Band Gap and Edge Engineering via Ferroic Distortion and Anisotropic Strain: The Case of SrTiO3

The effects of ferroic distortion and biaxial strain on the band gap and band edges of SrTiO3 are calculated by using density functional theory and many-body perturbation theory. Anisotropic strains are shown to reduce the gap by breaking degeneracies at the band edges. Ferroic distortions are shown to widen the gap by allowing new band edge orbital mixings. Compressive biaxial strains raise band edge energies, while tensile strains lower them. To reduce the SrTiO3 gap, one must lower the symmetry from cubic while suppressing ferroic distortions. Our calculations indicate that, for engineered orientation of the growth direction along [111], the SrTiO3 gap can be controllably and considerably reduced at room temperature.