They were found to lie just below the mid-gap in the oxide; equivalent to being

below the Si valence band edge when aligned to the silicon band structure. This

low energy accounted for the behaviour of Al2O3 in oxide capping layers and as an

insulator.

Oxygen Vacancy Levels and Interfaces of Al2O3. D.Liu, J.Robertson:

Microelectronic Engineering, 2009, 86[7-9], 1668-71