Energetics and valence-band offset of theCaF2/Si insulator-on-semiconductor interface

From local-density calculations of total energy and valence-band offset, we examine several models of the interface atomic structure of the ${\mathrm{CaF}}_2$/Si interface. We find that the interface with one interfacial fluorine layer is unstable with respect to dissociation or disproportionation. The interface with two fluorine layers (having only Si-F bonds at the interface) is stable when there is excess fluorine. Interfaces with no fluorine layer (having only Si-Ca bonds at the interface) are stable when there is fluorine deficiency. Comparison of the calculated valence-band offset with the experimental value indicates the molecular-beam-epitaxy-grown structure to have only Ca-Si bonds at the interface. We illustrate the potential usefulness of the valence-band offset in the determination of interface atomic structure.