1. Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
2. School of Electrical and Electronic Engineering, LUMINOUS! Center of Excellence for Semiconductor Lighting and Displays, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Singapore
3. Department of Electrical and Electronics Engineering and Department of Physics, UNAM–Institute of Materials Science and Nanotechnology, Bilkent University, Bilkent, Ankara TR-06800, Turkey
4. Centre for Disruptive Photonic Technologies (CDPT), Nanyang Technological University, Singapore 637371, Singapore