Extreme Bandgap Recessed-Gate Metal Oxide Semiconductor Heterostructure Field Effect Transistors with Drain Current 0.28 A mm⁻¹ and Threshold Voltage −1.5 V

Herein, the first demonstration of hybrid high-k oxide (ZrO2-Al2O3) incorporation into extreme bandgap (EBG) Al0.87Ga0.13N/Al0.64Ga0.36N metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs) is presented, with both planar and recessed-gate designs on the same AlN/sapphire template with a state-of-the-art low contact resistance of 1.4 Ω mm (contact resistivity, ρc ≈ 5.7 × 10−6 Ω cm2). The recessed-gate MOSHFETs achieve a threshold voltage shift of ΔVTH = 5.8 V, highlighting improved channel control. Static output measurements reveal a peak drain current (IDS) of 340 mA mm−1 for the planar gate and 280 mA mm−1 for the recessed gate at VGS = +8 V, with corresponding on–off current ratios of ≈106 and ≈108. The recessed-gate structure demonstrates reduced gate leakage and minimal hysteresis, indicating robust fabrication processes with negligible impact on interface states. Transfer characteristics further show a peak transconductance (gm) of 31 and 45 mS mm−1 for the plain and recessed structures, respectively. These findings establish EBG recessed-gate MOSHFETs as a promising solution for advanced power devices requiring precise threshold voltage control, enhanced on-state current, and reduced leakage currents.