1. National Laboratory of Solid State Microstructures and School of Physics, Nanjing University, Nanjing 210093, China
2. Jiangsu Key Laboratory for Opto-Electronic Technology, School of Physics and Technology, Nanjing Normal University, Nanjing 210023, China
3. Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
4. Collaborative Innovation Center of Solid-State Lighting and Energy-Saving Electronics, Nanjing University, Nanjing 210093, China