2007 NSTI Nanotechnology Conference and Trade Show - Nanotech 2007 - 10th Annual

Ab initio calculation of tunneling current through ultra-thin SiO2 gate dielectric of MOS Structure, including the influence of oxygen vacancies on the tunneling current

E. Nadimi, R. Janisch and C. Radehaus
TU Chemnitz, DE

Keywords:
DFT, NEGF, tunneling current, MOS

Abstract:
We used a first-principle atomistic scale method, based on density functional theory and non-equilibrium Green’s function to study the electron tunneling current through ultra thin silicon oxide films. The Si/SiO2 model interface has been constructed by orienting a crystalline SiO2 ??cristobalite slab such that the misfit with Si (001) was minimized. Starting with the geometric construct, all translational and ionic degrees of freedom of the interface system were relaxed. The resulting structure contained no dangling bonds and thus no defect induced gap states were visible in the electronic structure. The calculated work of separation showed that our model interface was energetically favorable. The thin silicon oxide film was then sandwiched between two highly Phosphor-doped silicon contacts. The metallic character of the highly doped contacts allowed the use of comparatively small supercells due to the short screening length. With this model system the influence of single neutral bulk and interfacial oxygen vacancies on the tunneling current was investigated. The study was extended to the presence of two correlated oxygen vacancies, and the influence of vacancies’ position on the correlation energy and tunneling current was investigated. Our results show a striking relationship between the defect’s location and tunneling current.

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