State Key Laboratory of Superlattices and Microstructures Institute of Semiconductors Chinese Academy of Sciences Beijing 100083 China;
Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology Department of Physics School of Science Tianjin University Tianjin 300354 China;
Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology Department of Physics School of Science Tianjin University Tianjin 300354 China;
Suzhou Institute of Nano-Tech and Nano-Bionics Chinese Academy of Sciences Suzhou 215123 China;
State Key Laboratory of Superlattices and Microstructures Institute of Semiconductors Chinese Academy of Sciences Beijing 100083 China;
State Key Laboratory of Superlattices and Microstructures Institute of Semiconductors Chinese Academy of Sciences Beijing 100083 China;
Materials Science Division Lawrence Berkeley National Laboratory Berkeley 94720 USA;
