1. State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, and Center of Materials Science and Optoelectronic Engineering, University of Chinese Academy of Sciences , Beijing 100083 , China
2. Department of Electronic and Computer Engineering, The Hong Kong University of Science and Technology , Hong Kong , China
3. School of Integrated Circuits and Electronics, Beijing Institute of Technology , Beijing 100081 , China