1. Department of Materials Science and Engineering, Optoelectronics Convergence Research Center, Chonnam National University, Gwangju 500 757, South Korea
2. Thin Film Materials Laboratory, Department of Physics, Shivaji University, Kolhapur 416 004 M.S., India
3. Department of Electronics and Computer Engineering, College of Engineering, ICT Convergence Research Center for Smart Appliances, Chonnam National University, Gwangju 500 757, South Korea