1. E. M. Shishonok, T. Taniguchi, K. Watanabe, H. Haneda, and H. Kanda, Diamond Relat. Mater. 12, 1133 (2003).
2. E. M. Shishonok, Zh. Prikl. Spektrosk. 71, 803 (2004).
3. K. Era and O. Mishima, Mater. Res. Soc. Symp. Proc. 162, 556 (1990).
4. E. M. Shishonok and J. W. Steeds, Abstracts of the International Conference “Doping Issues in Wide Band-Gap Semiconductors,” Exeter, United Kingdom, 2001 (Exeter, 2001), p. 7.
5. N. D. Tyapkina, M. M. Krivopolenova, and V. S. Vavilov, Fiz. Tverd. Tela (Leningrad) 6(7), 2192 (1964) [Sov. Phys. Solid State 6 (7), 1732 (1964)].