1. Research and Development Center for Solid State Lighting, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
2. University of Chinese Academy of Sciences, Beijing 100049, China
3. Beijing Engineering Research Center for the 3rd Generation Semiconductor Materials and Application, Beijing 100083, China
4. State Key Laboratory of Solid State Lighting, Beijing 100083, China
5. State Key Laboratory for Artificial Microstructure and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China