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 Cl2/Ar-recessed gate, drain current collapse factors ( Imax) 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 Cl2and Cl2/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 Cl2 exhibited lower drain noise current densities (SID=ID ranging from 2:8 10 14 to 1:7 10 12 Hz 1 at 1 kHz) than those etched by Cl2/Ar mixture gas (SID=ID 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 (SID=ID 2 ranging from 2:8 10 15 to 1:3 10 13 Hz 1 at 1 kHz). It was found that SID=ID increased monotonically when VG changed from 2 to 4V. A bias dependence of the 1= f slope was observed, and a relatively large variation in the range of 1:1 to 1.6 was found for devices recessed by Cl2/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. [DOI: 10.1143/JJAP.46.478]