1. National
Laboratory of Solid State Microstructures, School of Electronic Science
and Engineering, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
2. School
of Microelectronics, Xidian University, Xian 710071, China
3. Beijing
Key Laboratory of Novel Thin Film Solar Cells, Renewable Energy School, North China Electric Power University, Beijing 1002206, China
4. Department
of Physics, Southeast University, Nanjing 211189, China