Growth of n-type polycrystalline pyrite (FeS2) films by metalorganic chemical vapour deposition and their electrical characterization

The compound semiconductor pyrite (FeS2) has attracted attention as a possible absorber material for thin film solar cells. In this article it is shown for the first time that polycrystalline pyrite films which normally show p-type conductivity, can in situ be doped n-type by using cobalt as a dopant above a concentration of 0.3 at%. The chemical cobalt concentration - determined by high energy heavy ion Rutherford backscattering analysis - is proportional to the cobalt-to-iron ratio in the gas phase. The carrier concentrations are very high( > 10(20) cm(-3)) and the Seebeck coefficients are low (< 70 mu 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 temperature dependence of the Hall mobility, barrier heights of 7-37 meV have been determined. The trap density in the grain barriers is about 2 x 10(13) cm(-2), a value which is much higher than in polycrystalline silicon or CdS-films. (C) 1999 Elsevier Science B.V. All rights reserved.