1. Boltivets, N. S., Drobyazko, V. P., Mityurev, V. K.: Sov. Phys. Semicond. 2 (1969) 867.
2. Abdullaev, G. B., Guseinova, D. A., Kerimova, T. G., Nani, R. Kh.: Phys. Status Solidi (b) 54 (1972) K115.
3. Allakhverdiev, K. P., Antonov, V. B., Nani, R. Kh., Salaev, E. Yu.: Sov. Phys. Semicond. 5 (1972) 2080.
4. Aresti, A., Congiu, A.: Phys. Status Solidi (a) 16 (1973) K55.
5. Fiejeta, H., Okada, Y.: Jpn. J. App. Phys. 13 1974) 1823.