1. Yu. A. Romanov, in Multilayer Semiconductor Structures and Superlattices, Ed. by A. M. Belyantsev and Yu. A. Romanov (Gorki, 1984).
2. A. A. Ignatov and Yu. A. Romanov, Fiz. Tverd. Tela (Leningrad) 17(11), 3388 (1975) [Sov. Phys. Solid State 17, 2216 (1975)]; Phys. Status Solidi B 73, 327 (1976).
3. Yu. A. Romanov and L. K. Orlov, Fiz. Tverd. Tela (Leningrad) 18(3), 728 (1977) [Sov. Phys. Solid State 19, 421 (1978)]; Yu. A. Romanov, L. K. Orlov, and V. P. Bovin, Fiz. Tekh. Poluprovodn. (Leningrad) 12, 1665 (1978) [Sov. Phys. Semicond. 12, 987 (1977)].
4. A. A. Kostenko, O. A. Kuznetsov, V. A. Tolomasov, et al., Dokl. Akad. Nauk SSSR 271, 1360 (1983) [Sov. Phys. Dokl. 28, 670 (1983)].
5. M. C. Wanke, A. G. Markelz, K. Unterrainer, et al., in Physics of Semiconductors, Ed. by N. Scheffter and R. Zimmerman (World Scientific, Singapore, 1996), p. 1791.