1. State Key Laboratory of Integrated Optoelectronics College of Electronic Science and Engineering Jilin University 2699 Qianjin Street Changchun 130012 P. R. China
2. Laboratory of the Ministry of Education Institute of Applied Physics and Materials Engineering University of Macau Avenida da Universidade Taipa Macao SAR 999078 P. R. China
3. School of Materials Science and Engineering Peking University Beijing 100871 P. R. China