Oxygen vacancy with large lattice distortion as an origin of leakage currents in SiO/sub 2/

The origin of electron traps, which induce leakage currents in SiO/sub 2/ films, is predicted to be an oxygen (O) vacancy from first-principles total-energy calculations. Once a neutral O vacancy traps holes, it spontaneously changes to a large distorted structure. The distorted O vacancy can capture electrons, and remains as an electron trap in SiO/sub 2/ films. These results give a microscopic explanation for a trap model that is empirically deduced from experiments. The energy level of the generated electron trap exists near the band offset between the conduction band of SiO/sub 2/ and that of Si. From these results, the electron trap originating from a hole trapped O vacancy can be considered as one origin of the so-called stress-induced leakage currents in SiO/sub 2/ films.