Phonon spectroscopy of the low energy vibrations of interstitial oxygen in germanium

Abstract

In oxygen doped Ge we find by phonon spectroscopy with superconducting tunnelling junctions a series of lines between 0.18 meV and 4.08 meV which can be interpreted as due to low lying states of the interstitial oxygen (Oi) as a rigid rotator around a <111>-axis slightly perturbed by the lattice potential. The sequence of transitions can be fit assuming a binding angle of (106 ± 1)° which is much smaller than the value of (162 ± 1)° for Oi in Si. Line shifts and splittings with uniaxial stress along <100>, <110> and <111> are in qualitative agreement with this interpretation.