Bond-centered interstitial hydrogen in silicon: Semiempirical electronic-structure calculations

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Abstract
We report the results of electronic-structure calculations on interstitial hydrogen in silicon using the semiempirical modified neglect of diatomic overlap method with a finite cluster. We find that the interstitial hydrogen is stable at a bond-centered site, consistent with other, recent computational results. The barrier for migration between adjacent bond-centered sites is estimated to be ≲1 eV. Furthermore, contrary to most other studies, we find the hydrogen to be asymmetrically located between the near-neighbor silicons. In a static picture, it is therefore bonded in a rather conventional way to one silicon, with the unpaired electron primarily located at the other silicon. However, we find that the barrier for inversion between neighboring silicons (along the bond) is quite small (≲0.1–0.2 eV); hence, motional effects are significant. Possible manifestations of this asymmetry are discussed.