LIQUID-PHASE EPITAXIAL-GROWTH OF LINBO3 THIN-FILM USING LI2O-B2O3 FLUX SYSTEM

LiNbO3 thin film optical waveguides were fabricated by liquid phase epitaxy. In order to improve the crystallinity and optical transparency of the film, a 5 mol% MgO-doped LiNbO3 substrate and Li2O-B2O3 flux system were used instead of a conventional combination of LiTaO3 Substrate and Li2O-V2O5 flux system. Dependence of film properties on the melt composition was investigated in detail. As a result, high crystallinity with a small linewidth of 11.4 arc sec in the X-ray rocking curve, and good surface morphology with perfect mirror surface were realized by choosing a suitable melt composition. The chemical composition of the grown film was estimated to be nearly stoichiometric from results of several characterizations, and the Li/Nb ratio of the film could not be widely changed by changing the Li2O/Nb2O5 ratio in the melt. The as-grown film shows a perfect transparency for the wavelength down to the fundamental absorption edge resulting in a small guided optical wave propagation loss of less than 1 dB/cm at a wavelength of 458 nm. Ferroelectric domain inversion phenomena at the film-substrate interface, and preliminary results of trial on controlling film properties by Mg, Zn, Na and Ti doping are also shown and discussed.