We have characterized the electrical transport properties of neutronhyphen;transmutationhyphen;doped polycrystalline silicon. Zerohyphen;bias measurements of resistance have been made as a function of temperature on both bulk specimens and individual grain boundaries in this material. Below a doping level of sim;2times;1015phosphorus/cm3, the bulk resistance has a nearly Arrhenius behavior with an activation energy of sim;0.55 eV; above this donor concentration the resistivity is markedly curved on an Arrhenius plot with values of slope which decrease with decreasing temperature. Potential probe measurements show that a large spread in grainhyphen;boundary impedances exist in these higherhyphen;doped specimens. We compare our data to theoretical expressions for current flow across grainhyphen;boundary potential barriers and good agreement is observed; these comparisons indicate that the largest grainhyphen;boundary state densities observed in our samples consist of sim;6times;1011available singlehyphen;electronhyphen;states/cm2located within sim;0.2 eV from the center of the forbidden gap. The chemical potential of these grainhyphen;boundary regions is found to lie at midgap, in agreement with previous data on thinhyphen;film polycrystalline silicon. We note that the considerably higher orientationhyphen;independent state densities found in thinhyphen;film polycrystalline silicon contrasts strongly with the present data and suggest the presence of serious contamination effects in previously studied material.
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