Temperature-dependent xerographic depletion discharge studies of a-Se:Te alloys

The time evolution of the surface potential of xerographic photoreceptors charged in the dark can yield valuable information conerning, the underlying thermal generation processes and the energetic distribution of emission centres. Xerographic dark discharge of a-Se :Te films proceeds according to the xerographic depletion discharge (XDD) model. According to this model the depletion time td should be singly activated. We find that for a-Se :Te alloys in the alloying regime 5-1 2wt% Arrhenius plots of td are non-linear and yield characteristic attempt-to-escape frequencies typically 1 8 times greater than phonon frequencies in these materials. This result can be only partially accounted for by the recent fourth-order approximation of the demarcation energy concept. The presence of exponential distributions of emission centres in this material system is shown by the application of the field-enhanced XDD model at constant temperture. A theoretical fit of temperature-dependent data is then achieved by consideration of the occupation function of emission centres close to EF and the temperature dependence of the mobility gap. For the materials studied, the best fit to the experimental data was achieved with EF located at an energy corresponding to half the optical gap from the mobility edges. The thermal generation mechanism is identified as the process C3 -* C30+h followed by C3° C1 + h.