Polarization control and domain manipulation in ferroelectric films with uv light

Polarization measurements were performed in sol-gel derived PZT films during illumination with UV light through semitransparent electrodes. Strong deformation of polarization hysteresis loops was observed including asymmetric shift, reduced tilt, pinching and selective suppression of the remanent polarization. All the observed effects are attributed to local internal fields created near the interfaces and domain boundaries by the trapped charge carriers excited by the UV light. The estimated surface density for trapped charge is about 91012 cm-2 for electrons and 4.31012 cm-2 for holes. The space charge field results in a stable deformation of the hysteresis loops similar to that observed after aging, which can be only reversed by heating/electric field cycling. On the other hand, the remanent polarization measured by piezoelectric technique is only slightly reduced by the UV light. The origin of the observed effects and their implications for thin-film devices are discussed.