Tunneling properties versus electronic structures in Si/SiO²/Si junctions from first principles

Using first-principles calculations, we study tunneling properties and electronic structures of Si(001)/SiO²/Si(001) junctions in a wide energy range covering the local energy gap in the SiO² regions. We show that the tunneling spectra T(E) as functions of energy E have overall similarity to the projected densities of states (PDOS) at the centers of the SiO² regions, but T(E) and PDOS have significant difference in their dependencies on the SiO² thickness. From the energy dependencies of T(E) and PDOS, distinctive energy ranges are recognized in the valence and conduction bands, reflecting the local electronic structures in the SiO ² region induced from the Si regions. From the difference in the SiO²-thickness dependencies of T(E) and PDOS and from eigenchannel analysis, we find that the tunneling wave function inside the SiO² region decreases with a decay rate which itself decreases as the tunneling distance increases, resulting in a smaller averaged decay rate per length for a thicker SiO² region. These results provide a rich picture for the SiO² barrier in the aspects of tunneling and local electronic structures, and a theoretical framework generally applicable to other tunneling barriers.