1. School of Microelectronics and State Key Discipline Laboratory of Wide Bandgap Semiconductor Technology, Xidian University, Xi'an 710071, China
2. School of Advanced Materials and Nanotechnology, Xidian University, Xi'an 710071, People's Republic of China
3. School of Electronic Science and Technology and State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, China