1. Department of Semiconductor Science & Technology and SPRC, Chonbuk National University, Duckjin‐Dong, Duckjin‐ku, Chonju 561‐756, Korea
2. Department of Chemical Engineering, Semiconductor Physics Research Center, Chonbuk National University, Duckjin‐Dong, Duckjin‐ku, Chonju 561‐756, Korea