220-GHz Quaternary Barrier InAlGaN/AlN/GaN HEMTs

Depletion-mode high-electron mobility transistors (HEMTs) based on a quaternary barrier In0.13Al0.83Ga0.04 N/AlN/GaN heterostructure 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 frequency f(T) of 220 GHz for quaternary barrier GaN-based HEMTs, which is also among the highest f(T) for all GaN-based HEMTs. The large L-g . f(T) product of 14.5 GHz . mu m with a gate-length-to-barrier-thickness aspect ratio of 5.8 indicates a high effective electron velocity of 0.9 x 10(7) cm/s, attributed to a high electron Hall mobility (1790 cm(2)/V . s at an n(s) of 1.8 x 10(13) cm(-2))-the highest reported in GaN-channel HEMTs with In-containing barriers. An intrinsic electron velocity of 1.7 x 10(7) cm/s, extracted from conventional Moll delay-time analysis, is comparable to that reported in the state-of-art AlGaN/GaN HEMTs.