1. Guangxi Key Laboratory of Optoelectronic Information Processing, School of Electronic Engineering and Automation, Guilin University of Electronic Technology, Guilin, Guangxi 541004, China
2. State Key Discipline Laboratory of Wide Band Gap Semiconductor Technology, School of Microelectronics, Xidian University, Xi’an, Shanxi 710071, China
3. College of Science, Xi’an Shiyou University, Xi’an, Shaanxi 710065, China