1. School of ScienceBeijing University of Chemical Technology Beijing 100029 China
2. School of ScienceMinzu University of China Beijing 100081 China
3. State Key Laboratory on Integrated Optoelectronics, Institute of SemiconductorsChinese Academy of Sciences Beijing 100083 China
4. Center of Materials Science and Optoelectronics EngineeringUniversity of Chinese Academy of Sciences Beijing 100049 China