Vibrational dynamics of isolated hydrogen in germanium

Absorption line shapes associated with the stretch mode of bond-center hydrogen (formula presented) at (formula presented) and the twofold degenerate mode of hydrogen near the tetrahedral site (formula presented) at (formula presented) in germanium are measured with infrared-absorption spectroscopy. The (formula presented) line shape measured at 10 K for the case of low hydrogen concentrations gives a lifetime between 15 and 23 ps. Similar in magnitude to the (formula presented) observed for the same defect in silicon [M. Budde et al, Phys. Rev. Lett. (formula presented) 1452 (2000)], this observation indicates that the lifetime of the bond-centered mode is largely insensitive to the phonon frequency distributions of the host material. Pure dephasing dynamics of hydrogen in germanium are studied by measuring the shape of the 1794- and (formula presented) lines as a function of temperature. These measurements are analyzed using a recently formulated exchange model for vibrational dephasing. The temperature dependence of the (formula presented) line shape is attributed to thermal fluctuations in the occupation number of a pseudolocalized mode at (formula presented).