1. College of Physics and Electrical Information Engineering, Daqing Normal University, Daqing 163000, P. R. China
2. MIIT Key Laboratory for Low-Dimensional Quantum Structure and Devices, School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081, P. R. China
3. School of Mechanical Engineering, Hefei University of Technology Xuancheng Campus, Hefei 230002, P. R. China