Localized Vibrational Modes of Interstitial Oxygen in Si_xGe_1-xAlloys

Abstract

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