1. School of Materials Science and Engineering Zhengzhou University Zhengzhou 450052 China
2. State Key Laboratory of Superlattices and Microstructures Institute of Semiconductors Chinese Academy of Sciences Beijing 100083 China
3. Center of Materials Science and Optoelectronics Engineering University of Chinese Academy of Sciences Beijing 100049 China
4. Henan Institute of Advanced Technology Zhengzhou University Zhengzhou 450052 China