Germanium thin films have been deposited on GaAs substrates by direct deposition from a 40-eV 76 Ge+ ion beam. The effectiveness of in situ surface treatments and the relationship of deposition temperature to the quality of epitaxy have been examined. Single-crystal, epitaxially oriented Ge layers were grown at temperatures from 270 to 410 °C. Ion channeling measurements on these layers showed excellent minimum yields. Transmission electron microscopy revealed a uniform distribution of small dislocation loops (diameter <10 nm) in the Ge film and a band of buried dislocation loops in the GaAs substrate. The defect characteristics were temperature dependent such that the average loop size in the epitaxial films decreased with temperature but the total damage density increased when the deposition temperature was lower than 410 °C. Formation of these dislocation loops is ascribed to the coalescence of migrating interstitials which originate as low-energy recoils near the growing surface.