Electronic structure ofCrSi2and related refractory disilicides

The results of linear augmented-plane-wave band calculations for hexagonal ${\mathrm{CrSi}}_2$, carried out in the local-density approximation, confirm that this compound is an indirect-gap semiconductor. The calculated indirect gap of 0.30 eV, which occurs within the Cr 3d band manifold, is in excellent agreement with the measured optical value, 0.35 eV. However, the calculated onset energy for direct transitions (which are predicted to be polarization dependent) is about 0.2 eV below the observed (∼0.67 eV) value. The corresponding calculated indirect gaps for the metastable hexagonal ${\mathrm{MoSi}}_2$ (+0.02 eV) and ${\mathrm{WSi}}_2$ (-0.03 eV) phases are diminished by chemically induced changes in the width and position of the d bands relative to ${\mathit{E}}_{\mathit{F}}$. Similar effects produce a reduced (∼0.22 eV) gap above ${\mathit{E}}_{\mathit{F}}$ for the isostructural group-V compound ${\mathrm{VSi}}_2$. The transmission characteristics of a ${\mathrm{CrSi}}_2$(0001)/Si(111) interface are analyzed in terms of the projected bulk ${\mathrm{CrSi}}_2$ band-structure results.