Illumination effects on the ferroelectric and photovoltaic properties of Pb_(0.95)La_(0.05)Zr_(0.54)Ti_(0.46)O_3 thin film based asymmetric MFM structure

摘要

We report the effects of illumination on the ferroelectric and photovoltaic properties of the Pb_(0.95)La_(0.05)Zr_(0.54)Ti_(0.46)O_3 (PLZT) thin film based asymmetric metal/ferroelectric/metal capacitor structure, using Au as a top electrode and Pt as a bottom electrode. Conductive-AFM (atomic force microscopy) measurements demonstrate the evolution of charge carriers in PLZT films on illumination. The capacitance-voltage, the polarization-electric field, and the leakage current-voltage characteristics of the asymmetric Au/PLZT/Pt capacitor are discussed under dark and illuminated conditions. The light generates charge carriers in the film, which increase the coercive field and net remnant polarization and decrease the capacitance. The leakage current of the capacitor increases by an order of magnitude upon illumination. The leakage current data analyzed to study the conduction mechanism shows that the capacitor structure follows the Schottky emission "1/4" law. The illuminated current density-voltage curve of the capacitor shows non-zero photovoltaic parameters. An open circuit voltage (V_(oc)) of -0.19 V and a short circuit current density (J_(sc)) of 1.48 μA/ cm~2 were obtained in an unpoled film. However, after positive poling, the illuminated curve shifts towards a higher voltage value resulting in a V_(oc) of -0.93 V. After negative poling, the curve shows no change in the V_(oc) value. For both poling directions, the J_(sc) values decrease. The photocur-rent in the capacitor shows a linear variation with the incident illumination intensity.