1. Department of Materials Science and Engineering, Hoseo University, Asan, Chungnam 336-795, South Korea
2. Department of Semiconductor and Display Engineering, Hoseo University, Asan, Chungnam 336-795, South Korea
3. Institute of Materials Science, Technische Universität Darmstadt, Alarich-Weiss-Straße 2, Darmstadt 64287, Germany