Photoelectric evaluation of polarization and internal field in PZT thin films

Photoelectric phenomena were investigated in sol-gel derived lead zirconate-titanate (PZT) films. Two major illumination techniques were employed in order to assess both the ferroelectric polarization and internal field in the films. Using semitransparent top electrodes and short UV pulses, the fast polarization-dependent photocurrent was observed and attributed to bulk photovoltaic effect. This current can be used for non-destructive readout of polarization state in non-volatile ferroelectric memories. In the other regime, opaque electrodes were employed and a steady-state current (or voltage in the open circuit conditions) was investigated caused by the illumination of the area adjacent to the top electrode. This polarization-independent current was ascribed to the internal field due to oxygen-deficient layer near the film's surface. It is shown that the observed photocurrent is sensitive to the wavelength of the light and can be used for the evaluation of electron band bending and electrical inhomogeneities across the film's thickness.