Normally-Off AlGaN/GaN Heterojunction Metal-Insulator-Semiconductor Field-Effect Transistors With Gate-First Process

In this letter, AlGaN/GaN heterojunction metal-insulator-semiconductor field-effect transistors with gate-first process were developed for normally-off operation with p-GaN cap layers and SiN
_x
dielectrics. To avoid the effect of the annealing process on the gate, a low-temperature ohmic contact technique was developed at an annealing temperature of about 500 °C for 20 min in N
₂
ambient. With the assistance of inductively coupled plasma dry etching, a contact resistance of 1.45 Ω · mm and sheet resistance of 1080.1 Ω/□ were obtained in the recessed region. Owing to the inset of the SiNx layer, the threshold voltage of the fabricated device was enhanced to approximately 2 V, and good pinch-off was observed with the gate voltage up to 16 V. Compared with the conventional high-temperature ohmic annealing process, the gate leakage current was suppressed significantly in both reverse and forward directions. Good device performance was confirmed with a maximum channel electron field-effect mobility of 1500 cm
²
V
^-1
s
^-1
.