1. C. A. Klein, T. M. Hardnett, and C. J. Robinson, Phys. Rev. B 45, 12 854 (1992).
2. G. Davies, Rep. Prog. Phys. 44, 787 (1981).
3. Handbook of the Optical Properties of Semiconductors, edited by M. P. Lisitsa (Naukova Dumka, Kiev, 1987).
4. A. I. Lyamkin, E. A. Petrov, A. P. Ershov, G. V. Sakovich, A. M. Staver, and V. M. Titov, Dokl. Akad. Nauk SSSR 302, 611 (1988) [Sov. Phys. Dokl. 33, 705 (1988)].
5. M. B. Gusev, V. G. Babaev, V. V. Khvostov, and Z. Kh. Valiullova, Izv. Ross. Akad. Nauk, Ser. Fiz. 58(1), 191 (1994).