Band alignment characterizations of grafted GaAs/ ( 2 ¯ 01 ) Ga₂O₃ heterojunction via x-ray photoelectron spectroscopy

Research on gallium oxide (Ga₂O₃) has accelerated due to its exceptional properties, including an ultrawide bandgap, native substrate availability, and n-type doping capability. However, significant challenges remain, particularly in achieving effective p-type doping, which hinders the development of Ga₂O₃-based bipolar devices like heterojunction bipolar transistors (HBTs). To address this, we propose integrating mature III-V materials, specifically n-AlGaAs/p-GaAs as the emitter (E) and base (B) layers, with n-Ga₂O₃ as the collector (C) to form III-V/Ga₂O₃ n-p-n HBT. This hetero-material integration could be achieved using advanced semiconductor grafting techniques that could create arbitrary lattice-mismatched heterojunctions by introducing an ultrathin dielectric interfacial layer. This study focused on revealing the band alignment at the base-collector (B-C) junction using a n-Ga₂O₃ ( 2 ¯ 01 ) orientated substrate combined with p-GaAs for potential HBT applications. We discovered a type-II band alignment between p-GaAs and Ga₂O₃ ( 2 ¯ 01 ) , with the p-GaAs conduction band approximately 0.614 eV higher than that of Ga₂O₃ ( 2 ¯ 01 ) . This staggered alignment allows for direct and efficient electron transport from the p-GaAs base to the n-Ga₂O₃ collector, avoiding the electron blocking issues present in p-GaAs/Ga₂O₃ (010) heterojunctions. Additionally, our study suggests the potentially existing type-II alignment between the ( 2 ¯ 01 ) and (010) Ga₂O₃ interfaces, highlighting the orientation-dependent band offsets. These findings are pivotal for developing high-performance Ga₂O₃-based HBTs, leveraging the strengths of Ga₂O₃ and well-established semiconductor materials to drive advancements in high-power electronics.