1. Department of Electrical and
Electronics Engineering, Department
of Physics, UNAM - Institute
of Materials Science and Nanotechnology, Bilkent University, Ankara 06800, Turkey
2. Department
of Physics, Abant Izzet Baysal University, Bolu 14280, Turkey
3. LUMINOUS! Center of Excellence
for Semiconductor Lighting
and Displays, School of Electrical
and Electronic Engineering, School
of Physical and Mathematical Sciences, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Singapore