1. State
Key Laboratory for Superlattices and Microstructures, Institute of
Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
2. College
of Materials Science and Optoelectronic Technology, University of Chinese Academy of Sciences, Beijing 100029, China
3. Department
of Electronic and Computer Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, China