Structural and optical properties of epitaxial Ca_xBa_1-xNb₂O₆ thin films grown on MgO by pulsed laser deposition

In the present work, we investigate in detail the effect of both the deposition temperature and the cooling rate on the growth of calcium barium niobate (CBN) thin films on a magnesium oxide (MgO) single crystal substrate. As revealed by x-ray diffraction measurements, epitaxy occurs for films deposited at 800 °C with a slow in situ cooling rate. We have also investigated the chemical composition of the films by way of a Rutherford backscattering spectroscopy technique and of an elastic recoil detection analysis, which reveal a good stoichiometry for our samples. In addition, optical analysis (UV-visible spectroscopy and spectroscopic ellipsometry) is performed on both polycrystalline and epitaxial films. A high transmittance (≫85%) and a refractive index close to that observed for bulk crystal are obtained for epitaxial CBN films deposited at a low oxygen pressure. X-ray reflectivity measurements have enabled us to correlate the density of the films with their refractive indices.