Investigating the Impact of Fe-Doped GaN and β-Ga₂O₃ Buffer Layers on a Laterally Scaled AlN/GaN HEMT Using Silicon Carbide Substrate for Next-Generation RF Electronics

The influence of gallium nitride (GaN) and beta-gallium oxide (β-Ga₂O₃) buffer layers on a laterally scaled AlN/GaN high-electron-mobility transistor (HEMT) using the emerging substrate material silicon carbide (SiC) was investigated in this work. We analyzed the direct-current/radio frequency (DC/RF) performance of AlN/GaN/GaN/AlN/SiC and novel AlN/GaN/β-Ga₂O₃/SiC HEMTs. Wide-bandgap (E_g = 4.7 eV) β-Ga₂O₃ material was used as a buffer. Due to the availability of bulk wafer size and low lattice mismatch with group III nitride alloys, β-Ga₂O₃ is a promising material for future GaN-based HEMT applications. The β-Ga₂O₃ acts as a natural back barrier, which mitigates buffer leakage current and leads to the confinement of more electrons in the GaN channel. Further, both devices were laterally scaled, and we report their DC/RF performance. The impact of Fe doping in the GaN buffer layer was also studied. The lattice mismatch of β-Ga₂O₃/SiC was 1.3%, and that for GaN/SiC was 6.4%, which requires the AlN layer as the nucleation layer to avoid stress and strain-related defects. This scaling shows a drastic impact and is also an indicator tool for improving overall device performance. The novel AlN/GaN/β-Ga₂O₃/SiC HEMT outperformed the alternatives, with a drain current (I_D) of 2.71 A/mm, transconductance (g_m) of 541 mS/mm, and cut-off frequency (f_T) of 391 GHz, with a gate length (L_G), gate-to-drain distance (L_GD), and gate-to–source distance (L_GS) of 50 nm, 0.8 µm, and 0.3 µm, respectively. There was an 18% increase in drain current (2.18 A/mm), 8% improvement in transconductance (503 mS/mm), and 6% improvement in cut-off frequency (373 GHz) when compared to a Fe-doped GaN buffer HEMT. Due to this outstanding performance, the proposed β-Ga₂O₃ buffer device paves the way for next-generation RF power applications.