1. School of Physics, Xidian University, 2 South Taibai Road, Xi’an 710071, Shaanxi, China
2. Discipline Laboratory of Wide Band Gap Semiconductor Technology, School of Microelectronics, Xidian University, 2 South Taibai Road, Xi’an 710071, Shaanxi, China
3. Advanced Interdisciplinary Research Center for Flexible Electronics, Xidian University, 2 South Taibai Road, Xi’an 710071, Shaanxi, China