Stress and film thickness effects on the optical properties of ferroelectric Pb(Zr_xTi_1-x)O₃ films

Spectrophotometry measurements at wavelengths from 180 nm to 3000 nm, x-ray diffraction, and Raman spectroscopy were used in the characterization of polycrystalline Pb(Zr x Ti 1 - x )O 3 films with various thicknesses deposited by pulsed laser deposition on MgO substrates. It was found that films were under a strong compressive stress increasing up to 1.3 GPa with decreasing film thickness down to 80 nm. A clear blue shift of the optical absorption edge was found in transmission spectra leading to an increase of band gap energy from 3.9 eV to 4.5 eV. Both refractive index and extinction coefficient increased at the wavelengths below 500 nm with decreasing film thickness.