Isotopic shifts of the low-energy excitations of interstitial oxygen in germanium

The rotational states of O-i in natural Ge as determined by phonon spectros copy are found to be shifted in isotopically enriched Ge:O-i crystals. Thes e shifts are larger than compatible with the line width in natural Ge if on ly the motion of the quasi-free Ge-O-Ge molecule is considered. Because of the reduced isotope scattering of the phonons in the enriched Ge the positi on of higher excited states could be determined. This allows to estimate th e height of the axial potential barrier by extending to Ge:O the Yamada-Kan eta model for Si:O. (C) 1999 Elsevier Science B.V. All rights reserved.