610 GHz InAlAs/In0.75GaAs Metamorphic HEMTs with an Ultra-Short 15-nm-Gate

Ultra-short-gate InAlAs/InGaAs high electron mobility transistors (HEMTs) have been successfully fabricated with nano-gate fabrication technology and epitaxial optimization. We obtained an extrinsic maximum transconductance (G_m,max) of 1.65 S/mm and a current gain cutoff frequency (f_T) of 610 GHz for 15-nm-gate HEMTs on GaAs substrates. Through a delay time analysis, the ultrahigh f_T of this work is explained by an enhanced average electron velocity under the gate (V_ave) of 4.3 x 10⁷ cm/s, which was a result of reduction of gate length (L_g) and epitaxial engineering. This report is the first experimental demonstration of 15 nm InAlAs/TnGaAs metamorphic HEMTs (MHEMTs) with an extremely high f_T of 610 GHz.