Self-trapped holes and acceptor impurities in orthorhombic Ga2O3

The electronic and optical properties of self-trapped holes in kappa-phase orthorhombic Ga2O3 in conjunction with isoelectronic and acceptor dopants were studied using hybrid density functional theory. Hole trapping was found to be energetically favorable in all systems investigated and was further stabilized by acceptor dopants with large ionization energies. The electronic structures revealed emergent states in the band gap ranging from 0.2 to 1.2 eV above the valence band maximum, primarily composed of O 2p orbitals in all cases, with a notable contribution from Zn 3d orbitals in the Zn-doped system. Hole trapping resulted in a pronounced red shift and the emergence of additional absorption peaks, producing optical characteristics that were in closer agreement with experimental observations. In each system, the trapped hole localized near the dopant atom, predominantly on adjacent O atoms, accompanied by local lattice distortions. The valence band remained largely non-dispersive even in the presence of a hole; hole states lied near the Fermi level for isoelectronic dopants and deeper in the band gap for acceptor dopants. These findings indicate that isoelectronic doping may find an avenue for p-type doping in this polymorph of Ga2O3 if a means to mitigate self-compensation is found.