Infrared Quenching and a Unified Description of Photoconductivity Phenomena in Cadmium Sulfide and Selenide

Infrared quenching, superlinearity, temperature dependence, and slow $S$-shape growth of photocurrent in cadmium sulfide and cadmium selenide crystals may all be associated with the filling and emptying of a specific set of defect levels, as indicated by the location of the calculated electron Fermi level. Infrared quenching of photoconductivity occurs only when the Fermi level lies less than 0.8 ev from the conduction band in CdS, or less than 0.6 ev in CdSe; superlinear photoconductivity occurs only when the Fermi level varies between 0.6 and 0.8 ev from the conduction band in CdS, or between 0.3 and 0.6 ev in CdSe; the photosensitivity decreases rapidly as the Fermi level drops further than 0.6 ev from the conduction band in CdS with increasing temperature, or further than 0.3 ev in CdSe; a slow, $S$-shaped growth of photocurrent is observed when the Fermi level rises between 0.8 and 0.6 ev from the conduction band in CdS, or between 0.6 and 0.3 ev in CdSe.