BaTiO₃ waveguides on MgO buffered-sapphire single crystals

Within our program to develop ferroelectric thin film optical waveguides, we have studied the growth of epitaxial waveguides BaTiO₃ on r-plane sapphire substrates with a MgO buffer layer. The films were prepared by pulsed laser deposition (PLD). Their structural properties were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), Rutherford backscattering (RBS) in random and channeling (RBS-c) configuration and atomic force microscopy (AFM). They displayed good crystalline quality, characterized by an RBS-c minimum yield of about 4-6%, a full width at half maximum (FWHM) of the XRD rocking curve measurement of the BaTiO₃(200) reflection of 0.32° and arms roughness of 1.2 nm in a film of approximately 1.0 μm thickness. The epitaxial relationship was found to be BaTiO₃(100)∥MgO(100)∥Al₂O₃(1102). The refractive index, the birefringence and the optical losses have been measured.