Lithium niobate thin film growth using solid source metal-organic chemical vapor deposition for waveguiding applications

Thin film lithium niobate (LiNbO{dollar}sb3){dollar} hetero-structural waveguides offer several advantages over currently used bulk devices including a tight beam confinement due to a large optical index difference between guiding and cladding layers. However devices superior to bulk devices have not yet been prepared. The challenge is to grow and process a waveguide device structure with very low optical losses.; In this research program, high quality thin films of LiNbO{dollar}sb3{dollar} were deposited by the solid-source MOCVD method on sapphire, lithium tantalate (LiTaO{dollar}sb3){dollar} and SiO{dollar}sb2{dollar} coated Si substrates. This method is capable of producing high quality oxide films with precise control of the stoichiometry, especially in multi-cation systems.; In case of the epitaxial growth of LiNbO{dollar}sb3{dollar} on sapphire and LiTaO{dollar}sb3{dollar} substrates, the effect of growth conditions on film quality and optical properties were thoroughly studied. It was found that grain orientation, size, and surface roughness could be controlled by choosing appropriate deposition conditions.; Since scattering from rough film surfaces is the major source of optical attenuation, a knowledge of the mechanisms involved in film roughening is essential. In this study, it was found that roughening in LN films grown on sapphire increased with grain size and the depth of the grain boundary grooves. By increasing the nucleation density during the initial stage of film growth, it was possible to inhibit grain growth, thereby reducing the surface roughness. Based on these studies, a 2-step growth process was developed. This process involved (1) creating a high nucleation density during the early stages of film growth, and (2) enhancing the crystallinity by growing the balance of the film at higher temperatures. Using this growth process, LN films became smoother while maintaining the same crystalline quality with conventional one step grown films. As a result, optical losses were reduced to below 1.8 dB/cm for the TE{dollar}rmsb{lcub}o{rcub}{dollar}, mode at a wavelength of 632.8 nm.; The crystallinity and optical properties of LN films deposited on SiO{dollar}sb2{dollar}/Si substrates were also investigated, and highly (006) textured films with good optical quality (optical losses {dollar}<{dollar}5 dB/cm) were obtained for the first time without the application of an electric field.