Optical and Structural Characterization of Zn Diffused Lithium Niobate Crystals

One of the most popular and well-established techniques to fabricate low-loss optical waveguides is diffusing of metal ions into Lithium Niobate (LN) crystals. In this work we reported a 3-steps waveguide fabrication process، based on Zn diffusion into LN. First، a layer of Zn with the thickness of 150 nm was sputtered on a hot (127˚C) LN substrate. Then the Zn atoms were oxidized by annealing the sample at 450˚C for 10 min. Finally، thermal diffusion of Zn atoms into LN substrate took place in the different annealing temperatures and times. The aim of this work was to find an optimum diffusing temperature and time of Zn into the LN crystal. Structural and optical characterization of the prepared samples were carried out using XRD، RBS combined with channeling، SEM and double beam spectrophotometer. Our experimental results indicated that almost all of the Zn ions had been diffused into the LN crystal after annealing the sample at 750˚C for 180min. The comparative analyses using XRD، RBS combined with channeling and spectrophotometry، revealed a good stability in optical and crystal structure of LN. Optical transmission and band gap energy of the samples were found to vary with the amount of the Zn content، while in the purchased LN crystal، the band gap was about 4eV، it was dropped to around 2. 9eV after annealing the sample at 800˚C because of diffusing the Zn atoms into the LN crystal. This result promises an improvement on the LN conductivity، therefore an enhancement in its waveguide characteristic.