Poroshin V. Optical properties of the electron gas in semiconductors with a complex band structure

The thesis presents results of investigation of the effects caused by the band structure in the processes of scattering and non-linear reflection and absorption of light that are related to the free carriers in semiconductors with the degenerate and multi-valley spectrum. For the semiconductors with a degenerate valence band there have been found for the first time a new effect predicted earlier theoretically and consisting in non-screened single-particle light scattering by holes, unusual (non-root like) dependence of the plasma frequency of holes on their concentration, and asymmetric shape of the plasma light scattering line. Their nature is explained by contribution of transitions between the subbands of light and heavy holes into the crystal permittivity. A number of new effects in the light scattering under the conditions of elastic uniaxial deformation of semiconductors has been found: the Raman IR light scattering connected with transitions of holes between the valence band extrema split by deformation, an increase of the plasma frequency and decrease of asymmetry of the plasma line. For the first time, an influence of a degenerate and multi-valley energy spectrum on the processes of light absorption and refraction under the conditions of strong heating of carriers by a light wave field has been studied. There have been found non-linearity of light absorption at the direct intersubband optical transitions in the semiconductors with the degenerate valence band, various non-linear optical phenomena in the multi-valley semiconductors (anisotropy and non-linearity of absorption of an intense IR radiation of a CO2 laser, the birefringence and four-wave interaction phenomena induced by light). They have been explained by redistribution of "hot" electrons among equivalent valleys. For this light wavelength and temperatures of 300 and 80 K the third order non-linearity constant has been determined. The dependencies of the non-linearity constant on the free electron concentration, crystal temperature and IRlight wavelength, calculated for n-Ge have been presented.