Institution: | a Applied Physics Department, Laboratory for Optoelectronic Materials and Optoelectronic Devices, Shanghai Jiao Tong University, Shanghai 200030, People's Republic of China b Electrical Engineering Department, National Laboratory on Local Fiber-Optic Communication Networks and Advanced Optical Communication Systems, Shanghai Jiao Tong University, Shanghai 200030, People's Republic of China c Research Center for Advanced Materials and National Laboratory for Infrared Physics, Shanghai Institute of Technological Physics, Chinese Academy of Sciences, Shanghai 200083, People's Republic of China d National Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, People's Republic of China |