Peculiar properties microstructure in H:LiNbO3 waveguides 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 degrees 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 similar to 4.4 - 9.0 nm, having width a half height similar to 1.7 mu m and length from -2 mu m up to 100 - 300 mu m. 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 similar to 1000 square C before PE avoid the defect formation and the substrate roughness is not changed by proton exchange.