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

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.