1. Division of Physics and Applied Physics School of Physical and Mathematical Sciences Nanyang Technological University 21 Nanyang Link Singapore 637371 Singapore
2. LUMINOUS! Centre of Excellence for Semiconductor Lighting and Displays The Photonics Institute School of Electrical and Electronic Engineering Nanyang Technological University Singapore 639798 Singapore
3. School of Precision Instruments and Optoelectronics Engineering Tianjin University Tianjin 300072 China
4. School of Materials Science and Engineering Nanyang Technological University Singapore 639798 Singapore
5. Department of Electrical and Electronics Engineering Department of Physics UNAM—Institute of Materials Science and Nanotechnology Bilkent University Ankara 06800 Turkey