EFFECTS OF LASER-RADIATION ON PHOTOCONDUCTIVITY IN PZT THIN-FILMS

Excitation photocurrent spectroscopy (EPS) was used to record photoconductivity from 200 to 600 nm for a Pb(Zr0.53Ti0.47)O-3 (PZT) thin film. Four spectral bands at 262, 338, and 428/472 nm were observed and assigned tentatively to originate from Pb3+, O++(vacancy center) and Fe3+ (impurity and/or ion-doped) centers, respectively. When the band at 262 nm in the PZT film was excited using a KrF laser (248 nm), the photoconductivity at 262 nm enhances as observed in EPS. The resistivity decreases by a factor of 7 as compared to the unexposed sample that caused the P-E hysteresis loop to broaden along the polarization axis. When the band at 338 nm was pumped by a N-2 laser (337 nm), the P-E hysteresis loop shows a reduction in the polarization and a 26-fold increase in the resistivity. The results are consistent with the generation of shallow trapping states that dominated the production of dark current in EPS. It is suggested that KrF laser creates the conductive Pb3+ hole traps and N-2 laser mainly generates the shallow defects having antiparallel dipoles. The presence of charge trapping centers in PZT thin films is discussed in terms of its application in optical memory devices.