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

• mHEMT was grown utilizing a novel multi-stage composite buffer scheme.
• Lg = 50 nm T-shaped gate enhancement-mode mHEMT device was fabricated successfully.
• The fT and fmax of 50-nm T-shaped gate devices were 305 and 408 GHz.
• Highest reported for MOCVD-grown enhancement-mode mHEMTs on GaAs substrate.

A novel self-aligned T-shaped gate enhancement-mode metamorphic In0.50Al0.50As/In0.53Ga0.47As 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 cm2/V s at 300 K and 38,900 cm2/V s at 77 K have been achieved. The mHEMT had a threshold voltage (Vth) of +0.22 V, a maximum drain current of 786 mA/mm and transconductance up to 1.2 S/mm at VDS = 0.5 V. The fT and fmax 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.