School of Physical and Chemical Sciences, Te Kura Matū Seminar Series

Why are GaN LEDs so bright when the dislocation density is so high?


Professor Sir Colin Humphreys CBE FRS FREng.


School of Engineering and Materials Science Queen Mary University of London, United Kingdom

Time & Place

Fri, 20 Sep 2019 11:00:00 NZST in Room 701, West Building

All are welcome


A longstanding puzzle was why InGaN/GaN blue, green and white quantum well LEDs were so bright when the dislocation density is so high. The GaN science community all thought they knew the answer and the scientific reasons looked convincing. One of my research students showed them all to be wrong, but what is the correct answer? This was the start of a fascinating detective story to understand the atomic structure of InGaN quantum wells and how the electrons and holes are localised within them. It turns out that the electrons and holes are localised by different mechanisms. We will then look at the challenging scientific problems that had to be solved to grow low-cost GaN LEDs on large-area silicon wafers, which we then commercialised (another talk!). InGaN and GaN are amazing semiconductors with some unique properties. Optical and electronic devices made from them could save a massive 25% of the electricity we use.

All Welcome


Colin is Professor of Materials Science at Queen Mary University of London; Distinguished Research Fellow at the University of Cambridge; and a Fellow of Selwyn College, Cambridge. He is a Fellow of the Royal Society and a Fellow of the Royal Academy of Engineering. He was knighted in 2010 for “services to science”. He founded the Cambridge Centre for Gallium Nitride (GaN) and set up two spin-off companies to exploit the research of his group on low-cost LEDs for home and office lighting. The companies were acquired by Plessey, which is manufacturing LEDs based on this technology at their factory in Plymouth, UK. He founded the Cambridge/Rolls-Royce Centre for Advanced Materials for Aerospace. Materials developed in the Centre are now flying in Rolls-Royce engines. He recently set up a new company, Paragraf, to exploit the research of his group on graphene, which promises to revolutionise a wide range of products including sensors, solar cells and electronic devices. Paragraf moved into premises in 2018, is already employing 21 people and has filed 8 patents. Its first product is a Hall effect sensor for measuring magnetic fields. In his limited spare time he writes on science and religion and is the author of The Miracles of Exodus (Harper Collins, 2003), which has been translated into German and Portuguese and has an Audio edition, and The Mystery of the Last Supper: Reconstructing the Final Days of Jesus. (Cambridge University Press, 2011), which has been translated into Russian, German, Portuguese, Japanese and Greek, and has a South Asian edition.

More information here.