Breaking the p-type doping barrier in β-Ga₂O₃: a GaN-based heterojunction bipolar transistor with high gain, high breakdown, and RF capability

Despite extensive research on unipolar β-Ga₂O₃ semiconductor devices, the advancement of bipolar devices, particularly heterojunction bipolar transistors (HBTs), has been significantly hindered by the lack of reliable p-type doping in β-Ga₂O₃. In this paper, we present the first comprehensive simulation study of a functional HBT based on an n-type β-Ga₂O₃ emitter, a p-type GaN base, and an n-type GaN collector, aiming to address the critical challenge of p-type doping in β-Ga₂O₃ for bipolar devices. The proposed Ga₂O₃/GaN HBT, simulated with full consideration of traps, exhibits a maximum DC current gain (<i>β</i> _DC) of 18.3, a high collector current density (<i>J</i> _C) of 14.3 kA cm^-2, a collector-base breakdown voltage (BV_CBO) of 120 V, a power figure of merit (PFOM) of 41.3 MW cm^-2, and a low specific on-resistance (<i>R</i> _on,sp) of 0.35 mΩ cm². The temperature-dependent current-voltage (<i>I</i>-<i>V</i>) characteristics from 300 K to 460 K reveal stable operation up to 460 K, albeit with a 31.1% reduction in <i>β</i> _DC and a 30.0% decline in PFOM due to carrier mobility degradation and enhanced recombination. Furthermore, device performance was optimized by engineering the base and collector thicknesses. The results indicate that a thin base (0.05 μm) maximizes <i>β</i> _DC, while a thick collector (2.0 μm) boosts PFOM to 138 MW cm^-2 without compromising gain. In addition, high-frequency simulations show a cutoff frequency (<i>f</i> _T) of 30 GHz at 300 K, confirming the device's suitability for RF and power-switching applications. These results indicate that the Ga₂O₃/GaN HBT is a promising candidate for next-generation power electronics, owing to its unique combination of high breakdown voltage and excellent frequency performance.