Observation of the Neutral Oxygen Vacancy in Silicon Dioxide

We have studied electron-trapping defects in SiO₂ films incorporated into Metal-Oxide-Silicon capacitors. The film consisted of SiO₂ sputtered onto the native oxide formed on silicon. A process of direct band-to-trap tunneling of electrons into defects within the oxide film was isolated. This trap filling process, and the reverse emptying process, were analyzed using the assumptions that the trapping defects had a fixed spatial location and an extended energy level distribution. For a trap located at the sputtered SiO₂/native SiO₂ interface, we found a trap depth of 4 eV and a trap relaxation of 1 eV upon capture of an electron. These experimental results are consistent with theoretical calculations for the formation of a neutral oxygen vacancy in quartz by the addition of an electron to a positively-charged oxygen vacancy (that is, to an E₁′ center). We therefore may have obtained the first direct experimental evidence for a neutral oxygen vacancy in SiO₂.