Fermi level engineering in doped BaTiO3 multilayers

Mario Maglione ¹ Christopher Castro Chavarría ^1,2 Sandrine Payan ¹ Alla Artemenko ¹ Andreas Klein ²

¹Centre National de la Recherche Scientifique, Université de Bordeaux, UMR 5026, Institut de Chimie de la Matière Condensée de Bordeaux, Pessac, France
²Technische Universität Darmstadt, Department of Materials and Earth Sciences, Electronic Structure of Materials, Darmstadt, Germany

As in any semiconductor, the Fermi level of ferroelectric Materials is tuned under heterovalent substitution. We have used Nb, La and Mn as such dopants in BaTiO3 thin films and multilayers. We first show that in-situ XPS is a very efficient tool for probing the Fermi level position in the bulk of the films and its bending at interfaces. In the case of Nb/La multilayers, a large bending was shown to arise from extended cross-diffusion between the layers and an exceptional overall dielectric permittivity resulted [1]. Such an extrinsic behaviour may be ascribed to space charge accumulation at interfaces on donor levels in the band gap close to the bottom of the conduction band.

On the other hand, Mn acceptor doping is able to restore and intrinsic behaviour of BaTiO3 films which are usually very sensitive to unwanted oxygen vacancies. Such curing effect of Mn doping has already been used in many instances for BaTiO3 ceramics or thin films. By following the Fermi level position by in situ XPS and confirming the electron trapping at Mn sites by EPR, we bring microscopic evidence supporting this model.

[1] Christopher Castro Chavarría, Sandrine Payan, Jean-Paul Salvetat , Mario Maglione and Andreas Klein Fermi Level Engineering for Large Permittivity in BaTiO3-Based Multilayers Surfaces 2020, 3, 567–578; doi:10.3390/surfaces3040038

[2] Christopher Castro Chavarría, Sandrine Payan, Alla Artemenko, Mario Maglione and Andreas Klein, to appear