Control of Crystallinity in Sol-Gel Derived Epitaxial LiNbO₃ Thin Films on Sapphire

Abstract

Control of crystallinity in solid phase epitaxial growth of LiNbO 3 thin films derived from methoxyethoxide solution on sapphire substrates has been attempted by investigating growth variables. Crystallization at 700° C for longer than 30 min was necessary for full crystallization of LiNbO 3 thin films, although the orientations of the LiNbO 3 crystal planes parallel to the substrates were almost independent of crystallization temperature and crystallization time. Layer-by-layer crystallization and preparation of an ultrathin initial layer have been found to be important in the growth of high-quality epitaxial LiNbO 3 thin films. X-ray diffraction analysis revealed that perfectly single-plane-oriented epitaxial LiNbO 3 thin films, with rocking curve full width at half-maximum of less than 0.07°, were produced on sapphire (001) substrates. Refractive index of 2.24 and optical propagation loss of 3.0 dB/cm were achieved.