1. Institute of Microelectronics, Tsinghua National Laboratory for Information Science and Technology (TNList), Tsinghua University, Beijing 100084, People's Republic of China
2. School of Energy Science and Engineering, University of Electronic Science and Technology of China (UESTC), Chengdu, People's Republic of China
3. Electrical and Computer Engineering, McGill University, Montreal, Quebec H3A 2T8, Canada
4. Virgiltech, Montreal, Quebec H4B 0A1, Canada
5. National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 500Yu Tian Road, Shanghai 200083, China
6. Laboratory of Nano-Fabrication and Novel Devices Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029, China