Microwave dielectric and nonlinear optical studies on radio-frequency sputtered Dy2 O3 -doped KNN thin films

We report the effect of oxygen mixing percentage (OMP) on structural, microstructural, dielectric, linear, and nonlinear optical properties of Dy2O3-doped (K0.5Na0.5)NbO3 thin films. The (K0.5Na0.5)NbO3 + 0.5 wt%Dy2O3 (KNN05D) ferroelectric thin films were deposited on to quartz and Pt/Ti/SiO2/Si substrates by RF magnetron sputtering. An increase in the refractive index from 2.08 to 2.21 and a decrease in the optical bandgap from 4.30 to 4.28 eV indicate the improvement in crystallinity, which is also confirmed from Raman studies. A high relative permittivity (er=281-332) and low loss tangent (tanδ=1.2%-1.9%) were obtained for the films deposited in 100% OMP, measured at microwave frequencies (5-15 GHz). The leakage current of the films found to be as low as 9.90×10−9 A/cm2 at 150 kV/cm and Poole-Frenkel emission is the dominant conduction mechanism in the films. The third order nonlinear optical properties of the KNN05D films were investigated using modified single beam z-scan method. The third order nonlinear susceptibility (ǀχ(3)ǀ) values of KNN05D films increased from 0.69×10−3 esu to 1.40×10−3 esu with an increase in OMP. The larger and positive nonlinear refractive index n2=7.04×10−6 cm2/W, and nonlinear absorption coefficient β=1.70 cm/W were obtained for the 100% OMP film, indicating that KNN05D films are good candidates for the applications in nonlinear photonics and high-frequency devices.