We report on SiO 2 / AlGaN / GaN metal-oxide-semiconductor heterostructure field-effect transistors ͑MOSHFETs͒, which exhibit a 6.7 W / mm power density at 7 GHz. Unpassivated and SiO 2-passivated heterostructure field-effect transistors ͑HFETs͒ were also investigated for comparison. Deposited 12 nm thick SiO 2 yielded an increase of the sheet carrier density from 7.6ϫ 10 12 to 9.2ϫ 10 12 cm −2 and a subsequent increase of the static drain saturation current from 0.75 to 1.09 A / mm. The small-signal rf characterization of the MOSHFETs showed an extrinsic current gain cutoff frequency f T of 24 GHz and a maximum frequency of oscillation f max of 40 GHz. The output power of 6.7 W / mm of the MOSHFETs measured at 7 GHz is about two times larger than that of HFETs. The results obtained demonstrate the suitability of GaN-based MOSHFETs for high-power electronics.

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In this comparative study we investigate AlGaN/GaN‐based unpassivated and passivated HFETs and MOSHFETs with regards to DC‐, RF‐, and power‐performance. For optimal comparability, all devices emanate from the same wafer consisting of a SiC‐substrate, a 3 µm GaN‐ and a 30 nm Al0.28Ga0.72N‐layer. Devices are processed simultaneously to a large extend. Passivated devices are coated with a 10 nm thick SiO2‐layer between the electrodes, MOSHFETs contain a 10 nm thick SiO2‐layer serving as gate‐insulator underneath the gate and as conventional passivation‐layer between the electrodes. Unpassivated devices serve as reference. We present empirical evidence that MOSHFETs outperform both the conventional and the passivated HFETs with respect to DC‐, RF‐, and power‐performance, and we point out the different mechanisms responsible for the behaviour of the devices. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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