Electrode-Limited and Space-Charge-Limited Transient Currents in Insulators

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Abstract
The equations governing the transient-current flow in insulating crystals are solved for two categories of boundary conditions corresponding to situations in which the current is partly space-charge controlled and partly electrode limited. The carrier reservoir at the injecting electrode is assumed to arise from photo-excitation by a pulse of highly absorbed light. In one category, the light intensity is taken to be sufficiently strong such that initially the current is completely space-charge limited. The time dependence of the current after the collapse of the carrier reservoir is calculated, with the time interval elapsed between the onset of the light pulse and the reservoir collapse taken as a parameter. The other category considered corresponds to sufficiently weak pulse excitation such that the field at the illuminated electrode is never zero. The duration of the pulse for this category is assumed to be short compared to the carrier transit time. The time and voltage dependence of the current is calculated in this case in the presence of surface recombination. Both categories of boundary conditions are often encountered in practice, and a comparison between theory and experiment is expected to yield valuable information on carrier generation and recombination processes at the surface.

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