Formation and dissociation reactions of complexes involving interstitial carbon and oxygen defects in silicon

Abstract

We present a detailed first-principles study which explores the configurational space along the relevant reactions and migration paths involving the formation and dissociation of interstitial carbon-oxygen complexes, ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{\mathrm{i}}$ and ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{2i}$, in silicon. The formation/dissociation mechanisms of ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{\mathrm{i}}$ and ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{2i}$ are found as occurring via capture/emission of mobile ${\mathrm{C}}_{\mathrm{i}}$ impurities by/from O-complexes anchored to the lattice. The lowest activation energies for dissociation of ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{\mathrm{i}}$ and ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{2i}$ into smaller moieties are 2.3 eV and 3.1 eV, respectively. The first is compatible with the observed annealing temperature of ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{\mathrm{i}}$ , which occurs at around 400 ${}^{\circ }$C, and below the threshold for ${\mathrm{O}}_{\mathrm{i}}$ diffusion. The latter exceeds significantly the measured activation energy for the annealing of ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{2i}$ ($E_{\mathrm{a}}=2.55$ eV). We propose that instead of dissociation, the actual annealing mechanism involves the capture of interstitial oxygen by ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{2i}$, thus being governed by the migration barrier of ${\mathrm{O}}_{\mathrm{i}}$ ($E_{\mathrm{m}}=2.53$ eV). The study is also accompanied by measurements of hole capture cross sections and capture barriers of ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{\mathrm{i}}$ and ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{2i}$. In combination with previously reported data, we find thermodynamic donor transitions which are directly comparable to the first-principles results. The two levels exhibit close features, conforming to a model where the electronic character of ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{2i}$ can be described by that of ${\mathrm{C}}_{\mathrm{i}}{\mathrm{O}}_{\mathrm{i}}$ perturbed by a nearby O atom.

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• Can we rely on hybrid-DFT energies of solid-state problems with local-DFT geometries?