1. Key Laboratory of Ministry of Education for Wide Band-Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071, People's Republic of China
2. School of Physics and Optoelectronic Engineering, Xidian University, Xi'an 710071, People's Republic of China
3. College of Chemistry and Chemical Engineering, Baoji University of Arts and Sciences, Baoji 721013, People's Republic of China
4. Faculty of Information Engineering and Automation, Kunming University of Science and Technology, Kunming 650051, People's Republic of China