Preparation of epitaxial LiNbO3 films by the sol-gel method

The effect of substrates on the crystallinity and interdiffusion behaviors in sol-gel derived LiNbO₃ films were investigated using X-ray diffraction, transmission electron microscopy and secondary ion mass spectroscopy. The epitaxial films were obtained on (0001)-sapphire, (0001)-LiTaO₃ and (0001)-5%MgO doped LiNbO ₃ substrates with similar crystal structures, but with a variety of lattice constants. When sapphire, which has the largest lattice mismatch with the film, was used, the resulting films heat-treated at 500°C showed a low degree of crystallinity. On the other hand, the films on LiTaO₃ and 5% MgO doped LiNbO₃ , which have smaller lattice mismatches, showed better degrees of crystallinity. Furthermore, these epitaxial films were formed without serious interdiffusion. Our study shows LiNbO₃ films, for the practical application such as optical waveguides, can be prepared by the sol-gel method using a substrate with a small lattice mismatch