Semiempirical electronic-structure calculations of the hydrogen-phosphorus pair in silicon

We report the results of electronic-structure calculations on the hydrogen-phosphorus pair in silicon using the modified neglect of diatomic differential overlap (MNDO) method with a finite cluster. We find that the stable geometry for the defect has ${\mathit{C}}_{3\mathit{v}}$ point-group symmetry with the hydrogen located at the antibonding position of the silicon, which is, in turn, adjacent to the substitutional phosphorus. This prediction is consistent with a model inferred on the basis of infrared spectroscopy. We also calculate hydrogen vibrational frequencies of 2140 and 630 ${\mathrm{cm}}^{\mathrm{-}1}$, respectively, for the axial and perpendicular motions. These are considerably different than the values of 1555 and 809 ${\mathrm{cm}}^{\mathrm{-}1}$, assigned on the basis of infrared experiments. The physical characteristics of the defect and these differences are discussed.