High Efficiency Over 70% at 3.6-GHz InAlN/GaN HEMT Fabricated by Gate Recess and Oxidation Process for Low-Voltage RF Applications

In this work, high-efficiency InAlN/GaN high electron mobility transistor (HEMT) is fabricated by recess and oxidation process under the gate (RAO) for low-voltage RF applications. Compared with conventional HEMT fabricated on the same heterojunction, RAO-HEMT exhibits a significant decrease in gate leakage, attributed to the thin oxide layer formed around and under the gate as well as adjustment of the location of the peak electric field and confinement of the strong electric field in the oxide. Due to the alleviated electric field as well as adoption of
$\text{N}_{{2}}\text{O}$
for plasma treatment, suppressed RF dispersion including the extremely low current collapse and negligible knee voltage walkout is obtained for RAO-HEMT. Although RAO-HEMT delivers lower saturation current as the result of the partial oxidation of the barrier under the gate, it shows a similar ON-resistance to conventional HEMT, which contributes to the reduction in knee voltage. Besides, higher
${f}_{T}/{f}_{\text {MAX}}$
is achieved for RAO-HEMT, as the result of the higher dc transconductance and suppressed RF transconductance collapse as well as larger output resistance. Eventually, benefiting from the improvement in gate leakage, RF dispersion, knee voltage, and
${f}_{\text {MAX}}$
by RAO, RAO-HEMT delivers both higher power-added-efficiency (PAE) and output power (
${P}_{\text {OUT}}$
) than conventional HEMT. At 3.6 GHz, RAO-HEMT provides a high PAE of 71% (74%) at
${V}_{{\text {DS}}}$
of 6 V (9 V), which performs better than most of the existing Si, GaAs, or GaN RF devices in PAE, revealing the great potential of InAlN/GaN RAO-HEMT in low-voltage low-power consumption RF applications.