1. State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences 1 , P.O. Box 912, Beijing 100083, China
2. Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences 2 , Beijing 100190, China
3. School of Electronic Science and Engineering, Nanjing University 3 , Nanjing 210093, China
4. International School of Microelectronics, Dongguan University of Technology 4 , Dongguan 523808, China