1. Center for Solar Energy Research and Applications Middle East Technical University Ankara 06800 Turkey
2. Micro and Nanotechnology Program of Graduate School of Natural and Applied Sciences Middle East Technical University Ankara 06800 Turkey
3. Physics Department I.D. Bilkent University Ankara 06800 Turkey
4. Electrical and Electronics Engineering Department TOBB University of Economics and Technology Ankara 06560 Turkey
5. Physics Department Middle East Technical University Ankara 06800 Turkey