Electronic structure ofα-alumina and its defect states

Abstract

We have investigated the electronic structure of $\alpha$-alumina and its defect states by using a semiempirical method. Our results show that the fundamental gap is indirect, and the charge transfer enhances the hybridization of aluminum and oxygen orbitals, which in turn leads to the broad upper and lower valence bands. Using the calculated total and orbital density of states, we have provided a consistent interpretation of the existing spectra. For the ideal $\alpha$-${\mathrm{Al}}_2$ ${\mathrm{O}}_3$(0001) surface we have found that the Al—O bonds at the surface have a considerable covalent character and the Al—dangling bonds produce the major surface-state band. Energy positions of the oxygen-vacancy states, and of the surface states, strongly suggest that the oxygen deficiency is responsible for some of the lowenergy structures in the excitation spectra.