Highly reflective Er-doped ZnO thin-film coating for application in a UV optical ring resonator

We achieved doping-induced optical variation in Erbium-doped ZnO (EZO) that may prove to be a promising material for use in optical ring resonators. EZO thin-film samples were deposited on n-type Si substrate via the sol-gel spin-coating technique followed by annealing in air at 500 °C. The doping-induced morphological variations of the deposited thin film were characterized using x-ray diffraction, ellipsometry, scanning electron microscopy and energy dispersive x-ray spectroscopy. Further, in order to establish the suitability of EZO for optical applications, detailed optical analysis was performed that exhibited that 1 mol% Er-doped ZnO may prove to be suitable material. Finally, a ring resonator design has been proposed using 1 mol% EZO thin film. The proposed structure was simulated using the MODE tool by Lumerical solutions. The Eigenmode Solver has been used to simulate and calculate the effective refractive index, group velocity, propagation constant β, dispersion and bending losses for a wavelength region of 200 nm to 900 nm. Simplified expressions for the free spectral range, full-width at half-maximum and quality factor have been derived and validated by the simulated data for the proposed ring resonator.