  General expressions are obtained for the coefficient of light absorption by
free carriers as well as the intensity of the spontaneous light emission by hot
electrons in multivalley semiconductors. These expressions depend on the
electron concentration and electron temperature in the individual valleys. An
anisotropy of the dispersion law and electron scattering mechanisms is taken
into account. Impurity-related and acoustic scattering mechanisms are analyzed.
Polarization dependence of the spontaneous emission by hot electrons is found
out. At unidirectional pressure applied or high irradiation intensities, the
polarization dependence also appears in the coefficient of light absorption by
free electrons.
