Electronic structure of theCaF2/Si(111) interface

The electronic structure of the ${\mathrm{CaF}}_2$/Si(111) interface calculated within the local-density-functional theory with the linear muffin-tin orbitals method is presented. We examine the interface states for three different structural models of the Ca-terminated interface. For each model a pair of two-dimensional interface bands is found. The unoccupied interface band around the zone center is a truly localized band while the occupied interface band is buried below the valence-band maximum in agreement with recent experimental results. The nature of the two-dimensional interface states and the extent of localization of the wave functions at the interface are also discussed.