Optical and dielectric studies on radio frequency sputtered Gd2O3 doped K0.5Na0.5NbO3 thin films for nonlinear photonic and microwave tunable device applications

(K0.5Na0.5)NbO3+1 wt%Gd2O3 (KNN1G) ferroelectric thin films have been deposited onto quartz and Pt/Ti/SiO2/Si substrates by RF magnetron sputtering. The increase in the refractive index, and decrease in the optical bandgap was observed with the oxygen mixing percentage (OMP), and were in the range of 2.07-2.19, and 4.30-4.20 eV, respectively. The dispersion in the refractive index was analyzed using Wemple-DiDomenico single-oscillator model. The refractive index dispersion parameter for the film deposited under 100% OMP is found to be 6.64 × 10−14 eV m2. The best microwave (5 GHz-15 GHz) dielectric properties were observed for the film deposited under pure oxygen plasma. The film deposited in 100% OMP show the relative low leakage current density 4.06 × 10−6 A/cm2 at 153 kV/cm and the leakage current of the KNN1G films followed the space charge limited current behaviour. Nonlinear optical property of KNN1G thin films is measured by using modified single beam Z-scan technique. The large third order optical nonlinearity was obtained for the film deposited under pure oxygen plasma with nonlinear refractive index n2 = 2.46 × 10−5 cm2/W, nonlinear absorption coefficient β = 5.02 cm/W, real and imaginary parts of nonlinear susceptibility are χR(3) = 3.07 × 10−3 esu, and χI(3) = 3.16 × 10−3 esu, respectively. The obtained results show that the KNN1G thin films have a great potential for nonlinear photonic applications and high frequency applications.