Effect of Alloying Metal Elements on the Valence Band of β-Ga₂O₃: A First-Principles Study

β-Ga₂O₃ is a candidate semiconductor material for high-power electronics due to its ultrawide bandgap and high Baliga's figure of merit. However, its p-type doping is extremely difficult because of its low and flat band dispersion at its valence band maximum (VBM). A few reports have predicted that the VBM of β-Ga₂O₃ can be enhanced via alloying a specific metal (M), which enables p-type conduction. To fully understand the M regulation on the valence band of β-Ga₂O₃, 49 different M-alloyed β-Ga₂O₃ i.e., β-(M_0.125Ga_0.875)₂O₃, are investigated in this work through first-principles calculations. The alloys' configurations and electronic structures are found dependent more on the group number of M. The β-(M_0.125Ga_0.875)₂O₃ members with Ms in groups 3, 9, 13, and 15 and the Ms of Be, Cr, and Fe are semiconductors. The VBMs' energies are enhanced by more than 1 eV in the β-(M_0.125Ga_0.875)₂O₃ for the Ms of Rh, Ir, Sb, and Bi because these VBMs are newly formed by the orbital hybridization of the Ms and neighboring oxygen atoms. The band dispersions at VBMs generally become steeper, especially for Ms in groups 13 and 15. The average hole effective mass in β-(Al_0.125Ga_0.875)₂O₃ is only 3.43% of that in the β-Ga₂O₃. It is believed that the reduced hole effective mass and increased VBMs' energies make the p-type doping easier in these alloys and the applications of the alloys wider.