Photoeffects in cadmium sulfide and sulfoselenide powders: A reexamination by microwave photoconductivity

Abstract

Cu doped CdS powders in electrophotographic devices have been characterized using the flash microwave photoconductivity method. The signals representative of these materials exhibited minima, as well as maxima, in microwave absorption, hence conductivity; the former were identified with the slow thermalization of deep trapped electrons, which allowed the trapping characteristics of the samples to be inferred. Correlation of the microwave photoconductivity results with electrophotographic measurement elucidated the role of the trapping states in interfering with electrophotographic response. From temperature and wavelength dependence of the photoconductivity it was inferred that (except at low temperatures) the conduction band is not populated directly on light absorption, even of band-gap wavelengths. A kinetic analysis revealed that the observed decay of the photoconductivity was controlled by hole trapping at the Cu(I) centers in the powder; thus the experimental data could be used to reveal a two-stage mechanism for hole trapping, and some features of the potential surface associated therewith are inferred.