XEROGRAPHIC PROPERTIES OF A-SE-TE PHOTOCONDUCTORS

Due to their desirable spectral response, amorphous Se:Te alloys are widely used as commercial xerographic photoreceptor materials. It is shown that the dark decay of the electrostatic surface potential on a corona-charged a-Se:Te alloy photoreceptor occurs via electric field-enhanced xerographic depletion discharge (FEXDD) in which Poole-Frenkel-assisted thermal emission of holes from deep mobility-gap states and their subsequent sweep out generates a negative bulk space charge. A theoretical expression is derived for the dependence of the xerographic depletion time t(d) and the time required for the surface potential to decay to half its value t1/2 on the initial charging voltage V0. Experimental data show good agreement with the theory and enable the Poole-Frenkel coefficient for a-Se:Te to be evaluated. Furthermore, it is shown that at the highest charging voltages, t1/2 actually decreases with V0, which is directly attributable to the FEXDD process. Cycled-up xerographic residual voltage measurements indicate that the saturated residual voltage increases sharply with small Te addition due to an increase in the concentration of deep hole traps. As the Te content is increased beyond approximately 12 wt.% Te, the saturated residual potential starts to decrease. Cycled-up xerographic residual voltage measurements carried out on two double-layer photoreceptors of the Se:Te/Se type when interpreted via the residual voltage expression for a double dielectric structure points to possible interface hole traps between the top Se:Te photogeneration layer and the Se charge transport layer.