Diffusion and structural modification of Ti:LiNbO3, studied by high-resolution x-ray diffraction

The ability of high-resolution x-ray diffraction, as a nondestructive method, to provide information on atomic diffusion is analyzed. The analysis focuses on studying Ti-diffused waveguide layers of LiNbO3 crystals for optoelectronic applications. Samples were prepared by a deposition of a 35-nm-thick Ti layer on the 3-in.-Y-cut LiNbO3 wafer and subsequent annealing at 995 degrees C for periods of 0.5-6 h. Depth-resolved profiles of the interplanar spacing derived from x-ray diffraction data are compared with the Ti-concentration profiles measured by secondary ion mass spectrometry. It is shown that both results can be used with confidence to determine the Ti-diffusion coefficients in LiNbO3. Comparison of the two techniques allowed us to obtain a numerical factor, K, relating the Ti concentration and the modification of lattice parameters, i.e., to characterize quantitatively the extent of lattice contraction due to Ti incorporation in the LiNbO3 crystal. The K factor was found to increase with annealing time, indicating a variable strain contribution to the structural parameters of the waveguide layer. These variations are attributed to high-temperature phase transformation processes, which accompany Ti diffusion. (C) 1999 American Institute of Physics. [S0021-8979(99)10009-4].