Temperature activated optical absorption in SnO₂ from first principles

The optical and excitonic properties are at the heart of applications of many electronic materials and symmetry is an important governing factor of optical absorption, via dipole selection rules. These determine whether the lowest electron-hole transition is optically allowed or forbidden. For indium oxide, inclusion of lattice vibrations in calculations has shown to make the static lattice level dipole forbidden transitions allowed ¹. This is explained by relaxation of dipole selection rules as lattice symmetry undergoes a change via introduction of phonons. We perform first principles simulations in density functional theory framework to study this phenomenon in a dark state hosting material, bulk SnO₂ ² . Moreover, by solving Bethe-Salpeter equation, the effect of phonon induced temperature on excitonic effects is investigated. Our results confirm the brightening of the dark states, show a redshift of the absorption onset as well as modifications in absorption coefficients. This work provides a more accurate picture of the electronic and optical properties of this important transparent conducting oxide.

1. Morris, A. J. & Monserrat, B. Optical absorption driven by dynamical symmetry breaking in indium oxide. Phys. Rev. B 98, 161203 (2018).

2. Schleife, A. et al. Tin dioxide from first principles: Quasiparticle electronic states and optical properties. Phys. Rev. B 83, 035116 (2011).