1. School of electronic engineering and Beijing Key Laboratory of Space-Ground Interconnection and Convergence Beijing University of Posts and Telecommunications Haidian Beijing 100876 P. R. China
2. Key Laboratory of Semiconductor Materials Science Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices, Institute of Semiconductors Chinese Academy of Sciences P.O. Box 912 Beijing 100083 P. R. China
3. Key Laboratory of Microelectronics Devices & Integrated Technology Institute of microelectronics Chinese Academy of Sciences Beijing 100029 P. R. China
4. School of Engineering Beijing University of Technology Beijing 100081 P. R. China
5. Institute of Semiconductors Chinese Academy of Sciences P.O. Box 912 Beijing 100083 P. R. China