Understanding the Clean Interface Between Covalent Si and Ionic Al2O3

The atomic and electronic structures of the $(001)\mathrm{\text{\ensuremath{-}}}\mathrm{Si}/(001)\mathrm{\text{\ensuremath{-}}}\ensuremath{\gamma}\mathrm{\text{\ensuremath{-}}}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ heterointerface are investigated by first principles total energy calculations combined with a newly developed ``modified basin-hopping'' method. It is found that all interface Si atoms are fourfold coordinated due to the formation of Si-O and unexpected covalent Si-Al bonds in the new abrupt interface model. And the interface has perfect electronic properties in that the unpassivated interface has a large LDA band gap and no gap levels. These results show that it is possible to have clean semiconductor-oxide interfaces.