Band gap modulation via internal electric field control in Ruddlesden-Popper oxides

Ruddlesden-Popper (RP) oxides are perovskite-derived structures whereby the perovskite “blocks” are partially connected and form a quasi-two-dimensional structure. Recently a density functional theory (DFT) study predicted (LaSr)AlO₄ n=1 RP-oxides to show an insulator-metal transition beyond which only band gap variations were previously predicted when A-cation elements are properly ordered. The inequivalent charge states of La³⁺ and Sr²⁺ generate internal electric fields, which induces a sub-nanoscale band bending [1]. Although the internal electric field profile of systems with strong ionic character can be predicted by an ionic model, systems with valence d-orbitals easily deviate from the simple prediction. Here, we examine the interplay between d-orbital and internal electric fields created by atomic arrangements based on DFT calculations. We conclude by summarizing our findings into a set of working principles for band gap control, without chemical doping or changes in cation stoichiometry.
[1] Y.Shin and J.M. Rondinelli , “Tunable band structures in digital oxides with layered crystal habits”, Phys. Rev. B 96, 195108 (2017).