1. School of Advanced Materials and Nanotechnology, Xidian University, 266 Xinglong Section of Xifeng Road, Xi’an 710126, Shaanxi, People’s Republic of China
2. State Key Discipline Laboratory of Wide Band Gap Semiconductor Technology, Xidian University, Xi’an 710071, Shaanxi, People’s Republic of China
3. Key Laboratory for Physical Electronics and Devices of the Ministry of Education & Shaanxi Key Laboratory of Photonic Technique for Information, School of Electronics Science & Engineering, Faculty of Electronic and Information Engineering, Xi’an Jiaotong University, Xi’an 710049, China
4. School of Microelectronics, Xidian University, Xi’an 710071, Shaanxi, China