1 School of Physics, Xidian University, Xi'an, 710071, People's Republic of China.
2 School of Advanced Materials and Nanotechnology, State Key Discipline Laboratory of Wide Band Gap Semiconductor Technology, Xidian University, Xi'an, 710071, People's Republic of China.
3 School of Microelectronics, Xidian University, Xi'an, 710071, People's Republic of China.
4 School of Telecommunication Engineering, Xidian University, Xi'an, 710071, People's Republic of China.
5 The Ministry of Education Key Laboratory of Micro and Nano Systems for Aerospace, School of Mechanical Engineering, Northwestern Polytechnical University, Xi'an, 710072, People's Republic of China.
6 School of Physics, Xidian University, Xi'an, 710071, People's Republic of China. limengyang@xidian.edu.cn.
7 School of Physics, Xidian University, Xi'an, 710071, People's Republic of China. bwei@xidian.edu.cn.
8 MOE Key Laboratory of Material Physics and Chemistry Under Extraordinary, School of Physical Science and Technology, Northwestern Polytechnical University, Xi'an, 710072, People's Republic of China. wuhongjing@nwpu.edu.cn.