FREQUENCY-DEPENDENT ELECTRICAL BEHAVIOR OF POLYCRYSTALLINE TRIGONAL SELENIUM AND ITS RELATIONSHIP TO XEROGRAPHIC PERFORMANCE OF SELENIUM PARTICLE CONTACT PHOTORECEPTORS

A detailed correlation between the xerographic performance of trigonal selenium binder layers and the dc and low-frequency ac dark conductivity of these photoreceptors and of polycrystalline compactions fabricated from identical starting materials has been established. Studies of the temperature dependence of the ac conductivity of compactions and of xerographic layers as functions of thermal history and ambient gas exposure indicate that heating (∼150 °C) the pigment in oxygen (but not argon or nitrogen) is required to achieve adequate xerographic sensitivity. This heat treatment also converts the original simply activated conductivity to a complicated function of temperature, characterized by a local conductivity maximum near room temperature. From this result a large decrease in xerographic sensitivity (a factor of 2-3) with increasing temperature from 20 to 40 °C was first predicted and subsequently observed. Evidence that these effects are not due to absorption and desorption of weakly bound gases is presented. The frequency and ambient gas dependence of the ac conductivity of compactions and layers indicate that their dc and low-frequency ac conductivity (and thus the layer xerographic properties) are primarily controlled by interparticle barriers and that the thermal history and ambient gas effects modulate these barriers. Key requisites of models constructed to explain this behavior are discussed.