The grain boundary is the main defect acting to produce electrical resistivity values that are higher in as-deposited metallic thin films than in bulk materials. This occurs because the grain size in as-deposited metallic thin films is quite small, on the order of several tens of nm. In monocrystalline semiconductors, the majority charge carrier mobility in thin films is decreased by thermal scattering, scattering by ionized impurities and by charged dislocations. Charged dislocations exert a greater scattering effect on carriers moving perpendicular to the dislocation lines than parallel to them and are more effective scatterers than the equivalent number of ionized impurity atoms. Grain boundaries, by trapping majority charge carriers, act as barriers to the transport of majority charge in semiconductors. The dependence of the majority charge carrier mobility on grain size can be used to distinguish between the effects of intragranular defects and grain boundaries on this mobility. The majority charge carrier mobility in amorphous hydrogenated silicon is limited by the temporary trapping of the majority charge carriers.

The minority charge carrier diffusion length in semiconductors varies as the square root of the grain size and inversely as the square root of the dislocation density in accord with the predictions of a model for minority charge recombination at these defects. Because the diffusion length in a-Si:H is smaller than the absorption length which, in turn, is smaller than the drift length, solar cells of this material are designed to absorb light in regions of non-zero electric field. The...