High‐frequency AlGaN/GaN HFETs with fT/fmax 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 (fT) and maximum oscillation frequency (fmax) were fabricated and characterised on SiC substrate. In the device, scaled source‐to‐drain distance (Lsd) 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 (gm) of 764 mS/mm was obtained in the AlGaN/GaN HFETs. Moreover, the maximum fT and fmax of the fabricated device reach to 149 and 263 GHz at the same bias, exhibiting a record‐high value of fT*fmax. This indicates that the AlGaN/GaN HFETs still have the potential for D‐band (110–170 GHz) power‐amplifier application with further optimisation. [ABSTRACT FROM AUTHOR]