1. Yanka Kupala State University of Grodno , Grodno 230023 , Belarus
2. B. I. Stepanov Institute of Physics, National Academy of Sciences , Minsk 220072 , Belarus
3. Department of Electrical and Electronics Engineering, Department of Physics , and UNAM–Institute of Materials Science and Nanotechnology , Bilkent University , Ankara 06800 , Turkey
4. LUMINOUS! Center of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, School of Physical and Mathematical Sciences , Nanyang Technological University , 50 Nanyang Ave 639798 , Singapore , Singapore