Carrier generation and recombination processes in copper-doped germanium photoconductors

Abstract

The current-voltage characteristics of copper-doped germanium photoconductors display an ohmic region at very low electric fields, a region of increasing conductivity at intermediate fields over a good portion of which the characteristic may be represented by I = I 0 exp ( V V 0 ) , and finally a breakdown region with a very rapid increase in conductivity. The ohmic region conductance and the parameter I 0 of the exponential region are generally proportional to the incident photon flux, but V 0 changes only slightly. In the breakdown region the I– V curves are independent of the level of illumination. The results on three samples of varying compensation are consistent with a simple model of carrier generation and recombination kinetics which includes impact ionization generation and three body recombination processes. The nonohmic behavior in the exponential region is on this model attributable to a field dependence of the recombination coefficient and a decrease in the sticking probability (as defined in Lax's giant trap theory of recombination) with electric field intensity is proposed as the responsible mechanism.