The structural and chemical details of GeO2∕Ge layers grown on In0.15Ga0.85As substrates by molecular beam deposition were studied in situ by diffraction and spectroscopic techniques. The formation of semiconductor-oxygen bonds at the Ge∕In0.15Ga0.85As interface, which may play a decisive role in dictating the quality of the Ge passivation, was assessed after using two different surface preparations, namely Ar sputtering and atomic hydrogen cleaning.