1. Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong SAR 999077, People’s Republic of China
2. Guangdong Provincial Key Laboratory of Optoelectronic Information Processing Chips and Systems, School of Microelectronics Science and Technology, Sun Yat-sen University, Zhuhai 519082, People’s Republic of China
3. Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR 999077, People’s Republic of China
4. Department of Physics and William Mong Institute of Nano, Science and Technology, The Hong Kong University of Science and Technology, Hong Kong SAR 999077, People’s Republic of China