1. A. A. Andronov, Submillimeter Lasers Based on Hot Holes in Semiconductors [in Russian] (Institute of Applied Physics, Soviet Academy of Sciences, Gorki, 1968).
2. L. E. Vorob’ev, F. I. Osokin, V. I. Stafeev, and V. N. Tulupenko, JETP Lett. 35, 440 (1982).
3. I. V. Altukhov, M. S. Kagan, and V. N. Sinis, JETP Lett. 47, 164 (1988).
4. I. V. Altukhov, M. S. Kagan, K. A. Korolev, and V. N. Sinis, Zh. Éksp. Teor. Fiz. 103, 1829 (1993) [JETP 76, 903 (1993)].
5. V. G. Belykh, A. T. Dalakyan, V. N. Tulupenko, and D. A. Firsov, Fiz. Tekh. Poluprovodn. 29, 1764 (1995) [Semiconductors 29, 921 (1995)].