Charge state of the O$_{2}$ molecule during silicon oxidation through hybrid functional calculations

TL;DR

This study uses hybrid functional calculations to determine the charge state of O$_2$ during silicon oxidation, revealing it remains neutral while diffusing through SiO$_2$ due to the position of charge transition levels.

Contribution

The paper introduces a hybrid functional approach to accurately determine the charge transition levels of O$_2$ in silicon dioxide, clarifying its charge state during oxidation.

Findings

O$_2$ diffuses in a neutral charge state in SiO$_2$

Charge transition level $ ightarrow$ 1.1 eV above Si conduction band edge

Interfacial effects lower the charge transition level

Abstract

We study the charge state of the diffusing O$_2$ molecule during silicon oxidation through hybrid functional calculations. We calculate charge transition levels of O$_2$ in bulk SiO$_2$ 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 $\epsilon^{0/-}$ in bulk SiO$_2$ occurs at $\sim$1.1 eV above the silicon conduction band edge, implying that the O$_2$ 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.