First-principles density functional theory and non-perturbative scattering theory were used to investigate the effect of point defects upon ultra-thin oxide films. In particular, O vacancies and B interstitials in monoclinic HfO2 were considered. Five different defects were examined. These were an O vacancy at a 3- or a 4-coordinated O site located in HfO2, an O vacancy along a Hf-O-Si bond or along a Si-O-Si bond at a Si/HfO2 interface, and an interstitial B atom in HfO2. It was found that neutral bulk vacancies or an interface vacancy along the Si-O-Si bond had little effect upon the leakage current. However, an interface vacancy along the Hf-O-Si bridge or an interstitial B atom in HfO2 introduced states into the Si band-gap and in the region just below the Si valence-band edge; thus strongly enhancing the leakage current under low bias.

Difficulties of the Microscopic Theory of Leakage Current through Ultra-Thin Oxide Barriers - Point Defects. L.R.C.Fonseca, A.A.Demkov, A.Knizhnik: Physica Status Solidi B, 2003, 239[1], 48-58