Impacts of gate recess and passivation on AlGaN/GaN high electron mobility transistors

In this study, the impacts of gate recess and passivation on AlGaN/GaN high electron mobility transistors (HEMTs) were investigated. The trap-related characteristics were studied in detail by several different measurements including dc current-voltage, cur-rent collapse, gate lag, and flicker noise characterizations. With a Cl-2/Ar-recessed gate, drain current collapse factors (Delta I-max) of similar to 37.5 and similar to 6.9% were observed before and after SiN passivation. The gate lag measurements showed that the lagging phenomena almost disappear with SiN passivation for both Cl-2- and Cl-2/Ar-recessed devices. However, the flicker noise measurements revealed distinct noise levels of devices with different processes even after passivation. As the gate voltage (VG) changed from 2 to -4V, the devices recessed by Cl-2 exhibited lower drain noise current densities (S-ID/I-D(2) ranging from 2.8 x 10(-14) to 1.7 x 10(-12) Hz(-1) at 1 kHz) than those etched by Cl-2/Ar mixture gas (S-ID/I-D(2) ranging from 6.3 x 10(-14) to 6.0 x 10(-12) Hz(-1) at 1 kHz), whereas the devices without the recess process showed the lowest noise levels (S-ID/I-D(2) ranging from 2.8 x 10(-15) to 1.3 x 10(-13) Hz(-1) at 1 kHz). It was found that S-ID/I-D(2) increased monotonically when V-G changed from 2 to -4V. A bias dependence of the 1/f(gamma) slope gamma was observed, and a relatively large variation in the range of similar to 1.1 to 1.6 was found for devices recessed by Cl-2/Ar mixture gas. The number fluctuation model was employed to explain the observed trends. The results also indicated that the surface traps play an important role in these devices.