1. Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569 Stuttgart, Germany
2. School of Semiconductor and Chemical Engineering, Jeonbuk National University, Jeonju 54896, Republic of Korea
3. LG Innotek Co. Ltd., Seoul 07796, Republic of Korea
4. Department of Materials Science and Engineering, Chonnam National University, Gwangju 61186, Republic of Korea