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