Ultrathin InAlN/AlN Barrier HEMT With High Performance in Normally Off Operation

We present GaN-based high electron mobility transistors (HEMTs) with a 2-nm-thin InAlN/AlN barrier capped with highly dopedn⁺⁺GaN. Selective etching of the cap layer results in a well-controllable ultrathin barrier enhancement-mode device with a threshold voltage of$+$0.7 V. Then⁺⁺GaN layer provides a 290-Ω/sheet resistance in the HEMT access region and eliminates current dispersion measured by pulsed$IV$without requiring additional surface passivation. Devices with a gate length of 0.5-exhibit maximum drain current of 800 mA/mm, maximum transconductance of 400 mS/mm, and current cutoff frequencyfTof 33.7 GHz. In addition, we demonstrate depletion-mode devices on the same wafer, opening up perspectives for reproducible high-performance InAlN-based digital integrated circuits.