1. School of Science, China University of Geosciences, Beijing 100083, China
2. Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
3. School of Mechanical and Electronic Engineering, Wuhan University of Technology, Wuhan, Hubei 430070, China
4. Key laboratory of Semiconductor Materials Science, Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China