Preparation of textured LiNbO3 thin films by off-axis laser deposition and their characterization

We report on the preparation of lithium niobate thin films on (01.2) and (0001) sapphire and LaAlO₃ (01.2) single crystalline substrates using off-axis laser deposition. X-ray diffraction in Bragg-Brentano geometry and in a microdiffractometer with an area detector were used to characterize the crystallography, the texture and the lateral homogeneity of the films. We examined the film morphology with atomic force microscopy (AFM) and scanning electron microscopy (SEM). For the preparation of thin films, the deposition temperature, the deposition pressure and the oxygen-Ar ratio of background pressure were varied. The films grow textured and oriented on the substrates used. For thin films on LaAlO₃ substrates we found only (01.2) reflections of film and substrate in the Bragg-Brentano diffractometer with its selective reflection recording. This suggests that the films are oriented grown and consist of a single LiNbO₃ phase. Investigations with the microdiffractometer showed that there is also an amount of a LiNb₃O₈ textured phase in the films. Thin films deposited on sapphire substrates consist of different mixtures of the LiNbO₃ phase and the LiNb₃O₈ phase depending on the oxygen-Ar ratio of ambient atmosphere. At an oxygen-Ar ratio of 1:4, the films consist mainly of oriented LiNbO₃. The dielectric polarization and domain structure of the films were investigated by electric scanning force microscopy