High performance vacuum annealed β-(Al_xGa_1−x)₂O₃/Ga₂O₃ HFET with f_T/f_MAX of 32/65 GHz

This letter reports high performance β - (Al_xGa_1−x)₂O₃/Ga₂O₃ Heterostructure FET (HFET) with an improved regrowth process and successful Al₂O₃ passivation. Highly scaled I shaped gates (100-200 nm L_G) have been fabricated with degenerately doped (N++) source/drain contact regrown by ozone molecular beam epitaxy (MBE). Aiming to address the limitations observed in previously reported devices, this work incorporates a low-power BCl₃/Ar and SF₆/Ar plasma etching process to remove the AlGaO barrier layer and Ga₂O₃ layer respectively before regrowth. Additionally, the surface was cleaned, and vacuum annealing was carried out before MBE regrowth to reduce any interface resistance between highly doped regrowth N++ and 2DEG layer. These meticulously designed fabrication steps enabled us to achieve the high DC current 0.5 A mm⁻¹ at 5 V drain bias with 6.1 Ω.mm on resistance (R_ON) at V_GS = 3 V, peak transconductance (g_m) of 110 mS mm⁻¹ at room temperature (V_DS = 15 V) and around 0.8 A mm⁻¹ (V_DS = 5 V) peak I_ON at low temperature (100 K). The current gain cut-off frequency (f_T) of 32 GHz and peak power gain cut-off frequency (f_MAX) of 65 GHz were extracted from radiofrequency (RF) measurements. The reported f_MAX is one of the highest for Ga₂O₃ based RF devices to the best of the authors’ knowledge. The f_T.L_G product was estimated to be 6.1 GHz-μm for 191 nm L_G and 32 GHz f_T, which is one of the highest reported among Ga₂O₃ devices. After passivating the device with thicker Al₂O₃, the device shows no current collapse demonstrating first time successful traps passivation with Al₂O₃ for β -Ga₂O₃ devices.