Abstract
Depletion-mode high-electron-mobility transistors (HEMTs) with an 11 nm quaternary In0.13Al0.83Ga0.04N barrier and a 5 nm In0.05Ga0.95N channel on SiC substrates have been fabricated. The as-processed HEMT structure features a channel electron density of 2.08×1013 cm-2 and a mobility of 1140 cm2 V-1 s-1. A device with a 50-nm-long T-shaped gate shows a maximum output current density of 2.0 A/mm, a peak extrinsic DC transconductance of 690 mS/mm, and cut-off frequencies fT/fmax of 260/220 GHz at the same bias, representing a record high √fT·fmax of 239 GHz for InGaN channel HEMTs.