Peculiar properties microstructure in H:LiNbO3 waveguide layers

The structural defects had been found on the surface of high-doped H:LiNbO3 waveguide layers produced on X-cut LiNbO3 substrates in pure benzoic acid at T ≥ 185°C during t>1 h. The defects are similar to "scratches" but oriented definitely in reference to Z crystal axis. Measured 3D and 2D profiles show the defects outspreading above the substrate surface at a height ~4.4-9.0 nm, having width a half height ~1.7 μm and length from ~2 μm up to 100-300 rim. Areas, where the density of these defects is increased, as a rule, are limited by scratch traces from lapping and polishing. Preliminary annealing of the substrates or Ti in-diffusion at temperature ~1000 °C before PE avoid the defect formation and the substrate roughness is not changed by proton exchange.