1. V. G. Valyashko, Sov. Phys. Semicond. 6, 1590 (1973).
2. N. M. Kolchanova, M. A. Sipovskaya, and Yu. S. Smetannikova, Sov. Phys. Semicond. 16, 1418 (1982).
3. G. Lucovsky, A. J. Varga, et al., Solid State Commun. 3, 9 (1965).
4. V. I. Perel’ and I. N. Yassievich, Sov. Phys. JETP 55, 143 (1982).
5. S. Kurnick and J. M. Powel, Phys. Rev. 116, 597 (1956).