Dual behavior of H+ at Si–SiO2 interfaces: Mobility versus trapping

We report first-principles calculations showing that protons in the vicinity of a Si–SiO2 interface can behave in two different ways. At an abrupt interface without suboxide bonds (Si–Si bonds at the oxide side of the interface) H+ does not become trapped but migrates laterally until it reacts with a point defect (e.g., depassivates a hydrogenated dangling bond). On the other hand, when large concentrations of suboxide bonds are present, H+ can become trapped in a deep energy minimum with a highly asymmetric energy barrier. Thus, large H+ densities first saturate suboxide bonds, and the balance can be cycled back and forth between a pair of interfaces by reversing the electric field. These results account for the experimentally observed dual behavior of protons at Si–SiO2 interfaces.