Transient establishment of the Dember field in fast photoconductive circuit elements

Abstract

The time τ eef required to establish the Dember electric field E_{D}(t) following the sudden application or removal of incident light or other radiation is examined in general for large surface recombination velocity and illustrated for fast photoconductive circuit elements. The influence of surface scattering on mobility depends strongly on E_{D}(t) because E D results in electrons and holes locating themselves away from the surface. The analysis is subject to the assumptions underlying the ambipolar transport equation and to a single time-constant characterization of the recombination rate. The results show that if τ eff exceeds other times characteristic of the turn-on or turn-off transient, then it enters importantly into determining the transient observed. Specifically, if the product of the steady-state high injection lifetime, the ambipolar diffusion coefficient, and the square of the absorption coefficient of the incident light greatly exceeds unity, then τ eff enters importantly. Otherwise it does not.