1. UNAM-Institute of Materials Science and Nanotechnology and National Nanotechnology Research Center, Bilkent University, Ankara 06800, Turkey
2. LUMINOUS! Center of Excellence for Semiconductor Lighting and Displays, Singapore 639798, Singapore
3. Department of Physics, State University of New York at Buffalo, Buffalo, New York 14260, United States
4. Department of Electrical and Electronics Engineering, Department of Physics, Bilkent University, Ankara 06800, Turkey
5. Department of Physics, Bilkent University, Ankara 06800, Turkey
6. School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore