First-principles prediction of p-type doping of β-Ga2O3 ultrawide bandgap semiconductors

β-Ga2O3 is an ultra-wide-band-gap semiconductor with a large intrinsic band gap of 4.8 eV and a high breakdown field of 8 MV/cm. These properties when combined with the availability of high-quality large-area single crystals of β-Ga2O3, make it attractive for power electronic applications than conventional wide-band-gap semiconductors such as GaN and SiC. However, the efficiency of β-Ga2O3 devices is currently limited by the lack of good p-type dopants. We present evidence based on first-principles density-functional theory calculations that β-Ga2O3 can be efficiently doped p-type by bismuth. Based on formation energies, we predict that bismuth acts as a substitutional dopant at the gallium site. At low concentrations, bismuth leads to delocalized states just above the valence band edge of β-Ga2O3. These states arise due to the antibonding interaction between the occupied 6s2 lone pair electrons of bismuth and the 2p states of oxygen. The occupancy of these delocalized defect states can be controlled by moving the Fermi level, which can lead to efficient p-type doping.