Ferroelectric polarization-leakage current relation in high quality epitaxial Pb(Zr, Ti)O3 films

Leakage current measurements were performed on epitaxial, single-crystal quality Pb(Zr,Ti)O-3 films with thicknesses in the 50-300 nm range. It was found that the voltage behavior of the leakage current has a minor dependence on thickness, which rules out the space-charge limited currents as main leakage source. Temperature-dependent measurements were performed to obtain more information on the transport mechanism through the metal-ferroelectric-metal (MFM) structure. The results are analyzed in the frame of interface-controlled Schottky emission. A surprisingly low value of only 0.12-0.13 eV was obtained for the potential barrier, which is much smaller than the reported value of 0.87 eV [I. Stolichnov , Appl. Phys. Lett. 75, 1790 (1999)]. The result is explained by the effect of the ferroelectric polarization on the potential barrier height. The low value of the effective Richardson constant, of the order of 10(-7)-10(-6) A/cm(2) K-2, suggests that the pure thermionic emission is not the adequate conduction mechanism for epitaxial MFM structures. The true mechanism might be interface-controlled injection, followed by a low mobility drift through the film volume.