Semiconducting transition metal silicides: electronic structure, electrical and thermoelectrical properties

The actual knowledge existing on electronic structure determinations for semiconducting transition metal silicides obtained from band structure calculations and investigations of optical interband spectra is reviewed. The emphasis is put on the information available for the semiconducting 3d transition metal silicides which is combined with recently gained experimental and theoretical data for the semiconducting 4d and 5d transition metal silicides. From band structure studies and optical investigations it is concluded that most semiconducting transition metal silicides are indirect-gap materials. An electrical data analysis indicates that all non-intentionally doped semiconducting silicides exhibit hole conduction with relatively high carrier concentrations even in epitaxial films and single crystals. The experimental electron to hole mobility ratios are less than unity, i.e. mobilities of electrons are usually much lower than those of holes. Effective masses seem to be /spl ges/1 free electron mass for most semiconducting silicides. The extensive work done on the electrical and thermoelectrical properties of semiconducting iron disilicide thin films and single crystals is considered in more detail.