The energy levels of the oxygen vacancy in α- and θ-Al2O3 were calculated using the screened exchange hybrid functional, and explain the electron hopping and trapping levels seen in deposited Al2O3 at ∼1.8eV below its conduction band edge. The vacancy supported five accessible charge states, from 2+ to 2−. Electron hopping corresponds to the 0/− level, which lies 1.8eV below the conduction band edge in θ-Al2O3. This level lies much deeper than it did in  HfO2. The +/0 level lies at 2.8eV above oxide valence band in θ-Al2O3 and thus below the Si valence band top.

Oxygen Vacancy Levels and Electron Transport in Al2O3. D.Liu, S.J.Clark, J.Robertson: Applied Physics Letters, 2010, 96[3], 032905