1. K. V. Shalimova and N. V. Pirogova, Dokl. Akad. Nauk SSSR,139, 938 (1961).
2. N. V. Pirogova, Dokl. Akad. Nauk SSSR,139, 1153 (1961); ibid.,139, 1413 (1961).
3. K. V. Shalimova, V. N. Khirin, and O. I. Korolev, Izv. Vys. Uch. Zav. SSSR, Fiz., No. 1, 80 (1965); (1966); Opt. i Spektr.,21, 1063 (1966).
4. K. V. Shalimova and V. N. Khirin, Abstracts of Reports to the Second All-Union Conference of Photoelectric and Optical Phenomena in Semiconductors [in Russian], Izd. AN USSR, Kiev (1961), p. 152.
5. F. A. Kroger, Physica,7, 1 (1940).