High-resolution local vibrational mode spectroscopy and electron paramagnetic resonance study of the oxygen-vacancy complex in irradiated germanium

Abstract

It was recently discovered that in electron-irradiated germanium doped with oxygen a local vibrational mode occurs at $669\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ that could be ascribed to the negatively charged oxygen-vacancy complex $({\mathrm{VO}}^{\ensuremath{-}})$. In the $669\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ band and in another unassigned band at $731\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ due to a different defect, fine structures indicating the occurrence of a germanium isotope splitting of the modes could be partly resolved. We report here the results of high-resolution $(=0.02\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1})$ infrared measurements at liquid helium temperature of bands at $635,669,716,\mathrm{and}\phantom{\rule{0.3em}{0ex}}731\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. In this work, the experimentally observed splitting of all four local vibrational modes and the amplitudes of the individual components within each mode are accurately predicted from a nonlinear symmetric $\mathrm{Ge}\ensuremath{-}\mathrm{O}\ensuremath{-}\mathrm{Ge}$ quasimolecule embedded in the germanium lattice. Electron paramagnetic resonance measurements have also been performed on an $\mathrm{O}$ doped $^{74}\mathrm{Ge}$ quasi monoisotopic sample after electron irradiation. The symmetry of the dominant paramagnetic defect in the sample is found to be orthorhombic I and the principal $g$ values are in good agreement with those reported earlier for the ${\mathrm{VO}}^{\ensuremath{-}}$ center. Through annealing (at $120\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$) a correlation can be made between the intensity of this electron paramagnetic resonance signal and the infrared band at $669\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, giving explicit support to earlier identifications of these signals as due to ${\mathrm{VO}}^{\ensuremath{-}}$.