Optogeometric and waveguiding properties of multimode ZnO planar waveguide sprayed thin films

ZnO thin films with different thicknesses (T1=230.0, T2=450.0, T3=634.0, T4=926.9 and T5=1153.4nm) were deposited by spray pyrolysis on ordinary glass. All of the films had wurtzite crystal structure. The texture coefficient of the (002) plan decreased from 2.74 to 1.64 while that of the (103) increased from 0.65 to 1.23 over the thickness. Flaky shaped grains were observed in the SEM images with a tendency to get larger and hexagonal in shape. The surface evolution was verified by AFM microscopy. The ordinary and extraordinary refractive indices increased with thickness from 1.9344 and 1.9365 to 1.9768 and 1.9830 respectively. The mode order had a significant impact on the confinement of the electric field in the TE mode, therefore the power confinement factor increased by 16.58% with respect to thickness, reaching over 99% whilst it was reduced by 16.39% when the mode order increased from 0 to 4 in T5. •Ordinary and extraordinary refractive indices as a function thickness ZnO waveguide.•Light coupling behavior with thickness.•Mode order and thickness effects on TE electric field and power confinement.•Correlation between the mode order, surface roughness and transmission loss.