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, current collapse, gate lag, and flicker noise characterizations. With a Cl 2 /Ar-recessed gate, drain current collapse factors (Δ I max ) of ∼37.5 and ∼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 ( V G ) changed from 2 to -4 V, the devices recessed by Cl 2 exhibited lower drain noise current densities ( S ID / I D 2 ranging from 2.8 × 10 -14 to 1.7 × 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 × 10 -14 to 6.0 × 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 × 10 -15 to 1.3 × 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 -4 V. A bias dependence of the 1/ f γ slope γ was observed, and a relatively large variation in the range of ∼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.