Growth of n-type polycrystalline pyrite (FeS_2) films by metalorganic chemical vapour depositon and their electrical characterization

摘要

The compound semiconductor pyrite (FeS_2) has attracted attention as a possible absorber material for thin film solare cells. In this articele it is shown for the first time that polycrystalline pyrite films which noramlly show p-type conductivity, can in situ be doped n-tpye by using cobalt as a dopant abvoe a concentration of 0.3 at/100. The chemical cobalt concentration - determined by high energy heavy ion Rhtherfored backscattering analysis - is proportional to the cobalt-to-iron ratio in the gas phase. The carrier concentrations awre very high (>10~20 cm~-3) and the Seebeck coefficients are low (<70μ V/K), pointing at degenerated semiconductor properties. The carrier transport in the films can be described by the grain barrier limited transport model described by Seto (1975). From the temeprautre dependence of the Hall mobiltiy, barrier heights of 7-37 meV have been determined. The trap density in the grain barriers is about 2×10~13 cm~-2, a value which is much hgiher than in polycrystalline silicon or CdS-films.