1. Advanced Convergence Research Center; Daegu Gyeongbuk Institute of Science & Technology (DGIST); Daegu 711-873 Korea
2. Green Energy Research Division; Daegu Gyeongbuk Institute of Science & Technology (DGIST); Daegu 711-873 Korea
3. Department of Physics; Incheon National University; Yeonsu-gu Songdo-dong 12-1 406-772 Incheon Korea