1. Key Laboratory of Physical Electronics and Devices, Ministry of Education, School of Electronic Science and Engineering, Xi'an Jiaotong University 1 , Xi'an, Shaanxi 710049, People's Republic of China
2. Institute of Wide Band Gap Semiconductors, School of Electronics and Information Engineering, Xi'an Jiaotong University 2 , Xi'an 710049, People's Republic of China
3. College of Information Engineering, Nanyang Institute of Technology 3 , Nanyang 473000, People's Republic of China