Structure, electronic properties, and energetics of oxygen vacancies in varying concentrations of SixGe1-xO2

Abstract

SiGe alloys, widely used in various technological applications, are typically interfaced with a thermally grown oxide layer that is composed of SixGe1-xO2, a composite material which is also used for technological applications in its own right. Point defects in this oxide layer influence the electronic and structural properties, which can detrimentally affect the desired application. In this paper, we use ab initio calculations to investigate the canonical oxygen vacancy in systems of varying compositions of SixGe1-xO2. We find that the electronic structures and geometries of the vacancies remain qualitatively similar to their well-known analogs in SiO2 and GeO2 regardless of the composition and similar to previous results in the literature on Ge-doped SiO2. They show a wide distribution of formation energies and one-electron levels across the various concentrations of SixGe1-xO2. However, our results show that the factor defining their quantitative behavior is not the con-centration, rather it is the chemistry of the atoms around the vacancy, each combination of which has its own distribution of properties. The resulting charge transition levels similarly cover a wide range of the band gap. These results aid the understanding of reliability issues in technological applications.