p-capped GaN-AlGaN-GaN high-electron mobility transistors (HEMTs)

A novel p-capped GaN-AlGaN-GaN high-electron mobility transistor has been developed to minimize radio-frequency-to-dc (RF-DC) dispersion before passivation. The novel device uses a p-GaN cap layer to screen the channel from surface potential fluctuations. A low-power reactive ion etching gate recess combined with angle evaporation of the gate metal has been used to prevent gate extension and maintain breakdown voltage. Devices with gate lengths of 0.7 mum have been produced on sapphire. Current-gain cutoff frequencies (f(T)) of 20 GHz and maximum frequencies of oscillation (f(max)) of 38 GHz have been achieved. Unpassivated device demonstrated a saturated output power of 3.0 W/mm and peak power-added efficiency of 40% at 4.2 GHz (V-DS = +20 V).