PHONON SPECTROSCOPY OF THE LOW-ENERGY VIBRATIONS OF INTERSTITIAL OXYGEN IN GERMANIUM

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 interstitia l oxygen (O(i)) as a rigid rotator around a [111]-axis slightly pertur bed by the lattice potential. The sequence of transitions can be fit a ssuming a binding angle of (106 +/- 1)degrees which is much smaller th an the value of (162 +/- 1)degrees for O(i) in Si. Line shifts and spl ittings with uniaxial stress along [100], [110], and [111] are in qual itative agreement with this interpretation.