1. School of Resources, Environment and Materials, Guangxi University, Nanning 530004, China
2. Optoelectronic System Laboratory, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
3. Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China
4. School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing 100049, China