1. State Key Laboratory for 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 100049, China
3. Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences 3 , Changchun 130033, China