1. Yu. G. Shreter, Yu. T. Rebane, V. A. Zykov, and I. G. Sidorov, Wide-Gap Semiconductors (Nauka, St. Petersburg, 2001) [in Russian].
2. Yu. Davidenko, Sovrem. Élektron. 10, 36 (2004).
3. A. N. Kovalev, F. I. Manyakhin, V. E. Kudryashov, et al., Fiz. Tekh. Poluprovodn. (St. Petersburg) 32, 63 (1998) [Semiconductors 32, 54 (1998)].
4. A. G. Drizhuk, M. V. Zaĭtsev, V. G. Sidorov, and D. V. Sidorov, Pis’ma Zh. Tekh. Fiz. 22(11), 23 (1996) [Tech. Phys. Lett. 22, 441 (1996)].
5. Y. Y. Yan, S. B. Zhang, and S. T. Pantelides, Phys. Rev. Lett. 86, 5723 (2001).