Theory of the electronic structure of the Si-SiO2interface

A theory of the Si-Si${\mathrm{O}}_2$ interface based on recent experimental findings for silicon surfaces and their oxidation is presented. It is proposed that a simple local-orbital picture can simultaneously describe silicon, its oxidation, and the Si-Si${\mathrm{O}}_2$ interface and that two dimensionality is not essential to physically meaningful calculations of interface local densities of states. Calculations are performed which show that interface states do not arise simply from the presence of a boundary. It is argued that band tailing at the interface, like that in amorphous silicon, is due primarily to strain rather than to charged centers, and that dangling bonds at the interface should give rise to an inhomogeneously broadened discrete level at midgap.