1 Laboratory of Solid-State Optoelectronics Information Technology, 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 College of Electronic and Communication Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
4 State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
5 School of Physics, Changchun Normal University, Changchun 130022, China
6 Physics Department, Lancaster University, Lancaster LA1 4YB, UK