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

It was recently discovered that in electron-irradiated germanium doped with oxygen a local vibrational mode occurs at 669 cm⁻¹ that could be ascribed to the negatively charged oxygen-vacancy complex (VO⁻). In the 669 cm⁻¹ band and in another unassigned band at 731 cm⁻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 cm⁻¹) infrared measurements at liquid helium temperature of bands at 635,669,716,and 731 cm⁻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 Ge−O−Ge quasimolecule embedded in the germanium lattice. Electron paramagnetic resonance measurements have also been performed on an O doped ⁷⁴Ge 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 VO⁻ center. Through annealing (at 120 °C) a correlation can be made between the intensity of this electron paramagnetic resonance signal and the infrared band at 669 cm⁻¹, giving explicit support to earlier identifications of these signals as due to VO⁻.