Studies on Ge/CeO₂ thin film system using positron beam and Raman spectroscopy

Abstract

Positron beam and Raman spectroscopic studies are reported on a Ge/CeO₂ thin film system grown on a Si substrate. The variation of the Doppler line shape S-parameter, as a function of positron beam energy, shows a pronounced maximum corresponding to the Ge-region of as-grown film, while no equivalent feature is seen in the sample annealed at 773 K. The Raman spectrum of the as-grown film exhibits a broad band, as opposed to a sharp peak observed for the annealed sample. Based on the correlated evidence from the two measurements, it is concluded that the Ge layer in the as-grown sample is amorphous, containing a large concentration of structural vacancies. Isochronal annealing measurements of the lineshape parameter in the temperature range of 300 to 773 K indicate a rather continuous transformation of amorphous Ge to the crystalline state.