Past seminars:
“Recent advances in the research of III-nitride Quantum Dots”
Mark J. Holmes, Lumileds (USA)
27th April 2022 14:00-15:00 UTC/GMT
Semiconductor quantum dots (QDs) are proving to be one of the most promising platforms for the generation of single photons for quantum information processing applications [1]. Amongst the various materials being investigated, III-nitride QDs are of particular interest due to favourable material properties that allow for emission without the requirement of cumbersome cryogenic cooling systems (as are often required for other materials), and also over a wide range of wavelengths. In this presentation I will present an overview of the field and my research on III-nitride quantum dots for single photon emission over the last decade.
[1] Y. Arakawa and M.J. Holmes, Applied Physics Reviews 7, 021309 (2020).
Mark J. Holmes completed his MPhys and DPhil degrees at the University of Oxford, where he studied the optical properties of various III-nitride nanostructures. Since graduating, he moved to The University of Tokyo where he performed a wide range of work on the optical properties of III-nitride quantum dots, in particular for single photon generation. He has recently moved to the USA and is researching LED technologies at Lumileds, LLC.
“Advances in zincblende III-Nitrides grown on 3C-SiC/Si (001) for next-generation visible LEDs“
Dr Stephen Church, Dept of Physics and Astronomy, University of Manchester
19th January 2022 15:00-16:00 UTC/GMT
Phosphor-less RGB InGaN/GaN-based LEDs are being hailed as the ultra-efficient, colour-pure, next generation of commercial lighting, however, intrinsic green-emitting devices have a reduced efficiency when compared to the other colours, despite decades of research [1]. Highly efficient blue LEDs use c-plane wurtzite InGaN/GaN quantum wells (QWs) as the active region, but the efficiency of these heterostructures drops in the green due to a combination of intrinsic electric fields [1], increased defect densities [2] and strong carrier localisation at high indium contents [3].
In this seminar I will present a summary of recent work that aims to overcome this ‘green gap’ by utilising the metastable zincblende (zb) crystal structure of GaN. I will demonstrate the growth of phase-pure zb-GaN epilayers using MOCVD on production line-compatible SiC/Si (001) substrates and show the development of these materials from doped epilayers to novel heterostructures. Through photoluminescence experiments I will establish the advantageous properties of these structures, including an absence of internal electric fields, a fast radiative recombination rate and strongly polarised light-emission.
[1] M. Auf der Maur et al., Phys. Rev. Lett. 116, 027401 (2016).
[2] David, A. et al., Phys. Rev. Appl., 11, 031001 (2019).
[3] Tanner, D. S. P., et al. Phys. Rev. Appl., 13, 044068 (2020).
Dr James Pomeroy, Centre for Device Thermography and Reliability, University of Bristol
20th October 2021 15:00-16:00 UTC/GMT
5G (and future) communications technologies require RF amplifiers with ever higher performance and efficiency. GaN RF high-power transistors are an enabling technology, achieving RF power densities over an order of magnitude higher than previous technologies, becoming the standard for this application. However, there is a thermal management challenge associated with increasing the power density, particularly near to the sub-micron size channel hot spot. Consequently, the performance of GaN HEMTs has been thermally limited, i.e., derated to ensure reliability. We will review how this challenge has been addressed: State of the art thermal characterisation techniques with sub-micron spatial and nano-second temporal resolution which are used to identify thermal bottle necks; direct mapping of the channel electric field distribution, which indicates the hot spot size; improved GaN/substrate thermal interfaces and GaN-diamond integration for improved thermal dissipation. Future challenges associated with nano-scale devices and possible solutions will be discussed.
“Current transport in nitride superlattices”
Prof Jean Yves Duboz, CRHEA-CNRS, Valbonne, France
15th September 2021 15:00-16:00 UTC/GMT
The speaker will investigate the current transport in AlGaN/GaN SL, with a focus on the p materials. The motivation is to solve the problem of the poor p conductivity in p:AlGaN layers. While SLs have been proposed as a solution, He will show that the hole conductivity is not improved in SL in the vertical direction. Benefits can however be found for pseudo vertical devices.
“Indium Nitride: A Potential Material for Hot Carrier Solar Cells?”
Prof Ian R. Sellers, University of Oklahoma
7th July 2021 15:00-16:00 UTC/GMT
Ian Sellers received his Bachelor’s Degree from the Department of Electrical & Electronic Engineering at the University of Liverpool in 1999, a Master’s Degree from the Dept. of Physics at Imperial College London in 2001, and a Ph.D. in Physics from the University of Sheffield in 2004. Between 2004 – 2006 Dr Sellers was a Marie Curie Fellow at CRHEA-CNRS in Valbonne, France. A position that was followed by a three year postdoctoral position in the group of Professor Bruce D. McCombe at the University at Buffalo SUNY. Following his position at SUNY Buffalo, Dr. Sellers joined the Solar Energy and Technology Group as a Senior Research Scientist at Sharp Laboratories of Europe in Oxford, UK where, he was also a Visiting Academic Fellow in the Department of Materials at the University of Oxford. After spending three years in Industry, Dr. Sellers returned to the Academic environment taking a position at the University of Oklahoma in 2011. In addition to being a tenured Professor in Physics and Engineering Physics, Dr. Sellers is the Associate Director of the Oklahoma Photovoltaics Research Institute. Dr. Sellers’ group at OU is focused on the development and investigation of novel quantum-engineered materials and devices for next generation photovoltaics. Specific programs involve hot carrier dynamics in III-V and perovskite systems, defect formation and stability of thin-film CIGS and perovskites solar cells, as well as their suitability for deep space power applications.
“The Polish input to world GaNification”,
31st March 2021 15:00 UTC/GMT
Dr Mike Leszczynski, Unipress, Warsaw
Dr Leszczynski will present recent results from the Warsaw group concerning; the growth of GaN substrates by ammonothermal method, problems of MOVPE and MBE epitaxy (focus on InGaN QWs), blue laser diodes and their arrays: technology and applications. He will also talk about recent and future research projects at Unipress
Mike Leszczynski is the Head of Semiconductor Microstructure Lab in the Institute of High Pressure Physics, Polish Academy of Sciences. He is also Vice president of TopGaN Lasers (spin-off from the Institute) and President (from 2022) of the Polish Society of Crystal Growth. Hi Main interests: nitride semiconductors, defects in crystals, X-ray Diffraction. He is Author and coauthor of about 400 papers, cited about 7000 times (h:35).
“An Illuminating Career in the LED Industry”,
24th March 2021 16:00 UTC/GMT:
Dr Catherine Othick, Luminus Devices Inc, California
Dr Catherine Othick is a Former UKNC Student Member and 2015 ‘Illumineer of the Year’. Dr Othick will discuss some of the commercial applications of LEDs and what it’s like working in Industry.
Dr Othick obtained her PhD in Photon Physics at The University of Manchester in 2011, focusing on nitride semiconductors. She then joined one of the world’s leading manufacturers of nitride LEDs, Lumileds, starting out as a Staff Development Engineer working on product development characterization and was promoted to Senior Staff Development engineer in 2014, and on to Sr Manager in 2018. Whilst at Lumileds, she developed Product Development characterization infrastructure and developed new test capabilities whilst training/supporting test and characterization engineers globally. In 2019 Dr Othick moved to Luminus Devices, Inc. as the Sr Manager of Characterization and in 2020 became Sr Manager of Test and Characterization. Luminus Devices develops and manufactures LED solutions spanning from UVC to NIR. Luminus’s LEDs are used globally in projector displays, commercial and industrial lighting fixtures, theatrical lighting, medical equipment and horticulture lighting fixtures, to name a few.
