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 possi ble absorber material for thin film solar cells. In this article it is show n 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 dopan t above a concentration of 0.3 at%. The chemical cobalt concentration - det ermined by high energy heavy ion Rutherford backscattering analysis - is pr oportional to the cobalt-to-iron ratio in the gas phase. The carrier concen trations are very high( > 10(20) cm(-3)) and the Seebeck coefficients are l ow (< 70 mu V/K), pointing at degenerated semiconductor properties. The car rier transport in the films can be described by the grain barrier limited t ransport model described by Seto (1975). From the temperature dependence of the Hall mobility, barrier heights of 7-37 meV have been determined. The t rap 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 Else vier Science B.V. All rights reserved.