Structural Characterizations and Optical Properties of CeO2 Thin Films Prepared by Laser Molecular-Beam Epitaxy

Epitaxial CeO2 thin films were deposited on Si (111) substrates by laser molecular-beam epitaxy (LMBE). Surface roughness, crystalline structure and optical constants were characterized by in situ reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), Raman spectroscopy and spectroscopic ellipsometry. AFM showed that the epitaxial CeO2 film has a quite smooth surface with a root mean square roughness of 0.563 nm over a 2 mu m x 2 mu m area. Raman spectroscopy results indicated good crystallinity of the thin film. Refractive index n and extinction coefficient k of the thin films were calculated in the wavelength region of 370-1000 nm and the values were found to gradually decrease from 2.90 and 0.0321 at 370 nm to 2.35 and 0.0017 at 1000 nm, respectively. The direct and indirect optical band gaps of the film were estimated to be around 3.17 and 2.64 eV, respectively.