Short-circuit photocurrent in epitaxial lead zirconate-titanate thin films

Photovoltaic properties of the metal-ferroelectric-metal structures, having $SrRuO3$ metal oxide electrodes and $Pb(Zr,Ti)O3$ (PZT) as ferroelectric layer, are investigated by the short-circuit photocurrent (SC-PHC) in the $200–800nm$ wavelength domain. The band-gap dependence on the Zr content was determined from the spectral distribution of the SC-PHC signal. It was found that the band-gap value increases linearly with the Zr content, from about $3.9eV$ to about $4.4eV$⁠. It is shown that the sign and the magnitude of the signal depend on the internal bias and on the spontaneous polarization direction and value. The photocurrent describes a hysteresis loop similar to that of the ferroelectric polarization and can be used as a nondestructive readout of the nonvolatile memories based on PZT films. The existence of a significant SC-PHC signal at wavelengths corresponding to subgap energies is attributed to the presence of charged, deep levels in the forbidden band. It is also shown that the epitaxial PZT films have the potential for solid-state UV detectors, with current responsivity as high as $1mA∕W$⁠. The results are not entirely consistent with a bulk photovoltaic effect and are discussed in the frame of a Schottky barrier model for the metal-ferroelectric interface.