Structural modifications in He-implanted waveguide layers of LiNbO3

He-implanted and heat-treated optical waveguide layers in Y-cut LiNbO3 wafers were studied by means of high-resolution X-ray diffraction. The depth-resolved profiles of the lattice parameter were derived from the measured diffraction spectra as a function of annealing temperature. Using these data, the spatial distribution of the electron density related to the post-implantation lattice swelling was determined, which shed light on the waveguide formation in damaged layers. Heat treatments at temperatures T > 200 degrees C resulted in the deterioration of waveguide properties due to annealing of the implantation-induced damage. Lattice recovery was found to be a thermally activated process with an activation energy of E(a) = 0.32 +/- 0.03 eV. This is accompanied by defect clustering, giving rise to diffuse scattering components in the diffraction spectra.