1. Department of BIN Fusion Technology; Chonbuk National University; Jeonju 561-756 Korea
2. Department of Physics; Y. S. R. Engineering College of Yogi Vemana University; Proddatur 516 360 India
3. Jeonju Center, Korea Basic Science Institute; Jeonju 561-756 Korea
4. School of Semiconductor and Chemical Engineering, Semiconductor Physics Research Center; Chonbuk National University; Jeonju 561-756 Korea