1. CAS Key Laboratory of Nanophotonic Materials and Devices, CAS Key Laboratory of Standardization and Measurement for Nanotechnology, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing 100190, China.
2. Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China.
3. Department of Electrical Engineering, Ginzton Laboratory, Stanford University, Stanford, CA, USA.
4. The Institute of Physics, Chinese Academy of Sciences, P.O. Box 603, Beijing, China.
5. QTF Centre of Excellence, Department of Electronics and Nanoengineering, Aalto University, FI-02150 Espoo, Finland.
6. Wuhan National Laboratory for Optoelectronics and School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, China.
7. ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain.
8. ICREA-Institució Catalana de Recerca i Estudis Avançats, Passeig Lluís Companys 23, 08010 Barcelona, Spain.