Understanding carrier trapping in multicrystalline silicon

The physical origin of minority carrier trapping centers in multicrystalline silicon is explored in both gettered and non-gettered material. The experimental evidence suggests that there are two types of trap present. One species can be removed by gettering and is related to the presence of boron-impurity pairs or complexes. The other type is impervious to gettering and is correlated to the dislocation density. Annealing experiments reveal that the trapping centers caused by boron-impurity complexes can be dissociated, and that these trapping centers do not contribute to recombination. The effect of trapping centers on open-circuit voltage is shown to be negligible when the trap density is less than the dopant density.