1. Key Laboratory for Micro/Nano Optoelectronic Devices of Ministry of Education & Hunan Provincial Key Laboratory of Low-Dimensional Structural Physics and Devices, School of Physics and Electronics, Hunan University, Changsha 410082, People’s Republic of China
2. Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, 100190, People’s Republic of China
3. Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, People’s Republic of China
4. Department of Physics and Astronomy and Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, Tennessee 37235, United States