Dr. Li Kwai Hei from Department of Electrical and Electronic Engineering, recipient of the Award for Outstanding Research Postgraduate Student, carried out his research work based on the nanostructuring technique he developed. He has demonstrated the use of nanosphere lithography (NSL) to pattern various novel nano-structures on GaN semiconductors. Compared with other possible top-down approaches for fabricating nanostructures such as e-beam evaporation and focused ion beam, NSL has its predominance in forming close-packed arrays across a large area. Moreover, NSL overcomes resolution issues arising from diffraction limit in optical lithography and even limitation of beam size in electron-beam lithography. The low set-up cost and high throughput also makes NSL potentially suitable for mass production.
Dr. Li Kwai Hei (right) at the Award for Outstanding Research Postgraduate Student presentation ceremony.
Dr. Li has applied nanosphere lithography to nitride-based light-emitting diodes (LEDs) and laser diodes, and achieved significant accomplishment. His investigations led to the possibility of increasing the light extraction efficiency and modifying emission characteristics of LEDs by using an easily-achieved regularly-structuring technique. He also demonstrated the nano-cavities laser structure. Compared with other fabrication techniques, NSL shows great advantages in producing high-density well-defined nano-cavities.
It is generally considered that the standard procedure of NSL would result in tedious close-packed pillar array and does not work for PBG structures and laser cavities. However, Dr. Li has explored new approaches and overcome the patterning restriction of NSL. He has discussed his work recently at several international meetings and attracted wide attention. Without a doubt, his research works are particularly important in tackling two of major concerns in the field of optoelectronics; low light extraction efficiency of LEDs and lack of practical approach for fabrication of high-quality short-wavelength laser cavities.
Dr. Li's thesis work focuses mainly on his original research into the development of a practical nanofabrication approach, termed as nanosphere lithography (NSL). This is of great importance and interest in the nanofabrication, LED and solid-state devices communities. Dr. Li convincingly proves that based on the self-assembling mechanism NSL can be used to create well-defined periodic pattern (2D photonic crystal) for enhancing the light extraction in LED, forming whispering-gallery mode (WGM) circular disk/ring laser microcavities, and for making micro-lens on flip-chip LED.
His experimental results and theoretical analysis can be expected to enhance state-of-the-art design and fabrication of optical devices used in GaN-based photonic applications. After further optimization, this technology should be suitable for making light sources and other optical components in the future.
Dr. Li Kwai Hei (right) and Dr. H.W.Choi, Supervisor (left).