Process-Structure-Property Relationship in PLZT Thin Films for UV Sensing: Influence of Film Thickness and Sol-Gel Solution Preparation Routes on Ferroelectric, Optical and Photovoltaic Properties

Lead lanthanum zirconate titanate (PLZT) is a ferroelectric material that exhibits excellent electro-optic and photovoltaic properties, making it a suitable candidate for optoelectronic applications. Among thin film deposition techniques, sol-gel method is preferred for its precise stoichiometric control, low processing temperature, cost effectiveness, and scalability. However, achieving repeatable results remains a major challenge. Different sol-gel preparation routes, which vary in solvent evaporation rates, reaction temperatures, and chemical environment, can significantly influence the microstructure and properties of the resulting films. Therefore, understanding the influence of sol-gel preparation routes on ferroelectric, optical, and photovoltaic properties is essential for ensuring reliable device performance. This study investigates the influence of film thickness, annealing temperature, and three sol-gel solution preparation routes: open-beaker (Sol1), reflux (Sol2), and reflux with distillation (Sol3), on ferroelectric, optical, and photovoltaic properties of Pb_0.95 La_0.05 Zr_0.54 Ti_0.46 O_3 thin films. PLZT films were fabricated on platinized silicon substrates by spin coating, and platinum top electrodes were sputtered to form capacitor structures for ferroelectric and photovoltaic measurements. Characterization was performed using X-ray diffraction, ultraviolet-visible spectroscopy, Raman spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and spectroscopic ellipsometry. A strong dependence of crystallite size, strain, capacitance, remnant polarization, leakage current, photocurrent, and free carrier concentration was observed on the film thickness. Films with 135 nm thickness exhibit the most optimized performance with highest remnant polarization, photocurrent, free carrier concentration, and lowest strain and leakage current. The annealing temperature showed minimal effect on optical properties. Comparative studies of the sol-gel routes revealed that Sol3 produced films with enhanced crystallinity, uniform morphology, larger grain size, lower surface roughness, and stoichiometry closest to the target composition. Ferroelectric, optical, and photovoltaic measurements confirmed that Sol3 yielded superior and repeatable properties, including large remnant polarization, high photocurrent, low leakage, strong ultraviolet (UV) absorption, lower optical band gap, higher refractive index and extinction coefficients. Thus, reflux with distillation method is the most reliable and reproducible route for developing high-quality PLZT thin films for optoelectronic devices, particularly UV sensors.