1. É. M. Epshtein, Fiz. Tverd. Tela (Leningrad) 19, 3456 (1977) [Sov. Phys. Solid State 19, 2020 (1977)].
2. S. V. Kryuchkov and K. A. Popov, Fiz. Tekh. Poluprovodn. (St. Petersburg) 30, 2168 (1996) [Semiconductors 30, 1130 (1996)].
3. S. V. Kryuchkov and E. G. Fyodorov, Laser Phys. 12, 1037 (2002).
4. F. G. Bass, A. A. Bulgakov, and A. P. Tetervov, High-Frequency Properties of Semiconductors with Superlattices (Nauka, Moscow, 1989).
5. S. V. Kryuchkov and G. A. Syrodoev, Izv. Vyssh. Uchebn. Zaved., Radiofiz. 33, 1427 (1990).