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 metho d, to provide information on atomic diffusion is analyzed. The analysis foc uses on studying Ti-diffused waveguide layers of LiNbO3 crystals for optoel ectronic applications. Samples were prepared by a deposition of a 35-nm-thi ck 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 interplan ar spacing derived from x-ray diffraction data are compared with the Ti-con centration profiles measured by secondary ion mass spectrometry. It is show n that both results can be used with confidence to determine the Ti-diffusi on coefficients in LiNbO3. Comparison of the two techniques allowed us to o btain a numerical factor, K, relating the Ti concentration and the modifica tion 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 s train contribution to the structural parameters of the waveguide layer. The se variations are attributed to high-temperature phase transformation proce sses, which accompany Ti diffusion. (C) 1999 American Institute of Physics. [S0021-8979(99)10009-4].