Infrared vibrations of interstitial oxygen in silicon-rich SiGe alloys

We report on the infrared spectra of the antisymmetric stretching vibration of OiOi in Si-rich Si1-xGexSi1-xGex alloys. The shift of its frequency is obtained as a function of the germanium content x   below ∼0.5∼0.5. We present a decomposition of the low-temperature spectra using Gauss–Lorentz profiles. A low-lying broad band is found for x=0.08x=0.08, and assigned tentatively to the vibrations of Si2OSi2O units with the nearest sites occupied by several Ge atoms. We compare our experimental findings with results of a recent ab initio study of the phonon modes.