1. O. P. Pchelyakov, Yu. B. Bolkhovityanov, A. V. Dvurechenskii, et al., Fiz. Tekh. Poluprovodn. (St. Petersburg) 34, 1281 (2000) [Semiconductors 34, 1229 (2000)].
2. Zh. I. Alferov, Fiz. Tekh. Poluprovodn. (St. Petersburg) 32, 3 (1998) [Semiconductors 32, 1 (1998)].
3. A. I. Yakimov, N. P. Stepina, A. V. Dvurechenskii, et al., Phys. Rev. B 63, 45312 (2001).
4. A. I. Yakimov, N. P. Stepina, A. V. Dvurechenskii, et al., Semicond. Sci. Technol. 15, 1125 (2000).
5. B. I. Shklovskii and A. L. Éfros, Electronic Properties of Doped Semiconductors (Nauka, Moscow, 1979; Springer-Verlag, New York, 1984).