1. R. Dingle, in Festkorperprobleme, Vol. 15 of Advances in Solid State Physics (Pergamon/Vieweg, Braunschweig, 1975), p. 21.
2. A. Hartstein and A. Fowler, in Proceedings of the 13th International Conference on the Physics of Semiconductors, Rome,
1976, p. 741.
3. A. I. Ekimov, A. A. Onushchenko, and V. A. Tsekhomskii, Fiz. Khim. Stekla 6, 511 (1980).
4. I. M. Lifshitz and V. V. Slezov, Sov. Phys. JETP 8, 331 (1959).
5. V. V. Golubkov, A. P. Titov, and E. A. Porai-Koshits, Prib. Tekh. Eksp., No. 1, 215 (1975).