1. School of Advanced Materials and Nanotechnology, Xidian University, Xi’an 710071, China
2. Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education & International Center for Dielectric Research, School of Electronic Science and Engineering, Faculty of Electronic and Information Engineering, Xi’an Jiaotong University, Xi’an 710049, China
3. College of Engineering, Xi’an International University, Xi’an 710077, China
4. Key Laboratory of Wide Band-Gap Semiconductor Materials & Devices, Xidian University, Xi’an 710071, China