1. Jiangsu Provincial Engineering Research Center of Low Dimensional Physics and New Energy, Nanjing University of Posts and Telecommunications, 9 Wenyuan Road, Nanjing 210023, China
2. State Key Laboratory of Silicon and Advanced Semiconductor Materials, Zhejiang University, Hangzhou 310027, China
3. School of Science, Zhejiang University of Science & Technology, Hangzhou 310027, China