AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs) with 4 nm thick Al 2 O 3 gate oxide were prepared and their performance was compared with that of AlGaN/GaN HFETs. The MOSHFETs yielded ∼40% increase of the saturation drain current compared with the HFETs, which is larger than expected due to the gate oxide passivation. Despite a larger gate-channel separation in the MOSHFETs, a higher extrinsic transconductance than that of the HFETs was measured. The drift mobility of the MOSHFETs, evaluated on large-gate FET structures, was significantly higher than that of the HFETs. The zero-bias mobility for MOSHFETs and HFETs was 1950 cm 2 V -1 s -1 and 1630 cm 2 V -1 s -1 , respectively. These features indicate an increase of the drift velocity and/or a decrease of the parasitic series resistance in the MOSHFETs. The current collapse, evaluated from pulsed I−V measurements, was highly suppressed in the MOSHFETs with 4 nm thick Al 2 O 3 gate oxide. This result, together with the suppressed frequency dispersion of the capacitance, indicates that the density of traps in the Al 2 O 3 /AlGaN/GaN MOSHFETs was significantly reduced.

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