220-GHz Quaternary Barrier InAlGaN/AlN/GaN HEMTs

Depletion-mode high-electron mobility transistors (HEMTs) based on a quaternary barrier In_0.13Al_0.83Ga_0.04 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 ·μm with a gate-length-to-barrier-thickness aspect ratio of 5.8 indicates a high effective electron velocity of 0.9 ×10⁷ cm/s, attributed to a high electron Hall mobility (1790 cm²/V ·s at an n_s of 1.8 ×10^13-2)-the highest reported in GaN-channel HEMTs with In-containing barriers. An intrinsic electron velocity of 1.7 ×10⁷ cm/s, extracted from conventional Moll delay-time analysis, is comparable to that reported in the state-of-art AlGaN/GaN HEMTs.