1. State Key Laboratory of Superlattices and MicrostructuresInstitute of SemiconductorsChinese Academy of Sciences & Center of Materials Science and Optoelectronics EngineeringUniversity of Chinese Academy of Sciences Beijing 100083 China
2. State Key Laboratory of Precision Measuring Technology and InstrumentsTianjin University Tianjin 300072 China
3. School of Optical and Electronic InformationWuhan National Laboratory for Optoelectronics (WNLO)Huazhong University of Science and Technology Wuhan 430074 China