1. Laboratory of Wide Band-gap Semiconductor Materials, Ministry of Education, Xidian University, Xian, People’s Republic of China
2. Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen, People’s Republic of China
3. Science and Technology on Reliability Physics and Application Technology of Electronic Component Laboratory, Guangzhou, People’s Republic of China
4. School of Materials and Engineer1ing, Xiangtan University, Hunan Xiangtan, People’s Republic of China