POLYCRYSTALLINE BETA-FESI2 THIN-FILMS ON NON-SILICON SUBSTRATES

beta-FeSi2 films of 600 to 630 nm thickness are prepared by co-evaporation of iron and silicon on various glass and sapphire substrates. Stress induced cracks arising from the crystallization of the amorphous layers can be avoided using glass materials with a thermal expansion coefficient slightly above that of beta-FeSi2, Si and FeSi precipitates arranged in layers parallel to the substrate can be attributed to inhomogeneities of the atomic ratio Si/Fe caused by irregular evaporation rates. Nucleation and grain growth of beta-FeSi2 are studied by heating up the amorphous films either slowly or rapidly. A significantly higher nucleation rate is found in the rapid heating process which is interpreted using the model of homogeneous nucleation. Crystallization at a high deposition temperature of 800-degrees-C gives a fine-grained, columnar grain structure. beta-FeSi2 films crystallized at a low temperature of 400-degrees-C/15 h exhibits a considerable subband absorption probably due to defect states in the band gap. With increasing annealing temperature the subband absorption as well as the electrical conductivity decrease significantly. This is interpreted by the reduction of the acceptor density of the p-type semiconducting material.