Tuning the electronic structure of SrTiO3/SrFeO3−x superlattices via composition and vacancy control

Using density functional theory-based calculations, we explore the effects of oxygen vacancies and epitaxial layering on the atomic, magnetic, and electronic structure of (SrTiO3)n(SrFeO3−x)1 superlattices. While structures without oxygen vacancies (x = 0) possess small or non-existent band gaps and ferromagnetic ordering in their iron layers, those with large vacancy concentrations (x = 0.5) have much larger gaps and antiferromagnetic ordering. Though the computed gaps depend numerically on the delicate energetic balance of vacancy ordering and on the value of Hubbard U eff used in the calculations, we demonstrate that changes in layering can tune the band gaps of these superlattices below that of SrTiO3 (3.2 eV) by raising their valence band maxima. This suggests the possibility that these superlattices could absorb in the solar spectrum, and could serve as water-splitting photocatalysts