick.

Recent research funding

EPSRC InAs quantum dot lasers on Si substrates April 2012 – March 2016
Innovate UK Fibre wavelength quantum light sources July 2015 – December 2016
EPSRC Self-catalysed GaAsP/GaAs nanowire quantum dots for silicon-based novel quantum emitters October 2016 – March 2020

Teaching

Current

PHY250 Fourier techniques
PHY119 Nanotechnology
PHY190 Mechanics and Quantum Physics
PHY191 Electricity
Year 2 Physics Tutor
Year 3 project supervision

Recent

PHY250 Electromagnetism
PHY6002 Inorganic Semiconductor Nanotechnology (MSc degree)
Year 4 project supervision

Recent undergraduate projects supervised

The physics of digital photography
The physics of projectiles
Environmental sensing with a Raspberry Pi
Development of a presentation to teach the topic of sound to primary school children
Developing experiments to demonstrate the properties of light

Publications

Key Scientific Publications

Observation of a many-body edge singularity in quantum well luminescence spectra. M S Skolnick, J M Rorison, K J Nash D J Mowbray, P R Tapster, S J Bass and A D Pitt. Phys. Rev. Lett. 58 2130-2133 (1987).

Confined LO phonons in GaAs/AlAs superlattices. D J Mowbray, M Cardona and K Ploog. Phys. Rev. B. 43 1598-1603 (1991).

Valence-band splitting in ordered Ga0.5In0.5P measured by polarized photoluminescence excitation spectroscopy. D J Mowbray, R A Hogg, M S Skolnick, M C DeLong, S R Kurtz and J M Olson. Phys. Rev. B. 46 7232-7235 (1992).

Electronic Band Structure of AlGaInP Grown by Solid-Source Molecular Beam Epitaxy. D J Mowbray, O P Kowalski, M Hopkinson, M S Skolnick and J P R David. Appl. Phys. Lett. 65, p213-215 (1994).

GaInP-AlGaInP Band Offsets Determined from Hydrostatic Pressure Measurements. O P Kowalski, J W Cockburn, D J Mowbray, M S Skolnick, R Teissier and M Hopkinson. Appl. Phys. Lett. 66, p619-621 (1995)

Inverted electron-hole alignment in InAs-GaAs self-assembled quantum dots P W Fry, I E Itskevich, D J Mowbray, M S Skolnick, J Barker, E P O'Reilly, L R Wilson, I A Larkin, P A Maksym, M Hopkinson, M Al-Khafaji, J P R David, A G Cullis, G Hill and J C Clark Phys. Rev. Lett. 84, 733 (2000)

Charged and neutral exciton complexes in individual self-assembled In(Ga)As quantum dots J J Finley, A D Ashmore, A Lemaitre, D J Mowbray, M S Skolnick, I E Itskevich, P A Maksym, M Hopkinson and T F Krauss Phys. Rev. B 63, 073307 (2001)

1.3 m InAs/GaAs multilayer quantum-dot laser with extremely low room-temperature threshold current density I R Sellers, H Y Liu, K M Groom, D T Childs, D Robbins, T J Badcock, M Hopkinson, D J Mowbray and M S Skolnick Electron. Lett. 40, 1412 (2004)

1.3 m InAs/GaAs quantum-dot laser with low-threshold current density and negative characteristic temperature above room temperature T J Badcock, H Y Liu, K M Groom, C Y Jin, M Gutierrez, M Hopkinson, D J Mowbray and M S Skolnick Electron. Letts. 42, 922 (2006)

Room-temperature 1.6 m light emission from InAs/GaAs quantum dots with a thin GaAsSb cap layer H Y Liu, M J Steer, T J Badcock, D J Mowbray, M S Skolnick, F Suarez, J S Ng, M Hopkinson and J P R David J. Appl. Phys. 99, 046104 (2006)

Infrared modulated interlevel spectroscopy of 1.3 mu m self-assembled quantum dot lasers using a free electron laser I R Sellers, D J Mowbray, T J Badcock, J P R Wells, P J Phillips, D A Carder, H Y Liu, K M Groom and M Hopkinson Appl. Phys. Lett. 88, 081108 (2006)

Picosecond carrier dynamics in AllnGaN multiple quantum wells S A Hashemizadeh, J P R Wells, P Murzyn, J Brown, B D Jones, T Wang, P J Parbrook, A M Fox, D J Mowbray and M S Skolnick Appl. Phys. Lett. 87, 232106 (2005)

Enhanced room-temperature quantum-dot effects in modulation-doped InAs/GaAs quantum dots Y D Jang, J Park, D Lee, D J Mowbray, M Skolnick, H YLiu, M Hopkinson, R A Hogg, Appl. Phys. Lett. 95 171902 (2009)

Competitive carrier interactions influencing the emission dynamics of GaAsSb-capped InAs quantum dots Pavarelli, N. Ochalski, T. J. Liu, H. Y. Gradkowski, K. Schmidt, M.Williams, D. P. Mowbray, D. J. Huyet, G. Appl Phys Lett 101 DI 10.1063/1.4769431(2012)

In situ annealing enhancement of the optical properties and laser device performance of InAs quantum dots grown on Si substrates Jonathan R. Orchard1, Samuel Shutts, Angela Sobiesierski, Jiang Wu, Mingchu Tang, Siming Chen, Qi Jiang, Stella Elliott, Richard Beanland, Huiyun Liu, Peter M. Smowton, David J. Mowbray Optics Express March (2016)
https://doi.org/10.1364/OE.24.006196

Books

Chapter on Inorganic Semiconductor Nanostructures in ‘Nanoscale Science and Technology’ edited by R Kelsall, I W Hamley and M Geoghegan Wiley 2005 ISBN: 978-0-470-85086-2

Review articles
Exciton-Phonon interactions in quantum wells and superlattices.
K J Nash and D J Mowbray. J. Lumin. 44 315-346 (1989).

Quantum dots spot single photons
D J Mowbray PHYSICS WORLD 13, 27 (2000)

Self-assembled semiconductor quantum dots: Fundamental physics and device applications
M S Skolnick and D J Mowbray Annual Rev. Mat. Res. 34, 181 (2004)

Recent developments in the physics and applications of self-assembled quantum dots
M S Skolnick and D J Mowbray Physica E-Low Dimensional Sys. and Nanostruct. 21, 155 (2004)

Quantum-dot lasers close in on their quantum-well rivals
D J Mowbray LASER FOCUS WORLD 41, 157 (2005)

New physics and devices based on self-assembled semiconductor quantum dots
D J Mowbray and M S Skolnick J. Phys. D. 38, 2059 (2005)

Public Engagement

Schools Outreach Talks

Electricity (primary school)
Sound (primary school)
Light (primary school)
Electromagnetic spectrum (secondary / 6th Form)
Nanotechnology (6th Form)
Solar Energy (6th Form)
Quantum Mechanics (6th Form)