1. School of Optoelectronic Science and Engineering; University of Electronic Science and Technology of China; Chengdu 610054 P. R. China
2. School of Optoelectronic Science and Engineering; University of Electronic Science and Technology of China; State Key Laboratory of Electronic Thin Films and Integrated Devices; University of Electronic Science and Technology of China; Chengdu 610054 P. R. China
3. School of Microelectronics; Xidian University; Xian 710071 P. R. China
4. National Laboratory of Solid State Microstructures; School of Electronic Science and Engineering, and Collaborative Innovation Center of Advanced Microstructures; Nanjing University; Nanjing 210093 P. R. China