1. Ginzburg, V. L., Izv. Akad. Nauk SSSR, Ser. Fiz., 1947, vol. 11, no.2. p. 165 [in Russian].
2. Motz, H., J. Appl. Phys., 1951, vol. 22, p. 527.
3. Motz, H., Thon, W., and Whitehurst, R.N., J. Appl. Phys., 1953, vol. 24, p. 826.
4. Korkhmazyan, N.A., Izv. AN Arm. SSR, Physics, 1970, vol. 5, p. 287; p. 418 [in Russian].
5. Alikhanyan, A.I., Esin, S.K., Ispiryan, K.A., et al., JETP Letters, 1972, vol. 15, p. 98.