Field effect and thermoelectric power on arsenic-doped amorphous silicon

Field effect and thermoelectric power measurements have been made as a function of temp. on a series of As-doped amorphous Si samples prepared by glow discharge decompsistion of silane. At lower temp. field effect screening is by localized states at the Fermi level, whereas at higher temp. 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 < = 5 x 10 exp 11 cm exp --2 eV exp --1. Electrical transport is 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.8 refs.--AA