1. Physics of Electronic Materials Division, Department of Physics, Faculty of Mathematics and Natural Sciences (FMIPA), Institute of Technology Bandung (ITB), Jl. Ganesha 10, Bandung 40132, Indonesia
2. Department of Physics, University of Diponegoro, Jl. Prof. Soedharto, SH, Tembalang, Semarang 50275, Indonesia
3. Department of Physics, State University of Semarang, Sekaran, Gunungpati, Semarang 50229, Indonesia