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The energy levels of the oxygen vacancy in and -Al 2 O 3 were calculated using the screened exchange hybrid functional, and explain the electron hopping and trapping levels seen in deposited Al 2 O 3 at 1.8 eV below its conduction band edge. The vacancy supports five accessible charge states, from 2+ to 2. Electron hopping corresponds to the 0/ level, which lies 1.8 eV below the conduction band edge in -Al 2 O 3 . This level lies much deeper than it does HfO 2 . The + / 0 level lies at 2.8 eV above oxide valence band in -Al 2 O 3 and thus below the Si valence band top.
Liu et al. (Mon,) studied this question.