Electronic Properties of the Si/SiO sub 2 Interface from First Principles

Unoccupied oxygen p-projected densities of states, calculated from first principles in a model Si/SiO sub 2 interface, are found to reproduce recent atomic resolution electron energy-loss spectra (D.A. Muller et al, Nature 399, 758 [1999]). The shape of the unoccupied states and the magnitude of the local energy gap are explicitly related to the number of O second neighbors of a given oxygen atom. The calculated local energy gaps of the oxide become considerably smaller within 0.5 nm of the interface, suggesting that the electronic properties do not change abruptly at the interface.