Photochemical Effects and the Effect of Oxygen on Photoconducting Cadmium Sulphide Crystals

Single crystals of cadmium sulphide can be activated to give high photo-conductive sensitivity in a variety of ways. Experiment shows that crystals containing a non-stoichiometric excess of cadmium in the form of sulphur vacancies are inherently unstable. Their photoconductivity decays under illumination and on exposure to an ambient atmosphere containing oxygen. This instability can be eliminated by using an activation treatment which does not produce sulphur vacancies. The photochemical effects and the effects of heat treatment in oxygen on a number of differently activated crystals have been investigated with particular reference to the shallow electron trapping effects produced. Further support has been obtained for the ideas advanced in an earlier paper (Woods and Wright 1058) in which an attempt was made to identify the defects responsible for the well-defined peaks in the thermally stimulated, current curve. These ideas are extended in the present paper to account for some aspects of the photochemical decay and the effects of heat treatment in oxygen.