Effects of electron-electron correlations on defect and interface states in amorphous Si andSiO2systems

The effects of electron-electron correlations are included in the nearest-neighbor tight-binding model of tetrahedrally coordinated covalent solids in the amorphous phase. The amorphous systems are represented by Bethe lattices and the electron-electron interactions are parametrized for a short-range interaction in a Hubbard-like Hamiltonian. Self-consistent solutions are obtained in the Hartree-Fock approximation. If defects are included the self-consistent energy parameters vary with distance away from the defect but the solution is still possible if this variation falls away rapidly over a few shells. The cases of dangling bonds in Si and ${\mathrm{SiO}}_2$ are considered by terminating the Bethe lattice. The former shows localized states in the gap for two charge configurations, but ${\mathrm{SiO}}_2$ shows only one. The interface between Si and ${\mathrm{SiO}}_2$ is represented by joining two Bethe lattices. The self-consistent solution shows appreciable charge transfer on to the first O atom and consequential changes in the local density of states.