Nanostructures possess properties that do not exist in bulk materials and are being harnessed to improve the performance of electronic and optoelectronic devices. In this talk, I will illustrate the use of nanostructures applied to ZnO and GaN for optoelectronic applications. The greatest challenge for ZnO in optoelectronic application is obtaining stable p-type conductivity. We have successfully demonstrated stable p-type doping with potassium as the acceptor using solution growth method or aqueous phase deposition. This is successfully applied to the fabrication of a ZnO p-n junction core-shell nanorod LED. ZnO single crystalline nanorods are grown with diameters in the range of 80 – 120 nm and length of 1 to 2 µm long on GaN. The low value of lattice mismatch between the two wurtzite semiconductor, about 1.8%, results in no dislocation being found in the nanorods. The second application of nanostructures is in improving the crystal quality of GaN epitaxial layer. GaN is usually grown on sapphire as the substrate but is increasingly grown on Si to reduce cost. However, the lattice mismatch of GaN on both substrates results in a high dislocation density on the order of 108 to 109 cm-2. The use of nanostructure-patterned template is found to reduce the dislocation density by an order of magnitude as well as to reduce strain. This has led to an improvement of the photoluminescence efficiency of quantum wells build on the GaN layers.
Chua Soo Jin is Professor of Optoelectronics at the Department of Electrical and Computer Engineering, National University of Singapore (NUS). Concurrently, he serves as the Deputy Director of the Singapore-MIT Alliance (SMA), a position he has held since the Alliance was formed in 1999. He served as Executive Deputy Director of the Institute of Materials Research & Engineering (IMRE) from 2005 -2010 and is a Principal Fellow of the Institute. He conducts research on GaN MOCVD and ZnO growth by solution method. His research area is in optoelectronics devices and applications and has published over 400 papers in international journals and authored/co-authored 35 patents with 22 of them granted and 7 licensed. His h-index is 36 as recorded in ISI Web of Knowledge. He co-authored a book on Mathematical Physics and contributed to four book chapters. He has received awards for Outstanding Contribution to Research, Excellent Teacher and also as an Outstanding University Researcher in 1996, 1998 and 1999 respectively. He is the inventor of the Quantum Dot White LED and first to demonstrate the Quantum Dot Photodetector. He was the Assistant Director of the Institute of Microelectronics (IME) from 1990-95, when it was first formed in 1990 and established its wide industry contacts and research collaborations with the tertiary institutions during its first five formative years. Prof. Chua is Sr. member of IEEE and the Optical Society of America. He served as Chairman of IEEE, Singapore Chapter from 1984 to 1986 and as Chairman of Education Committee, Region 10 from 1987 to 1988 and Vice-chairman of SPIE from 95-97.
Contact Person: Zhuang Honglei, hlzh@sjtu.edu.cn