Reflectance anisotropies of polycrystalline Ce_1-x Gd_x O_2-x/2/ Si(001) interfaces

Ce1-xGdxO2-x/2 thin films were deposited by spin coating on oxidized Si(001) substrates. Two strain regimes are observed by mu- Raman spectroscopy: for x < 0.1 the films are tensile strained, whereas a strain component of the wave number shift of -71.2x cm(-1) compensates with a 32.6x cm(-1) bond component for x > 0.1. Reflectance anisotropy spectroscopy (RAS) measurements were carried out on these films in which interface-related optical anisotropies signatures appearing in the 1.5 eV to 3.6 eV photon energy range are found dependent on the incorporation of Gd in the lattice. To explain the observed RAS signatures with a complex reflectance three-phase model, we resorted to spectroscopic ellipsometry (SE) to retrieve the interface optical anisotropies (IOA) related to the changes in refractive index, < Delta n >, between interface formed by both the oxidized Si(001) and polycrystalline CeO2:Gd films, and to assess the CeO2 energy gap variation from 3.2 to 2.8 eV in the 0 < x < 0.4 composition range. This study renders the combination of RAS, Raman, and SE versatile tools to optimize the growth parameters during the fabrication of devices based on polycrystalline CeO2 on a quantitative basis.