Effect of titanium in LiNbO₃ on domain growth during e-beam writing

We report the features of domain growth during e-beam recording on non-polar Y-surfaces of LiNbO 3 crystals doped with titanium at various concentrations ( C Ti ). The nominally pure LiNbO 3 of the congruent composition (CLN), LiNbO 3 doped with 0.5 mol% TiO 2 (CLN-0.5Ti), and the Ti:LiNbO 3 planar waveguide formed as a result of high-temperature diffusion of titanium were comparatively studied. The titanium concentration at the surface of Ti: LiNbO 3 was ∼7.6 at%, then C Ti gradually decreased to 0.5–0.8 at% аt a depth of ∼4–5 μ m. The combination of the etching technique with non-destructive methods of observation of the created domain structures of a planar type (low-voltage SEM and SHG microscopy) made it possible to detect the effect of titanium concentration on the features of the domain growth. It has revealed that the domain sizes and the average rate of their frontal growth (V f ) in CLN and CLN-0,5Ti are different. The observed differences are discussed in the framework of the current model of the intrinsic defect structure of LiNbO 3 . A peculiar three-dimensional structure of domain gratings in the Ti:LiNbO 3 over the waveguide depth was found. The differences in the formation of the upper and lower parts of periodic gratings in Ti:LiNbO 3 are explained by a significant increase in conductivity near the surface of the waveguide in comparison with deeper layers. The obtained results are useful to match the position and design of planar domain gratings in Ti:LiNbO 3 optical waveguides on non-polar surfaces for better conversion efficiency of integrated nonlinear devices based on quasi-phase-matching.