8 research outputs found
Band Gap and Edge Engineering via Ferroic Distortion and Anisotropic Strain: The Case of SrTiO
The effects of ferroic distortion and biaxial strain on the band gap and band
edges of SrTiO (STO) are calculated 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 STO 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 STO gap can be controllably and considerably
reduced at room temperature.Comment: 5 pages, 5 figures. To be published in Phys. Rev. Let
Photoinduced defects in a-Si:H Films and InGaN/GaN multiple quantum well structures doped with Eu, Sm, and Eu + Sm
Self trapping of the d-d transfer exciton in bulk NiO evidenced by X-ray excited luminescence
Soft X-ray (XUV) excitation did make it possible to avoid the predominant role of the surface effects in luminescence of NiO and revealed a bulk luminescence with a puzzling well isolated doublet of very narrow lines with close energies near 3. 3 eV which is assigned to recombination transitions in self-trapped d-d charge transfer (CT) excitons formed by coupled Jahn-Teller Ni + and Ni 3+ centers. The conclusion is supported both by a comparative analysis of the CT luminescence spectra for NiO and solid solutions Ni xZn 1 - xO, and by a comprehensive cluster model assignment of different p-d and d-d CT transitions, their relaxation channels. To the best of our knowledge, it is the first observation of the luminescence due to self-trapped d-d CT excitons. © 2012 Pleiades Publishing, Ltd