Optical Absorption Spectra of In2O3 and Ga2O3 from First-Principles Calculations

"Optical Absorption Spectra of In2O3 and Ga2O3 from First-Principles Calculations" -- Andre Schleife, University of Illinois at Urbana-Champaign

Highly transparent and conducting materials are desirable in the context of transparent electronics, photovoltaics, and optoelectronics. Indium oxide (In2O3) and gallium oxide (Ga2O3) exhibit these material properties: their electrical conductivity can be controlled over a large range while exhibiting remarkable transparency over the visible spectrum. While they have been adopted as transparent conducting oxide layers and as standalone semiconductors, their fundamental optical properties are still poorly understood. High-quality single crystals are recently available but theoretical efforts have been hampered by the complexity of unit cells containing up to 40 atoms. Using state-of-the-art first-principles calculations based on the Bethe-Salpeter approach, we provide the most accurate theoretical optical spectra currently available for these materials. We identify a pronounced influence of excitons near the absorption edge and over a large range of photon energies. Our results advance the understanding of optical anisotropy in Ga2O3 and quantitatively describe the observed shifts with high accuracy.