First Demonstration of High-Performance Enhancement-Mode InAlGaN/GaN HEMTs on Silicon for Millimeter-Wave Applications with fT/fMAX of 71.5/173.1 GHz

An enhancement-mode recess-free InAlGaN/GaN HEMT on silicon is demonstrated for millimeter-wave RF applications by combining a polarization-engineered ultra-thin InAlGaN barrier with a high-quality LPCVD SiNₓ passivation stack. The strong polarization-induced channel charge enables positive threshold voltage (Vth) without gate recess, while the dense LPCVD SiNₓ effectively suppresses interface traps and gate leakage current. The proposed devices exhibit a high peak transconductance (gm) of 708 mS/mm and a gate leakage current (IGS) on the order of 10⁻¹⁰ A/mm. Small-signal measurements show a current-gain cutoff frequency (fT) of 71.5 GHz and a maximum oscillation frequency (fMAX) of 173.1 GHz under enhancement-mode operation. In addition, robust large-signal performance is achieved at 28 and 38 GHz, together with low noise figures across 24–45 GHz. These results establish the proposed recess-free GaN-on-Si HEMT as a scalable and RFIC-ready device platform for millimeter-wave front-end applications.