1. School of Electronics and Information Engineering, Hebei University of Technology, Tianjin 300401, China
2. State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083, China
3. Zhejiang Provincial Key Laboratory of Advanced Microelectronic Intelligent Systems and Applications, Hangzhou 310027, China