Ab initio Calculation of Tunneling Current through Ultra-Thin SiO2 Gate Dielectrics of MOS Structures, Including the Influence of Oxygen Vacancies on the Tunneling Current

Ab initio density functional theory and ballistic transport theory are applied to the calculation of tunneling current through ultra-thin SiO2 gate dielectrics. The Si/SiO2/Si model interface has been constructed by orienting a crystalline SiO2 (β−cristobalite) slab such that the misfit with Si (001) was minimized and no dangling bonds appear at the interface. The structure was then sandwiched between two n-doped Si contacts and tunneling current was calculated using ballistic transport theory. Different oxygen vacancies were created in SiO2 and their influence on the tunneling current was studied. All vacancies result in an increase of tunneling current. However arm vacancies (between a surface Si atom and the first Si layer in bulk SiO2) seem to have the most destructive effect on tunneling current at low biases. Different bulk vacancies show almost equal influence on the tunneling current.