1. Luminous! Center of Excellence for Semiconductor Lighting and Displays; School of Electrical and Electronic Engineering; Nanyang Technological University; Nanyang Avenue Singapore 639798 Singapore
2. Department of Electrical and Electronics Engineering; Abdullah Gul University; Kayseri 38039 Turkey
3. Department of Electrical and Electronics Engineering; Department of Physics; UNAM - Institute of Materials Science and Nanotechnology; Bilkent University; Bilkent Ankara 06800 Turkey
4. School of Physical and Mathematical Sciences; Nanyang Technological University; Nanyang Avenue Singapore 639798 Singapore