Tri-Gate Normally-Off AlN/GaN HEMTs With 2.36 W/mm of Power Density and 67.5% Power-Added-Efficiency at V_d = 12 V

In this letter, we present high-performance tri-gate normally-off HEMTs RF power devices using MOCVD-grown thin barrier SiN/AlN/GaN heterostructures. The normally-off devices exhibit alloyed Ohmic contact resistance of about $0.35 \Omega \cdot $ mm, low threshold-voltage of 0.2 V, very high output current of 1.61 A/mm, and high peak power added efficiency (PAE) of 67.5% with drain voltage ${(}{V}_{\text {d}}{)}$ of 12 V and frequency at 3.6 GHz. Owing to the high breakdown voltage of 159 V when gate bias at −4 V, the normally-off device shows a maximum output power of 5.96 W/mm at ${V}_{\text {d}}$ = 28 V with a peak PAE of over 50% and gain of over 20 dB. The SiN/AlN/GaN epi-structures and tri-gate normally-off HEMTs demonstrated in this work show promising potential for both low-voltage and high-voltage applications.