The thermal diffusion of Er3+ into X- and Z-cut congruent LiNbO3 crystal in Li-enriched atmosphere [i.e., vapor transport equilibration (VTE)], created by Li3NbO4–LiNbO3 two-phase powder at the temperature around 1130C, was attempted. Single-crystal X-ray diffraction, micro-Raman, photoluminescence spectroscopy, and secondary ion mass spectrometry were used to study the crystalline phase with respect to Er3+ ion and the Er3+ diffusivity. The results show that the thickness of the Er film coated should not be thicker than 10nm for an X-cut plate and 15nm for a Z-cut plate. In this case, the diffusion was complete if the duration was long enough (>150h) and the Er3+ ions in the diffused layer still retain the LiNbO3 phase. On the other hand, if the initial thickness of the Er metal film was thicker than 10nm for the X-cut plate and 15nm for the Z-cut plate, the diffusion will be incomplete no matter how long the duration is. This was because the residual Er3+ ions form irremovable ErNbO4 grains on the surface of the crystal. SIMS analysis on an X-cut VTE (1130C/192h) and a Z-cut VTE (1129C/158h) crystal coated, respectively, with 10 and 15nm thick Er film reveals that the Er diffusion shows obvious anisotropy with the mean diffusion coefficients of 0.0155 and 0.0957µm2/h, respectively. The surface concentrations were 1.5 x 1020 and 1.0 x 1020at/cm3, respectively. The diffused Er3+ ions follow the stretched-exponential decay profile with a stretching factor of 1.85 and 3.5, respectively. The Li/Nb ratio in the Er-diffused layer was similar to 99.4% for the X-cut sample coated with 10nm thick Er film and 99.3% for the Z-cut crystal coated with 15nm thick Er film. The root mean square roughness of the diffused surface was better than 6 and 4nm for the X-cut and Z-cut samples, respectively.

Er3+ Diffusion in Congruent LiNbO3 Crystal in Li-Enriched Atmosphere. D.L.Zhang, Q.S.Jia, P.R.Hua, P.Zhang, W.J.Zhang, Q.Z.Yang, H.L.Liu, Y.M.Cui, E.Y.B.Pun: Journal of Applied Physics, 2007, 102[7], 073525