Approximate Quasiparticle DFT+A-½ Method Applied to Ga₂O₃ and In₂O₃ Polymorphs

Gallium oxide (Ga₂O₃) and indium oxide (In₂O₃) are at the forefront of the recent progress in power semiconductor devices, which extend the range of power semiconductors from wide bandgap semiconductors (WBS) such as GaN and SiC to ultra-wide bandgap semiconductors (UWBS) such as Ga₂O₃ and Al₂O₃, sometimes alloyed with In₂O₃. These oxide semiconductors currently find themselves at a stage of development similar to that of the WBG semiconductors in the 1980s and therefore, several challenges related to the understanding of their properties have to be settled yet. Specifically for these oxides the well-known underestimation of DFT-based bandgap prediction is more complicated because it is also connected with the wrong position of the d-level in disagreement with the experimental results. Several techniques can be used to overcome these difficulties, but, in general, state-of-the-art methods (such as GW and hybrid functionals), are computationally extremely expensive, which makes them impractical for more complex systems as it is required for a deep investigation for these oxides with pronounced polymorphism and the need for large unit cells.<br/>In this study we investigate the structural, optical and electronic properties of ten polymorphs of Ga₂O₃ and In₂O₃ using a fast and efficient approximate quasiparticle method called DFT+A-½ which at the same time could deal with the delocalized d-levels and the problem in underestimation of the energy bandgap. We provide approximate quasiparticle band structures and binding energies even for very complex systems such as defective spinel phase of Ga₂O₃ containing 160 atoms in a cell. Our results are in line with the state-of-the-art methods and experimental data providing energy bandgaps of about 4.6 eV to 5.1 eV for Ga₂O₃ polymorphs and, 2.4 eV to 3.3 eV for In₂O₃ polymorphs. Band edge optical properties including excitonic effects are explained in terms of effective masses and dielectric constants. Furthermore, we predict pressure-induced phase transitions between polymorphs of the same oxides derived from equations of state.