Control of Heteroepitaxy in Sol-Gel Derived LiNbO₃ Thin Layers

Abstract

Lithium niobate (LiNbO₃) in single crystal form is useful for the fabrication of acoustooptic and active waveguide devices. In this paper, the feasibility of integrating LiNbO₃ thin layers on sapphire is reported. The performance of signal modulators, surface acoustic wave devices, and second harmonic generators relies on control of crystallographic orientation, so a thin-layer deposition method must meet high standards of crystallographic perfection and optical quality. Solution deposition of lithium niobium ethoxide was evaluated on (110) and (006) sapphire substrates for heteroepitaxy. Atomic force microscopy was used to determine the development of microstructure during the transition from the amorphous to crystalline state. Slab waveguides were formed and evaluated for optical quality and loss. Optical losses in the TEo mode of 500nm (110) LiNbO₃ thin layers were determined to be 6 dB/cm. Preliminary results are given for the heteroepitaxial growth of α-Ga₂O₃ buffer layers.