1. State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, CAS, 200050 Shanghai, China
2. School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 Singapore
3. Department of Physics, University of Shanghai for Science and Technology, 200093 Shanghai, China
4. State Key Laboratory of Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 200083 Shanghai, China
5. Photonics and Semiconductor Nanophysics, Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
6. Department of Microtechnology and Nanoscience, Chalmers University of Technology, 41296 Gothenburg, Sweden