1. National Laboratory of Solid State Microstructures, School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.
2. National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083, China.
3. Synthesis and Characterization of Innovative Materials, Department of Chemistry, Technical University of Munich, Garching bei München 85748, Germany.
4. Department of Electronic Engineering and Materials Science and Technology Research Center, Chinese University of Hong Kong, Hong Kong SAR, China.
5. School of Electronic Science and Technology, Nanjing University, Nanjing 210093, China.