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 rapid- ly over a few shells. The cases of dangling bonds in Si and Si02 are considered by terminating the Bethe lattice. The former shows localized states in the gap for two charge configurations, but Si02 shows only one. The interface between Si and Si02 is represented by joining two Bethe lattices. The self-consistent solution shows appreciable charge transfer on to the first 0 atom and consequential changes in the local density of states.