Current Transport in Doped Polycrystalline Silicon

DC conductivity, photoconductivity, magnetoresistance, and ESR of polycrystalline silicon films have been measured as functions of doping and temperature. Native defect states of about 1018cm-3 distributed mainly in the grain boundary region are reduced with phosphorus doping and completely eliminated at doping ratios above 4×10-5. This defect compensation by dopant atoms results in a decrease of local band bending in the grain boundary as confirmed from the analysis of photoconductivity. A rapid decrease in resistivity occurs around a doping ratio of 3×10-5 at which the density of doped phosphorus atoms starts to approach the native defect density. Carrier transport in doped polycrystalline silicon is found to be well understood in terms of a potential fluctuation model describing the electronic density of state distribution in the energy gap.