Oxygen vacancy levels and electron transport in Al2O3

The energy levels of the oxygen vacancy in alpha- and theta-Al2O3 were calculated using the screened exchange hybrid functional, and explain the electron hopping and trapping levels seen in deposited Al2O3 at similar to 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 theta-Al2O3. This level lies much deeper than it does HfO2. The +/0 level lies at 2.8 eV above oxide valence band in theta-Al2O3 and thus below the Si valence band top.