RF operation of AlN/Al0.25Ga0.75N/AlN HEMTs with fT/fmaxof 67/166 GHz

We report on highly-scaled Al0.25Ga0.75N channel high electron mobility transistors. Regrown ohmic contacts covering the sidewall of the compressively strained Al0.25Ga0.75N channel exhibited a low contact resistance of Rc= 0.23 Ω · mm. Scaled devices with a T-shaped gate showed record high speed for any AlGaN-based transistors, fT/fmax= 67/166 GHz, while simultaneously achieving high average breakdown field exceeding 2 MV cm−1. The load-pull measurements performed at 10 GHz revealed a 20% peak power added efficiency with an output power density of 2 W mm−1, which is mainly limited by the RF dispersion.