Some properties of Cr_xV_1−xSi₂ and Cr_xMo_1−xSi₂ thin films

CrSi₂ which crystallizes in the hexagonal C40 structure type is reported to be a semiconductor with a bandgap of about 0.35 eV. On the other hand, VSi₂ with one electron less but with the same crystal structure exhibits a metallic conductivity. MoSi₂, also with the same structure (below about 650°C), and the same electronic configuration as CrSi₂ is a compensated metal. In order to investigate the transition from one type of behaviour to the others we have prepared Cr_xV_1−x and Cr_xMo_1−x alloys deposited by coevaporation of the metals on Si wafers. All the layers which have been treated at 650°C exhibit only one type of diffraction peaks corresponding to a hexagonal C40 solid solution. Hall effect and resistivity measurements indicate that the addition of VSi₂ to CrSi₂ rapidly increases the hole concentration with a clear metallic behaviour at 25 mol% VSi₂. Addition of MoSi₂ produces more gradual changes. Infrared absorption spectra exhibit a clear cutoff around 0.4–0.5 eV depending on the alloy composition.