Field effect and thermoelectric power on arsenic-doped amorphous silicon

Abstract

Field effect and thermoelectric power measurements have been made as a function of temperature on a series of As-doped amorphous silicon samples prepared by glow discharge decomposition of silane. At lower temperatures field effect screening is by localized states at the Fermi level, whereas at higher temperatures it is by mobile carriers in extended states. The density of localized states at the Fermi level increases as the As density increases, at least partially due to the creation of localized states by As donors. The density of surface states is less than or equal to 5 × 10¹¹ cm⁻² eV⁻¹. Electrical transport is interpreted in a two-channel model, involving transport both in extended states and in a band of localized states lying above the Fermi level, the center of which shifts toward the extended states as the doping concentration increases.