Effect of annealing conditions on the electrical properties of ALD-grown polycrystalline BiFeO3 films

Abstract

An investigation of the influence of annealing conditions on the carrier transport, leakage current and dielectric properties of ALD-grown amorphous Bi–Fe–O thin films after their crystallization into BiFeO₃ is presented. Whereas the interface-limited Schottky emission mechanism is dominant in 70 nm thick Fe-rich films after relatively short annealing, a space-charge-limited conduction mechanism is dominant in stoichiometric films with a thickness of 215 nm independent of the annealing conditions. Interestingly, prolonged annealing of the thin films also results in space charge limited conduction. Analysis of the changes in dielectric properties, on one hand, and the film composition, microstructure and morphology, on the other hand, reveal the key role of grain boundary interfaces for the conductivity of the polycrystalline ALD-grown BiFeO₃ thin films. Extended annealing in oxygen results in 2–3 orders-of-magnitude reduction in leakage current accompanied by decreases in dielectric loss, highlighting the importance of optimizing annealing conditions for any applications of BiFeO₃ thin films.