Temperature dependence of Raman scattering in Ge1-xSix alloys.

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First-order Raman scattering of polycrystalline ${\mathrm{Ge}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Si}}_{\mathit{x}}$ alloys is studied from T=300--900 K. The Raman shifts of the three optical phonons are modeled by considering thermal expansion and coupling to two phonons. The shift of the Si-Si mode near 500 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ has a temperature dependence similar to that of c-Si for x>0.7, but has a slower temperature variation for more Ge-rich alloys. The Ge-Ge mode near 300 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ has a temperature dependence similar to that of the optical-phonon mode in c-Ge for all compositions studied. The Raman shift of the Ge-Si mode has a dependence in between that of the Ge-Ge and Si-Si modes. Also, the Raman linewidths of the Si-Si and Ge-Ge modes have a temperature dependence similar to that of c-Si and c-Ge, respectively.