Polycrystalline semiconductors: Structure-property relationships

Without exception the performance of devices based on polycrystalline semiconductors depends on grain boundary effects, Grain boundaries are singularities in the microstructure, characterized by a local perturbation to the bonding and chemical constitution which in rum may result in the formation of states in the forbidden gap which can act as recombination centers and, when charged, barriers to carrier transport. Chemical and structural effects can each have major roles in the formation of barriers at individual boundaries but the mechanisms are only known in general terms. The properties of a polycrystalline ensemble depend on the connectivity of the grain structure. For example conductivity is quite well described by the averaged behavior of grain boundaries, at least far from the percolation threshold. Properties such as breakdown phenomena depend on the occurrence of critically-sized connected links comprised of groups of 'weak' grain boundaries. The grain structure and dopant distributions in polycrystalline semiconductors, and in principle their properties, can be controlled through the processing path and conditions.