Germanium oxidation occurs by diffusion of oxygen network interstitials

Density functional modeling is used to show that germanium oxidation occurs by the diffusion of network oxygens across the film as peroxyl bridges, not by molecular O₂ interstitials (O₂*). The smaller O bond angle of GeO₂ leads to lower order rings in the amorphous GeO₂ network than in SiO₂. This leads to narrower interstitial diffusion channels, and less dilation of the interstitial volume around the transition state. This raises the migration barrier of O₂∗ in GeO₂, so that the overall diffusion energy of O₂∗ in GeO₂ is now higher than that of a network O interstitial. The low formation energy of the O vacancy in GeO₂ leads to GeO₂ being O-poor very near the Ge/GeO₂ interface, but the lower overall diffusion energy of the O network interstitial than the vacancy leads to the network interstitial dominating diffusion