Theory of electrical transport and recombination in polycrystalline semiconductors under optical illumination

Abstract

A method for describing electrical transport in polycrystalline material has been developed by solving a current continuity equation that involves drift, diffusion and nonuniform generation rate of electron-hole pairs. By taking the recombination current at the grain boundary interface, at the grain boundary space-charge region, and at the bulk into consideration a theoretical method for grain boundary recombination has also been developed. While attempting to develop the theory we have taken care to include the effects of Shockley-Read-Hall recombination statistics, of trap-assisted recombination statistics, and of the heavy dopings of the semiconductor region(s). On the basis of the present theory the dependence of the grain-boundary potential-barrier height V on the grain size, doping concentrations, and carrier generation rate has been studied in detail. It is found that the effective recombination velocity at the edge of the grain boundary space-charge region is a function of V, and that it increases with grain size until it attains a peak value.