Thickness effects on photoinduced current in ferroelectric (Pb0.97La0.03)(Zr0.52Ti0.48)O3 thin films

Ferroelectric (Pb0.97,La0.03)(Zr0.52,Ti0.48)O3 thin films in different thicknesses were fabricated on Pt∕Ti∕SiO2∕Si substrates through a sol-gel process. Film thickness dependence of photoinduced current was investigated under the illumination of ultraviolet light. A theoretical model was developed to describe the thickness-dependent photocurrent. Both the theoretical model and experimental results showed that the photocurrent increases exponentially with the decrease in film thickness. However, photocurrent may drop in the films with the very small thickness of tens of nanometers and below in which the small size effect of ferroelectricity is considered. This model also reveals the relationship between the photocurrent and the internal electric field or remnant polarization and predicts a small diffusion current in the opposite direction at very low field or polarization region. These results provide useful guides for the design of ferroelectric film photovoltaic devices.