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-(M0.125Ga0.875)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-(M0.125Ga0.875)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-(M0.125Ga0.875)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-(Al0.125Ga0.875)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.