The impact of thickness on the optical, electrical and dielectric properties of nanocrystalline 0.9 MTO-0.1BNO composite thin films

The 0.9 MgTiO3–0.1Ba5Nb4O15 (0.9MTO-0.1BNO) thin films deposited on Pt (111)/TiO2/SiO2/Si (100) and SiO2 substrates by RF reactive magnetron sputtering have been reported. The films are deposited at a substrate temperature of 400 °C under 50/50 argon (Ar2)/oxygen (O2) mixed ambiance by varying the film thickness. The X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) studies have confirmed presence of both MTO and BNO phases.. The obtained strain in the films is found to be reduced with an increase in film thickness. The 3d crystal structure of MTO exhibited significant variations in bond length for the films with different thicknesses. The dispersion in the refractive index of the films has obtained using the single electronic oscillator model, and the obtained bandgap value is found to be reduced from 3.75 to 3.34 eV with an increase in film thickness from 150 to 340 nm, accordingly. The films revealed uniform spherical shaped particles with smooth surface with small rms roughness values around 2.9 to 2 nm. The microwave and low frequency dielectric responses showed improvment with an increase in film thickness. The impedance spectroscopy analysis displayed Cole-Cole behavior indicating the non-Debye conduction process present in the films. The frequency dependent conduction process has analyzed by Jonscher's Power law and the non-overlapping small polaron hopping nature has been observed. Extracted activation energies estimated from conductivity are found to be in the range of 0.31 eV to 0.14 eV. The leakage current density (J) with the applied potential has found to be in the range of 10−6 A/cm2 at 100 kV/cm2 for 340 nm film. The obtained results suggest that these films are promising for optical and microwave integrated circuit applications.