Enhancement-mode Lg = 50 nm metamorphic InAlAs/InGaAs HEMTs on GaAs substrates with fmax surpassing 408 GHz

Abstract A novel self-aligned T-shaped gate enhancement-mode metamorphic In 0.50 Al 0.50 As/In 0.53 Ga 0.47 As HEMTs on GaAs substrates by MOCVD is proposed and demonstrated, utilizing an optimized multi-stage composite buffer scheme. High 2-D electron gas Hall mobility values of 9100 cm 2 /V s at 300 K and 38,900 cm 2 /V s at 77 K have been achieved. The mHEMT had a threshold voltage ( V th ) of +0.22 V, a maximum drain current of 786 mA/mm and transconductance up to 1.2 S/mm at V DS  = 0.5 V. The f T and f max of 50-nm T-shaped gate devices were 305 and 408 GHz, respectively. To the knowledge of the authors, these results are the highest reported for MOCVD-grown enhancement–mode mHEMTs on GaAs substrate.