Hall Mobility in Chemically Deposited Polycrystalline Silicon

Hall-mobility measurements have been performed on polycrystalline silicon films deposited on a silicon oxide surface by the thermal decomposition of silane. Samples with doping impurities added during deposition or by diffusion from a doped vapor-deposited oxide showed similar behavior. For both n-type and p-type samples approximately 5 μ thick, the mobility reached a maximum value of about 40 cm2/V sec at a free carrier concentration of about 1018 cm−3 and decreased for both higher and lower carrier concentrations. The observed Hall mobility was generally higher in p-type samples than in n-type samples. The decrease in observed mobility with decreasing carrier concentration is attributed to the effects of high resistivity space-charge regions surrounding grain boundaries in the polycrystalline material. The mobility was seen to increase as the film thickness increased for samples with similar doping, indicating a more ordered structure in thicker films.