1. Key Lab of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, P. R. China
2. Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
3. Faculty of Science, Beijing University of Technology, Beijing 100124, P. R. China
4. Joint Lab of Digital Optical Chip, Wuyi University, Jiangmen 529020, P. R. China