Secondary ion mass spectrometry study of Ti⁴⁺ diffusion properties in congruent Er:LiNbO₃ codoped with moderate concentration of MgO

At 1100 °C, the diffusion properties of Ti⁴⁺ into congruent LiNbO₃ crystals codoped with 0.5 mol% Er₂O₃ and different MgO concentrations of 0.5, 1.0, and 1.5 mol% have been studied by secondary ion mass spectrometry (SIMS). Three Y-cut and three Z-cut plates with different Mg doping levels were coated with a 60-nm-thick Ti film at first and then annealed at 1100 °C for 28 h in a wet O₂ atmosphere. SIMS was used to analyze depth profile characteristics of diffused Ti ions and the constituent elements of the substrate as well. The results show that the diffusion reservoir was exhausted and the Ti metal film was completely diffused. All measured Ti profiles follow a Gaussian function. No Mg out-diffusion accompanied the Ti in-diffusion procedure for all crystals studied. The l/e diffusion depth is similar to 8.3/10.2, 7.4/8.7, and 6.6/8.2 ± 0.2/0.2 um/um for the Y/Z- cut crystal with the Mg doping level of 0.5, 1.0, and 1.5 mol%, respectively, yielding a Ti⁴⁺ diffusivity of 0.62/0.93, 0.49/0.67, and 0.39/0.60 ± 0.03/0.03 (um2/h)/(um2/h), respectively. The diffusion shows definite anisotropy and a considerable MgO doping level effect. Under the same Mg doping level, the diffusion in a Z-cut crystal is faster. The diffusivity decreases with the increase of the Mg doping level. This effect is qualitatively explained from the viewpoint of the Mg doping effect on concentration of the intrinsic defects in LiNbO₃ crystal.