1. Key Laboratory of Advanced Structural Materials; Ministry of Education and Advanced Institute of Materials Science; Changchun University of Technology; Changchun 130012 P. R. China
2. State Key Laboratory on Integrated Optoelectronics; Institute of Semiconductors; Chinese Academy of Sciences; Beijing 100083 P. R. China
3. Center of Materials Science and Optoelectronics Engineering; University of Chinese Academy of Sciences; Beijing 100049 P. R. China