1. 1Department of Electrical and Electronics Engineering, Department of Physics, Institute of Materials Science and Nanotechnology, and UNAM-National Nanotechnology Research Center, Bilkent, Ankara Turkey 06800
2. 2Department of Electrical and Electronics Engineering, Department of Physics, Institute of Materials Science and Nanotechnology, and UNAM-National Nanotechnology Research Center, Bilkent, Ankara Turkey 06800 and Luminous! Center of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, School of Physical and Mathematical Sciences, School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798