XPS study of the growth kinetics of thin films obtained by thermal oxidation of germanium substrates

X-ray photoelectron spectroscopy (XPS) has been used to investigate the oxidation of (011) and (001)Ge surfaces. The sample surfaces were CP4 etched then pre-annealed under vacuum at T=600°C or Ar-sputtered before the oxidation. The oxidation treatments have been carried under pure dry oxygen atmosphere and for different durations. The results show that, at the early stages of the oxidation process, the oxide layer contains different oxidation states of germanium. As the oxidation duration increases, the proportions of the high oxidation states (Ge4+ and Ge3+) increase at the expense of those of Ge1+and Ge2+ following first-order kinetics. Very small values of the oxide thickness that were calculated suggest the formation of islands of germanium oxide that cover part of the surface. The argon sputtering prior to the oxidation treatment enhances the growth rate of the oxide film during the first stage of the oxidation process.