Mechanisms of electron transport in BaTiO3 ultrathin epitaxial films in the temperature range 40 K-295 K

In this paper, we report the results of experimental study of electron transport mechanisms in ferroelectric BaTiO3 ultrathin epitaxial films in a broad temperature range. For this purpose ferroelectric tunnel junctions based on STO/LSMO/BTO/Au structures were fabricated with different thicknesses of ferroelectric films (from 3 to 12 nm). Ferroelectric and electrical properties of heterostructures were measured at temperatures ranging from 40 K to 300 K. Based on experimental results, we find that prevailing transport mechanisms in BaTiO3 epitaxial thin film is determined by the film thickness. Below the certain thickness of the BaTiO3 film, a dominant contribution in the current through the structure is due to elastic tunneling. Increasing the thickness of the ferroelectric film leads to an impact from inelastic tunneling, mainly due to an interaction with traps caused by cation and anion vacancies in oxide sub-lattices. We suppose that the specificity of transport mechanisms in BaTiO3 ultrathin films is defined by the ratio of film thickness and the mean free path of injected electrons, along with repolarization processes synchronized with the ferroelectric coercive field. The latter point has been confirmed by the results of experimental study in a broad temperature range.