1. Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
2. Nanobiophotonic Center, State Key Lab Incubation Base of Photoelectric Technology and Functional Materials, Institute of Photonics & Photon-Technology, Northwest University, Xi’an 710069, China
3. Division of Materials Science, School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798
4. State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
5. NOVITAS, Nanoelectronics Centre of Excellence, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, 639798.