1. State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
2. Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
3. School of Electrical Engineering, Tiangong University, No. 399, Binshuixi Road, Xiqing District, Tianjin 300387, China
4. School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom