1. V. S. Bagaev, T. I. Galkina, A. I. Sharkov, A. Yu. Klokov, V. P. Martovitskii, V. V. Zaitsev, and Yu. V. Klevkov, Fiz. Tverd. Tela (St. Petersburg) 45(11), 1941 (2003) [Phys. Solid State 45 (11), 2039 (2003)].
2. M. S. Brodin, V. M. Bandura, and M. G. Matsko, Fiz. Tverd. Tela (Leningrad) 24(8), 2411 (1982) [Sov. Phys. Solid State 24 (8), 1369 (1982)].
3. C. F. Klingshirn, W. Maier, and B. Honerlage, Solid-State Electron. 21, 1357 (1978).
4. C. F. Klingshirn and H. Haug, Phys. Rep. 70(5), 315 (1981).
5. C. B. Guillaume, J. M. Debever, and F. Salvan, Phys. Rev. 177(2), 567 (1969).