1. Department of Materials Science and Engineering and California NanoSystems Institute, University of California Los Angeles, Los Angeles, California 90095, United States
2. Key Lab of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Science, Beijing, 100083, People’s Republic of China
3. Graduate School of Science and Enginnering, Yamagata University, Yonezawa, Yamagata, 9928510, Japan.