SO4* complex in CdTe: Infrared absorption spectroscopy and first-principles calculations

A sulfur-oxygen complex in CdTe characterized by IR absorption lines at 1097 and $1108 {\mathrm{cm}}^{\ensuremath{-}1}$ is studied by means of infrared absorption spectroscopy and first principles theory. Temperature-sensitive measurements performed on samples with different $¹⁶\mathrm{O}:¹⁸\mathrm{O}$ isotope ratios show that these lines are due to a split ${\ensuremath{\nu}}₃$ stretch vibrational mode of a disturbed sulfate ion $({\mathrm{SO}}₄^{2\ensuremath{-}})$ transformed under the ${A}₁$ $(1097 {\mathrm{cm}}^{\ensuremath{-}1})$ and $E$ $(1108 {\mathrm{cm}}^{\ensuremath{-}1})$ representations of the ${C}_3v$ point group. The ${\ensuremath{\nu}}₁$ symmetric stretch, ${\ensuremath{\nu}}₄$ bend, and ${\ensuremath{\nu}}₁+{\ensuremath{\nu}}₃$ combination modes of the ion are also identified. An axially disturbed ${\mathrm{SO}}₄$ located at the Cd vacancy site is proposed as a microscopic model of the complex.