Structure and optical properties of ferroelectric PbZr _0.40Ti_0.60O₃ films grown on LaNiO ₃-coated platinized silicon determined by infrared spectroscopic ellipsometry

The PbZr_0.40Ti_0.60O₃ (PZT)/LaNiO ₃ (LNO) multilayer films with different associated thickness have been deposited on Pt/Ti/SiO₂/Si substrates by a modified sol-gel technique. X-ray diffraction analysis shows that the PZT and LNO films are polycrystalline with the (100)-preferential orientation and perovskite phase. The optical properties of PZT films have been investigated using infrared spectroscopic ellipsometry (IRSE) in the photon frequency range of 800-4000 cm^-1 (2.5-12.5 μm). By fitting the measured ellipsometric parameters with a four-phase layered model (air/PZT/LNO/Pt) and a derived classical dispersion relation, the optical function and thickness of the films have been uniquely extracted. The refractive index of the PZT films increases and the extinction coefficient decreases with increasing grain size in the mid-infrared region. Correspondingly, infrared absorption coefficient of the films linearly increases with increasing thickness. It can be concluded that the discrepancy of infrared optical properties is mainly ascribed to the crystalline quality, the grain size effect, and the influence from the interface layer. The present results can be crucial for future application of ferroelectric PZT-based infrared optoelectronic devices.