1 State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China; College of Materials Science and Opto-Electronic Technology, College of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China.
2 State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China; College of Materials Science and Opto-Electronic Technology, College of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China. Electronic address: jiyang@semi.ac.cn.