1 Key Laboratory of Semiconductor Materials Science, Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
2 Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
3 School of Integrated Circuits and Electronics, MIIT Key Laboratory for Low-Dimensional Quantum Structure and Devices, Beijing Institute of Technology, Beijing 100081, China
4 Engineering Research Center for Semiconductor Integrated Technology, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
5 Fachgebiet Angewandte Nanophysik, Institut für Physik & IMN MacroNano, Technische UniversitätIlmenau, Ilmenau 98693, Germany
6 e-mail: yueshizhong@semi.ac.cn
7 e-mail: wangzj@semi.ac.cn
8 e-mail: yong.lei@tu-ilmenau.de