1. Y. Seo, S. Lee, I. An, C. Song, J. Jeong, Semicond. Sci. Technol. 24, 115016 (2009)
2. J. Zhu, Z.G. Liu, Appl. Phys. A (2003). doi: 10.1007/s00339-002-2025-0
3. X. Zhao, D. Vanderbilt, Phys. Rev. B 65, 075105 (2002)
4. K. Prabakar, A. Park, N. Cho, W.I. Lee, C.K. Hwangbo, J.G. Lee, C. Lee, Vacuum 82, 1367 (2008)
5. Y. Zhou, N. Kojima, K. Sasaki, J. Phys. D, Appl. Phys. 41, 175414 (2008)