Single crystals were implanted with protons, and the infra-red absorption spectra of the samples were found to contain sharp absorption lines that were due to the excitation of H-related local vibrational modes. Lines in Si (743.1, 748.0, 1986.5, 1989.4/cm) and in Ge (700.3, 705.5, 1881.8, 1883.5/cm) originated from the same defect in the 2 materials. Measurements on samples which were co-implanted with protons and deuterons showed that the defect contained 2 equivalent H atoms. Uniaxial stress measurements were also performed. It was shown that the defect had monoclinic-II symmetry, and the orientations of the Si-H and Ge-H bonds of the defect were determined. First-principles local-density functional theory was used to calculate the structure of the self-interstitial that bound one and two H atoms in Si and Ge; together with the structure of the self-interstitial itself. The observed properties of the defect were in excellent agreement with those calculated for the self-interstitial which bound two H atoms.

M.Budde, B.B.Nielsen, P.Leary, J.Goss, R.Jones, P.R.Briddon, S.Oberg, S.J.Breuer: Physical Review B, 1998, 57[8], 4397-412