1. School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798
2. LUMINOUS! Center of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798
3. Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
4. Department of Electrical and Electronic Engineering, College of Engineering, Southern University of Science and Technology, 1088 Xue-Yuan Road, Shenzhen, Guangdong 518055, China