Relationship between trapped holes, positive ions, and interface states in irradiated Si-SiO₂ structures

We show that trapped holes at the Si-SiO₂ interface account for all of the interface states generated by gate-positive irradiation of metal-oxide-silicon structures. The field-induced conversion of trapped holes to interface states is found to be the rate-limiting step in interface state buildup. Interface-state generation by hole trapping at the Si-SiO₂ interface also plays a role for gate-negative irradiation. However, our experiments demonstrate an additional avenue for interface-state formation under these conditions. Holes created in the SiO₂ layer are swept to the Al-SiO₂ interface where they release positive ions. The transport of these ions to the Si-SiO₂ interface under gate-positive field results in new interface states. Our data do not support models involving liberation of protons in the bulk of the SiO₂ layer by hole transport through the oxide.