High‐frequency AlGaN/GaN HFETs with f T / f max of 149/263 GHz for D‐band PA applications

Abstract

Scaled AlGaN/GaN heterostructure field-effect transistors (HFETs) with high unity current gain cut-off frequency (f T) and maximum oscillation frequency (f max) were fabricated and characterised on SiC substrate. In the device, scaled source-to-drain distance (L sd) of 600 nm was realised by employing non-alloyed regrown n+-GaN ohmic contacts. A 60 nm T-shaped AlGaN/GaN HFETs showed excellent DC and RF performance after gate recess. A record extrinsic transconductance (g m) of 764 mS/mm was obtained in the AlGaN/GaN HFETs. Moreover, the maximum f T and f max of the fabricated device reach to 149 and 263 GHz at the same bias, exhibiting a record-high value of f T*f max. This indicates that the AlGaN/GaN HFETs still have the potential for D-band (110–170 GHz) power-amplifier application with further optimisation.