1. Hunan Key Laboratory of Nanophotonics and Devices, School of Physics, Central South University, Changsha 410083, P. R. China
2. School of Microelectronics, Southern University of Science and Technology, Shenzhen 518055, P. R. China
3. Department of Physics, College of Sciences, National University of Defense Technology, Changsha 410073, P. R. China
4. Institute of Micro/Nano Materials and Devices, Ningbo University of Technology, Ningbo 315211, P. R. China
5. Physical Sciences and Engineering Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
6. College of Energy and Power Engineering, Changsha University of Science and Technology, Changsha 410114, P. R. China