Charge state of the O2 molecule during silicon oxidation through hybrid functional calculations
Abstract
We study the charge state of the diffusing O2 molecule during silicon oxidation through hybrid functional calculations. We calculate charge transition levels of O2 in bulk SiO2 and use theoretical band offsets to align these levels with respect to the Si band edges. To overcome the band-gap problem of semilocal density fuctionals, we employ hybrid functionals with both predefined and empirically adjusted mixing coefficients. We find that the charge transition level ε0/- in bulk SiO2 occurs at 1.1 eV above the silicon conduction band edge, implying that the O2 molecule diffuses through the oxide in the neutral charge state. While interfacial effects concur to lower the charge transition level, our estimates suggest that the neutral charge state persists until silicon oxidation.