1. School of Physics, Xidian University, Xi’an, 710071, China
2. National Key Laboratory of Wide Bandgap Semiconductor Devices and Integrated Technology, School of Microelectronics, Xidian University, Xi'an, 710071, China
3. College of Chemical Engineering and Technology, Tianshui Normal University, Tianshui 741001, China
4. School of Materials and Chemical Engineering, Xi’an Technological University, Xi’an 710032, Shaanxi, China