Electron mobility in ordered β-(Al_xGa_1−x)₂O₃ alloys from first-principles

Alloying Ga₂O₃ with Al₂O₃ yields diverse structural phases with distinctive optoelectronic properties, making them promising candidates for ultrawide bandgap semiconductors in next-generation power electronics. Yet, there is a lack of sound knowledge of the carrier dynamics in the (Al_xGa_1−x)₂O₃ alloys due to their structural complexity. Herein, we focus on the ordered β-(Al_xGa_1−x)₂O₃ alloys, predict their carrier mobility, and determine the intrinsic electron mobility limit based on solving linearized Boltzmann transport equations from first principles. The predicted electron mobility for ordered β-(Al_0.25Ga_0.75)₂O₃ and β-(Al_0.5Ga_0.5)₂O₃ alloys at 300 K, respectively, is 103.6 and 80.60 cm²/V s, demonstrating excellent agreement with literature experiments. Such low electron mobility is limited by the intrinsically strong polar optical phonon (POP) scattering process. As the Al content further increases, the alloy's electron mobility further reduces mainly due to the enlarged Pauling ionicity, Fröhlich coupling constant, and POP scattering. This work provides physical insight into the carrier dynamics in ordered β-(Al_xGa_1−x)₂O₃ alloys and seeks to improve the electron mobility for potential applications in high-power electronics.