1. Department of Materials Science and Engineering, and Inter-University Semiconductor Research Center, Seoul National University, Seoul 08826, Republic of Korea
2. Department of Materials Science and Engineering, KAIST, Deajeon 34141, Republic of Korea
3. SK Hynix Inc., 2091 Gyeongchung-daero, Bubal-eub, Icheon-si, Gyeonggi-do 467-734, South Korea