Optical and electrical properties of doped semiconductors in a strong electromagnetic field

A study was made of the influence of the impurity scattering on the absorption of a weak electromagnetic wave in a semiconductor with a nonequilibrium electron population. A consistent theoretical analysis is made allowing for the influence of indirect transitions on the amplification and absorption of a weak field. It is shown that indirect transitions (in which momentum is not conserved) shift the gain maximum toward lower frequencies. The profile of the line of absorption of a weak field is calculated in the presence of an additional strong electromagnetic wave of frequency corresponding to the fundamental absorption region. It is shown that impurity scattering reduces the transparency range and smooths out the singularities of the absorption associated with the gap in the energy spectrum appearing under the action of the strong wave. The electrical conductivity of the semiconductor is calculated in the saturation state. It is shown that the electrical conductivity vanishes at some intensity of the strong wave, i.e., the semiconductor acquires insulating properties.