Fabrication of 80-nm T-gate high indium In0.7Ga0.3As/In0.6Ga0.4As composite channels mHEMT on GaAs substrate with simple technological process**Project supported by the Key Laboratory of Nano-Devices and Applications, Nano-Fabrication Facility of SINANO, Chinese Academy of Sciences, the National Natural Science Foundation of China (Nos. 61274077, 61474031, 61464003), the Guangxi Natural Science Foundation (Nos. 2013GXNSFGA019003, 2013GXNSFAA019335), the National Basic Research Program of China

Abstract

An 80-nm gate length metamorphic high electron mobility transistor (mHEMT) on a GaAs substrate with high indium composite compound-channels In0.7Ga0.3 As/In0.6Ga0.4 As and an optimized grade buffer scheme is presented. High 2-DEG Hall mobility values of 10200 cm2/(V·s) and a sheet density of 3.5 × 1012 cm−2 at 300 K have been achieved. The device's T-shaped gate was made by utilizing a simple three layers electron beam resist, instead of employing a passivation layer for the T-share gate, which is beneficial to decreasing parasitic capacitance and parasitic resistance of the gate and simplifying the device manufacturing process. The ohmic contact resistance Rc is 0.2 ω·mm when using the same metal system with the gate (Pt/Ti/Pt/Au), which reduces the manufacturing cycle of the device. The mHEMT device demonstrates excellent DC and RF characteristics. The peak extrinsic transconductance of 1.1 S/mm and the maximum drain current density of 0.86 A/mm are obtained. The unity current gain cut-off frequency (fT) and the maximum oscillation frequency (fmax) are 246 and 301 GHz, respectively.