Influence of defects on elastic gate tunneling currents through ultrathin SiO₂ gate oxides: predictions from microscopic models

We study theoretically the influence of neutral oxygen vacancies on the magnitude of elastic tunneling currents through the ultrathin (1.3 nm) gate oxide of a prototypical metal-oxide field-effect transistor with a channel length of 50 nm. For the calculation of the gate currents, we have used transmission coefficients obtained from three-dimensional semiempirical tight-binding calculations for a model Si-SiO₂-Si junction, and electron distribution functions based on full-band Monte-Carlo transport simulations. The positions of the atoms in the junction were determined by first-principles density-functional calculations. It is found that the gate currents increase significantly (by typically one to three orders of magnitude) in the presence of vacancies having a density around 10¹² cm^-2, provided that the resonant energy levels lie less than 1 eV above the Si conduction band edge.