Reactions of hydrogen with Si-SiO2 interfaces

Radiation experiments have established that H+ released in SiO2 migrates to the Si-SiO2 interface where it can induce new defects. For oxides exposed first to high-temperature annealing and then to molecular hydrogen, mobile positive charge believed to be H+ can be cycled to and from the interface b y reversing the oxide electric field. We report first-principles calculatio ns that identify atomic-scale mechanisms for the two types of behavior and the conditions that are necessary for each. Si-Si bonds an the oxide side, i.e., "suboxide bonds," can trap H+ in deep wells with an asymmetric barrie r (1.5 eV on the Si side, 1 eV on the SiO2 side). In radiation experiments these centers can act as fixed positive charge. In the mobile-positive-char ge experiments, the protons can be cycled between opposing Si-SiO2 interfac es if the density of suboxide bonds is high.