220-GHz Quaternary Barrier InAlGaN/AlN/GaN HEMTs

Depletion-mode high-electron mobility transistors (HEMTs) based on a quaternary barrierIn0.13Al0.83Ga0.04/AlN/GaNheterostructure on SiC substrate were fabricated. The 66-nm-long gate device shows a dc drain current density of 2.1 A/mm, a peak extrinsic transconductance of 548 mS/mm, and a record current gain cutoff frequencyfTof 220 GHz for quaternary barrier GaN-based HEMTs, which is also among the highestfTfor all GaN-based HEMTs. The largeLg · fTproduct of 14.5GHz ·with a gate-length-to-barrier-thickness aspect ratio of 5.8 indicates a high effective electron velocity of0.9 × 10⁷\ cm/s, attributed to a high electron Hall mobility (1790cm²/V · sat annₛof1.8 × 10¹³\ cm⁻²)—the highest reported in GaN-channel HEMTs with In-containing barriers. An intrinsic electron velocity of1.7 × 10⁷\ cm/s, extracted from conventional Moll delay-time analysis, is comparable to that reported in the state-of-art AlGaN/GaN HEMTs.