1. College of Information and Communication Engineering, Sungkyunkwan University (SKKU), Suwon, 440-746, Korea
2. School of Electronics, Telecommunications and Computer Engineering, Korea Aerospace University (KAU), Goyang, 412-791, Korea
3. Department of Energy Science, Sungkyunkwan University (SKKU), Suwon, 440-746, Korea
4. Electronic Convergence Materials and Device Research Center, Seongnam, 13509, Korea