p -type Fermi level pinning at a Si:Al2O3 model interface

To understand the origin of p-type work function shifts in Al2O3-based gate stacks, we constructed two O-rich Si:Al2O3 interface models. A small periodic model is found to be insulating, with no interface states in the Si gap. A larger amorphous Al2O3 interface is found to have its Fermi level pinned in the Si valence band, due to an oxygen deficiency at the interface. This is a mechanism for p-type Fermi level shifts found in gate stacks containing Al2O3 layers.