Changes in the photosensitivity and dark conductivity of CdS single crystals after illumination at high temperature

The increase of photoconductivity after previous illumination in the temperature range 320–420 K has been investigated. An activation energy of about 0.8 eV for this process, and two energies around 0.4 and 0.7 eV for the recovery process, have been found. In part of the crystals high residual conductivity has been observed as a co-appearing phenomenon. At 300 K the enhanced photosensitivity persists for a period of longer than 10⁵ s. It is shown that the enhanced photosensitivity is not connected with the destruction of donor-acceptor pairs. As a possible explanation the mechanism of generation of Frenkel pairs in the presence of free carriers is suggested.