RF Performance of Deep-Recessed N-Polar GaN MIS-HEMTs Using a Selective Etch Technology Without Ex Situ Surface Passivation

We present a deep-recessed nitrogen-polar AlGaN/GaN MIS-HEMT employing a V-gate structure recessed through a thick GaN cap to prevent dc-to-RF dispersion. A process for selectively dry etching N-polar GaN over AlGaN has been established to achieve repeatable etch depth for the gate recess. Devices with a drawn gate length of 0.7- μm showed a current-gain cutoff frequency (
fT
) of 15 GHz and a power-gain cutoff frequency (
fmax
) of 42 GHz. A continuous-wave output power density of 5.5 W/mm was measured at 4 GHz, with a record associated power-added efficiency of 74% and a large-signal gain of 14.5 dB at a drain bias of 24 V.