High Retention of Polarization in Polycrystalline M/PZT/M Capacitors in the Presence of Depolarization Field Near Grain Boundaries

Recently, we reported on the photovoltaic current observed in poled capacitors with polycrystalline Pb(ZrTi)O-3 (PZT) films, where (111)-oriented PZT grains are separated by an ultrathin semiconductor PbO phase. This photocurrent is driven by the depolarization field, which is generated by residual uncompensated polarization charge located on grain boundaries near electrodes. We showed that the photocurrent can serve as a criterion of existence of the depolarization field and demonstrated that this field is retained in the film for at least one year. Here, we present new experimental and numerical results which confirm the proposed conception of the photovoltaic effect. We study the photocurrent depending on the kind of electrodes, preliminary illumination in an open-circuit regime, and light intensity of LED, and give evidence of retention of the depolarization field in the films for at least for one and one-half years. The numerical study of the photovoltaic effect at extremely high photogeneration rate shows that total compensation of the polarization charge by photoexcited carriers in these structures is impossible. This photovoltaic effect can be used for nondestructive readout in ferroelectric memory.