Hole trapping and acceptor dopants in κ-Ga₂O₃

Self-trapped holes, isoelectronic dopants and acceptor impurities in κ-Ga₂O₃ were studied using hybrid density functional theory in the supercell approximation.  Hole self-trapping occurs in each system studied and is stabilized further by the inclusion of acceptor dopant atoms.  Positive charge transition levels within the band gap, along with the appearance of partially occupied electronic band gap states reveal the effect of hole trapping on the electronic structure.  Optical properties exhibit a pronounced red shift and the emergence of visible light peaks in all systems arising from the presence of self-trapped holes.  In each case, the hole localizes on O atoms near the defect with an p-orbital character.  Although p-type doping may be challenging in this polymorph, the acceptor dopants introduce charge transition levels within approximately 0.2 eV from the valence band maximum.  Mitigating self-compensation as the dopant concentration is increased to achieve p-type doping is therefore essential to unpin the Fermi level and shift it towards the valence bands.