First-principles matrix Green's function calculations were used to study coherent charge-tunnelling through ultra-thin SiO2 layers in metal-oxide-semiconductor devices. The tunnelling behavior was analyzed within the atomistic picture based upon the overlap of Si-induced gap states in the oxide region. It was found that, while interface roughness defects such as sub-oxide bonds and protruding O atoms only weakly affected the tunnelling current, a network of O vacancies composed of Si-Si bonds across the oxide layer drastically increased the gate leakage current due to the defect-assisted tunnelling. It was shown that the formation of such percolation paths was energetically favorable in the non-equilibrium situation, and even the O divacancy was enough to result in dielectric breakdown of ultra-thin oxide layers.

Direct and Defect-Assisted Electron Tunneling Through Ultrathin SiO2 Layers from First Principles. J.Kang, Y.H.Kim, J.Bang, K.J.Chang: Physical Review B, 2008, 77[19], 195321 (5pp)