Opto-electronic processes at grain boundaries in polycrystalline semiconductors

A study has been made of recombination mechanisms at grain boundaries in (n-type) polycrystalline semiconductors under optical illumination. The results have been correlated with the minority carrier lifetime (τ) in the material. The recombination velocity at grain boundaries is enhanced by the band bending or diffusion potential (Vd) adjacent to the boundaries. Under illumination, the population of the interface states is altered considerably from its dark level and as a result, Vddecreases to that value which maximizes recombination (equal concentrations of electrons and holes at the boundary). This means that τ decreases with Nd. The dependence of τ on the doping concentration (Nd), grain size (d) and interface state density (Nis) at the grain boundaries in (n-type) polycrystalline semiconductors has been calculated analytically.