1. State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, People's Republic of China
2. College of Materials Science and Optoelectronic Technology, University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China
3. School of Physics and Optoelectronic Engineering, Xidian University, Xi'an 710071, People's Republic of China