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We report infrared absorption spectra of crystalline Si xGe1-x alloys with silicon content 0 < x < 1 at room and liquid nitrogen temperature. We covered the spectral range from 375 to 1200 cm -1 that includes the "Si-Ge" and "Si-Si" single-phonon transitions, the continuum of two-phonon processes, and the localized mode of interstitial oxygen. We study the change of vibrational structure and correlation between reference (pure Si and Ge) and alloy spectra. We observed shifts to lower wave numbers by about 1 cm -1 of the two-phonon absorption bands per 1% increase in germanium concentration. Pronounced changes of the vibrational spectra upon lowering the temperature were detected. The Six Ge1 -x alloys rank among the most interesting solid solutions. They represent a continuous series of crystalline materials with gradually varying properties. Vibrational states of the SiGe 1 -x alloys have been studied several times by infrared methods [1][2][3].In this paper, we present infrared absorption spectra of bulk Si x Ge1-x alloy for 0 < x < 1 in the spectral range 375-1200 cm -1 . As far as we know, it is for the first time that the local vibrations of the interstitial oxygen in the alloys are reported. The measurements have been performed on crystalline and polycrystalline samples grown by Czochralski method. The series of 19 samples covered the whole compositional range from Si to Ge, being mostly polycrystalline. Transmittance spectra have been measured with a FTIR spectrometer Bruker IFS55, the spectral resolution was 1 cm -1 and a number of scans was typically about 100. The transmission Τ of an optically thick slab of thickness d is [4] where K = 4πνk is the absorption coefficient and R = [(n -1) is the reflectivity of a semi-infinite sample with complex refractive index n+ik; n is the real part of the refractive index and k is the extinction coefficient. The approximations are valid for n » k. The real part of the refractive index of the Si x Ge 1 -x alloy has been computed by (899)

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We study infrared-active vibrations of interstitial oxygen in Czochralski-grown samples of Si Gei -x alloys with the silicon content from 0 to 1 between room and liquid nitrogen temperature. The measurements were performed on a large series of samples including single crystals of Si and Si-rich alloys, and polycrystalline samples of alloys with a higher Ge content. We focus on quantitative data on the compositional and temperature evolution of the strongest absorption band above 1100 cm -1 , related to the asymmetric stretching of the Si 2 O pseudomolecule. We have also observed a pronounced Fano-like resonance centered at 520 cm -1 .PACS numbers: 78.30. Am, 63.20.Ρw In Czochralski-grown silicon, germanium, and Si xGe1-x alloy crystals, oxygen exists primarily as an interstitial defect (Oi). The infrared-active vibrations of Οi in Si and Ge have been studied many times. Recently, the structure, dynamics and infrared polarizability have been revised for both Si:O and Ge:O, see Refs. [1][2][3] and references therein.In this paper, we report the basic characteristics of the most prominent Οi absorption bands in the alloys. The results are obtained from a comprehensive set of measurements on 19 samples, covering the whole compositional range from pure Si to pure Ge, performed in the temperature range of 85-300 K. Our main aim is to provide quantitative data on the compositional and temperature evolution of the strongest, localized-vibration band related to the asymmetric stretching of the Si2O pseudomolecule. This band is located at cα. 1106 cm -1 in Si at room temperature, and is known to exhibit a composite structure at low temperatures [4][5][6]. We also report on the structure related to the lower-frequency infrared-active mode, occurring at about 520 cm -1 in pure Si.The measurements have been performed on single-crystal and polycrystalline samples grown by Czochralski (CZ) method. The samples were not intentionally doped; the free-hole concentration at room temperature was typically cα. 10 15 cm-3 . The oxygen concentration was about 10 18 cm-3 throughout the