547-GHz ft In0.7Ga0.3As-In0.52Al0.48As HEMTs with reduced source and drain resistance

We fabricated 30-nm gate pseudomorphic channel In_0.7Ga_0.3As-In_0.52Al_0.48As high electron mobility transistors (HEMTs) with reduced source and drain parasitic resistances. A multilayer cap structure consisting of Si highly doped n⁺-InGaAs and n⁺-InP layers was used to reduce these resistances while enabling reproducible 30-nm gate process. The HEMTs also had a laterally scaled gate-recess that effectively enhanced electron velocity, and an adequately long gate-channel distance of 12nm to suppress gate leakage current. The transconductance (g_m) reached 1.5 S/mm, and the off-state breakdown voltage (BV_gd) defined at a gate current of -1 mA/mm was -3.0 V. An extremely high current gain cutoff frequency (f_t) of 547 GHz and a simultaneous maximum oscillation frequency (f_max) of 400 GHz were achieved: the best performance yet reported for any transistor.