Stable atomic geometries of oxygen microclusters in silicon

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Abstract
Atomic and electronic structures of oxygen-impurity microclusters in crystalline silicon have been explored by a first-principles pseudopotential total-energy cluster calculation within the local-density-functional formalism. The stable atomic geometry of each cluster has been obtained by allowing the atoms in the cluster to relax, according to the calculated forces acting on the atoms, to the total-energy-minimized configuration. It is found that a drastic rearrangement of bond configuration between the oxygen and the silicon atoms occurs in the theoretically determined stable atomic geometry for the three-oxygen-atom cluster in silicon, and that the calculated stabilization energy for the geometry, 3.9 eV per oxygen atom, is comparable with that of the most stable isolated bond-centered interstitial configuration, 4.6 eV. The stability of other atomic configurations is also examined, and a mechanism for the oxygen diffusion process along the bond-centered and the split-interstitial sites is proposed. Bistability between the two stable three-oxygen-atom configurations is found, and its manifestation is briefly discussed.