Fabrication and Characterization of Thin-Barrier $\hbox {Al}_{0.5}\hbox {Ga}_{0.5}\hbox {N/AlN/GaN}$ HEMTs

The growth, fabrication, and performance of Al_0.5Ga_0.5 N/AlN/GaN high-electron-mobility transistors (HEMTs) with a total barrier thickness of 7 nm are reported. An optimized surface passivation and an ohmic recess etch yield HEMTs exhibiting 0.72 S/mm peak extrinsic dc transconductance at a current density of 0.47 A/mm. Devices with a gate length of 90 nm achieve 78 GHz unity-current-gain frequency and up to 166 GHz maximum frequency of oscillation. The minimum noise figure at 10 GHz is 0.52 dB with an associated gain of 9.5 dB.