Electrical conductivity and thermoelectric power of substitutionally doped amorphous silicon

Abstract

The thermoelectric power of amorphous silicon prepared by the glow discharge method with a high density (∼8 × 10¹⁸ cm⁻³) of substitutional phosphorous donors varies slowly with temperature and has an unusually large intercept of ∼ 600 μV K⁻¹ in the limit of infinite temperature. While the contribution from extended states above the mobility edge can be interpreted according to the conventional semiconductor formula, the assumption of a single donor level in the localized states distribution is an oversimplification. Also, the metallic formula is not generally valid because of the very large logarithmic derivative of the density of states at the Fermi level. Instead, explicit integrations of the Kubo-Greenwood formulae over energy are required. Using the experimentally determined density of states distribution and the large positive statistical shift, and making physically plausible choices for the energy dependence of the mobility, the essential features of the data can be explained.