We present first-principles calculations of the structural and electronic properties of Si(001)-${\mathrm{SiO}}_2$ interfaces. We first arrive at reasonable structures for the c-$\mathrm{Si}/a-{\mathrm{SiO}}_2$ interface via a Monte Carlo simulated annealing applied to an empirical interatomic potential, and then relax these structures using first-principles calculations within the framework of the density-functional theory. We find a transition region at the interface, having a thickness on the order of 20 Å, in which there is some oxygen deficiency and a corresponding presence of suboxide Si species (mostly ${\mathrm{Si}}^{+2\mathrm{}}$ and ${\mathrm{Si}}^{+3\mathrm{}})$. Distributions of bond lengths and bond angles, and the nature of the electronic states at the interface, are investigated and discussed. The behavior of atomic oxygen in a-${\mathrm{SiO}}_2$ is also investigated. The peroxyl linkage configuration is found to be lower in energy than interstitial or threefold configurations. Based on these results, we suggest a possible mechanism for oxygen diffusion in a-${\mathrm{SiO}}_2$ that may be relevant to the oxidation process.

• Received 28 October 1998

DOI:https://doi.org/10.1103/PhysRevB.59.10132