Er3+ diffusion in congruent LiNbO3 crystal in Li-enriched atmosphere.

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 1130 °C, was attempted. Single-crystal x-ray diffraction, micro-Raman, photoluminescence spectroscopy, and secondary ion mass spectrometry (SIMS) 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 10 nm for an X-cut plate and 15 nm for a Z-cut plate. In this case, the diffusion is complete if the duration is long enough (>150 h) 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 is thicker than 10 nm for the X-cut plate and 15 nm for the Z-cut plate, the diffusion will be incomplete no matter how long the duration is. This is because the residual Er³⁺ ions form irremovable ErNbO₄ grains on the surface of the crystal. SIMS analysis on an X-cut VTE (1130 °C/192 h) and a Z-cut VTE (1129 °C/158 h) crystal coated, respectively, with 10 and 15 nm thick Er film reveals that the Er diffusion shows obvious anisotropy with the mean diffusion coefficients of 0.0155 and 0.0957 μm²/h, respectively. The surface concentrations are 1.5×10²⁰ and 1.0×10²⁰ at./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 is similar to 99.4% for the X-cut sample coated with 10 nm thick Er film and 99.3% for the Z-cut crystal coated with 15 nm thick Er film. The rms roughness of the diffused surface is better than 6 and 4 nm for the X-cut and Z-cut samples, respectively. [ABSTRACT FROM AUTHOR]