Strange lifetimes of the vibrations of interstitial oxygen in SiGe alloys

The transient-bleaching decay time of the ν3 (1136 cm−1) band of oxygen in Si1−xGex alloys, at low temperatures, is found to increase rapidly from a few tens of picoseconds when x=0, to 125 ps when x is in the range 0.011–0.066. We show that the increased decay time is caused partly by perturbations of the oxygen by the Ge, and partly by the small decrease in the frequencies of the lattice modes in the alloy. The decay time of ν3 in crystalline germanium (x=1) is also ∼115 ps, similar to that for the dilute alloys, but it is shown to occur through a different three-phonon process.