Transient carrier transport and rearrangement of Schottky barrier layers under the action of a bias applied to the M/PZT/M structure

Abstract

A drift-diffusion model of unsteady carrier transport in an M/lead zirconate titanate (PZT)/M structure is proposed. It is assumed that the PZT film has electronic conductivity. Electrons are generated by oxygen vacancies and trapped by Ti+3 deep centers. It is assumed that electrons move in the electric field by hopping between titanium atoms, with an effective mobility that is considered constant. To account for the polarization, it is believed that, near the contacts, there are thin defective layers in which the polarization is zero, while outside these layers, the polarization does not vary across the film thickness and depends on the applied bias. The model was used to account for the formation of the current peak in the current–voltage curves, which is not caused by the domain switching and observed in epitaxial films only when the bias and polarization directions coincide. It is shown that a pronounced current peak is formed when (а) an accumulated space-charge layer appears near one of the contacts under the action of polarization and (b) this contact is cathode, which is only possible when the polarization and bias directions coincide. As a result, electrons flow between space-charge layers, and the film resistance first decreases and then starts to increase again, and this gives rise to a current peak. It is shown that this effect is purely nonstationary. The model also made it possible to estimate the basic parameters of the structure: electron mobility, density of oxygen vacancies, dielectric constant, defect layer thickness, and barrier height.