The Waterloo Institute for Nanotechnology (WIN) is pleased to present a Distinguished Lecture by Gehan Amaratunga, Professor in the Department of Electrical Engineering at the University of Cambridge.
In-person in QNC 1501!
Registration is required. Please register early as there is limited in-person seating.
Quantum Dots to Light
Abstract
Quantum Dots (QDs) are termed 0-D semiconductors. Their optoelectronic behaviour is governed by size effects which give them characteristics between macro-molecules and nanocrystals. Their size is typically in the 1 -10nm range and are synthesised through wet chemical methods. The main size effect of interest is the lack of any phonon density of states as in a larger semiconductor crystal of a given material. This also leads to a discretised electronic density of states in 3-dimensions. Electronic transitions are hence purely governed by energy absorption or emission. Therefore, any semiconductor which in bulk crystalline form is an indirect gap semiconductor for electronic transitions becomes a pseudo-direct band gap semiconductor in QD form. Additionally, the main energy gap from occupied to unoccupied states (band-gap) is inversely proportional to the size (diameter) of the QD. This opens up a rich vein of material systems to explore for the emission and absorption of light through electronic transitions across the visible spectrum.
The presentation gives an introduction to QD synthesis and design for LEDs and full colour displays. An intriguing ability which QDs enable is the realisation of a full colour palette based on many primaries rather than the Red, Green, Blue emitters to which most displays are limited at present. An advantage of using more than 3 primaries is the opportunity it gives to optimise power consumption in generating a colour range. A significant outcome is the realisation that a rich white light spectrum cane be generated from a single QD-LED smart light by varying the drive voltage, for example. There is a growing body of evidence which shows that the spectrum of day light which is seen has a direct bearing on human health. QD-LED based smart lighting is a route to realising customisable lighting environments which can enhance human wellbeing. The major limitations in the development of QD based optoelectronic devices, including efficient electron and hole transport in the active QD layer, are also discussed.
Biography
Gehan Amaratunga is the 1966 Chair Professor of Engineering at the University of Cambridge, a position he has held for 25 years. During this time he has also been the Chan-Ting Tuan Visiting Professor at Nanyang Technological University, Singapore; Honorary Professor at Peking University Graduate School, Shenzhen; the Chief of Research and Innovation at the Sri Lanka Institute of Nanotechnology (SLINTEC) and a founding academic of the Cambridge University Advanced Research and Education Centre in Singapore (CARES). Currently he is also an Adjunct Professor at Zhejiang University in China. During his career his research interests in materials have spanned nanomaterials, thin film carbon, diamond, nanotubes, and more recently II-VI quantum dots. In the area electronic devices he has made advances in power devices, nanowire devices, field emission devices, photovoltaic devices and made the original proposal and demonstration of the Tunnel FET. He has also contributed to analysing and designing new electrical power systems which incorporate renewable energy generation and are configured on the basis of actively interacting microgrids. Prof Amaratunga was elected a Fellow of the Royal Academy of Engineering in 2004 and awarded its Silver Medal in 2007 (in recognition of the commercial success of start-up companies he had founded). He is also a Fellow of the Royal Society of Arts, the National Academy of Sciences of Sri Lanka and the IET.