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 (ZrO 2 ‐Al 2 O 3 ) incorporation into extreme bandgap (EBG) Al 0.87 Ga 0.13 N/Al 0.64 Ga 0.36 N 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, ρ c ≈ 5.7 × 10 −6 Ω cm 2 ). The recessed‐gate MOSHFETs achieve a threshold voltage shift of Δ V TH = 5.8 V, highlighting improved channel control. Static output measurements reveal a peak drain current ( I DS ) of 340 mA mm −1 for the planar gate and 280 mA mm −1 for the recessed gate at V GS = +8 V, with corresponding on–off current ratios of ≈10 6 and ≈10 8 . 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 ( g m ) 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.