Record 34.2% efficient mm‐wave N‐polar AlGaN/GaN MISHEMT at 87 GHz

A novel device technology has been developed to enable the fabrication of high performance mm‐wave GaN high electron mobility transistors (HEMTs) for solid‐state power amplifiers operating in W‐band. By utilising the reverse polarisation of N‐polar GaN, an in‐situ GaN cap layer added in the device access regions acts to improve the channel conductivity and reduces the impact of surface states on device performance. A low dispersion HEMT with 149 GHz peak f T and 285 GHz peak f max demonstrated simultaneous high efficiency and output power density with 34.2% peak power‐added efficiency and an associated 2.5 W/mm output power at 87 GHz.