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 (BixGa1–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 (BixGa1–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 (BixGa1–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.