1. Key Laboratory of Wide Band-Gap Semiconductor Materials and Devices, Xidian University, Xi’an, China
2. Department of Integrated Circuit Design, Institute of Microelectronics Technology, Xi’an, China
3. School of Physics and Information Engineering, Shanxi Normal University, Taiyuan, China
4. Nanofabrication Facility of Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou, China