Absorption of Light by Free Charge Carriers in the Crystalline CdS Under Intense Electron Irradiation

The process of light absorption by free electrons in the crystalline cadmium sulfide under irradiation by a nanosecond electron beam with the current density of 8–100 A/cm² is studied. A superlinear increase in optical absorption is observed if the beam current density is increased from ~8 to 12 A/cm². The nature of light absorption by thermalized electrons corresponds to the scattering on lattice defects. An increase in the exponent of the power dependence of light absorption on the wavelength with increasing beam current density is associated with the single and double ionization of donors and acceptors. It is concluded that accumulation of charge carriers occurs without capture by traps due to their impact ionization by secondary electrons, whose energy in the thermalization stage is comparable with the band gap of the crystal. According to the results of calculations, the capture cross section of electrons by holes at quadratic recombination is ~10^–20 cm², the Auger recombination coefficient is ~10^-31 cm⁶∙s^–1, and the charge carrier concentration is ~1.3∙10¹⁸–1.5∙1019 cm^–3.