Band Gap Engineering and Electronic Property Modulation of β-Ga₂O₃ through Bi₂O₃ Alloying

Bismuth (Bi) has recently emerged as a promising dopant for engineering the valence band of Ga₂O₃ to enable p-type doping. This study investigates the structural, electronic and optical effects of Bi incorporation in the ternary oxide (Bi_xGa_1-x)₂O₃ (x = 0 to 0.08) using a combination of experiments and density functional theory (DFT) calculations. Alloying Ga₂O₃ with Bi₂O₃ induces an upward shift of 0.37 eV in the valence band maximum (VBM) while preserving the monoclinic crystal structure. The band gap decreases from 4.97 to 4.57 eV, and the electrical conductivity of the (Bi_xGa_1-x)₂O₃ films reduces by over 2 orders of magnitude as the Bi fraction increases. This conductivity reduction is attributed to greater electron carrier compensation arising from the VBM upshift and a larger effective electron mass. Enhanced defect-related luminescence is observed in (Bi_xGa_1-x)₂O₃, in agreement with DFT calculations showing that the presence of nearby Bi atoms reduces the formation energy of Ga vacancies from 3.69 to 1.43 eV. These findings highlight the potential of Bi₂O₃ alloying for band structure engineering in Ga₂O₃ to facilitate p-type doping.