Reactive evaporation of SiOx films for passivation of GaN high-electron-mobility transistors

Abstract

The surface passivation effects of silicon suboxide (SiOx) prepared by the reactive evaporation of silicon monoxide in oxygen atmosphere on the performance of AlGaN/AlN/GaN high-electron-mobility transistors (HEMTs) have been investigated. SiOx films with different oxygen contents (1.10 ≤ x ≤ 1.71) and root-mean-square (RMS) roughnesses (0.55 ≤ RMS ≤ 1.01 nm) were prepared under residual pressures from 1 × 10−6 to 6 × 10−4 Torr. Hall measurements revealed obvious increases in the product of sheet carrier concentration and electron mobility after the passivation. Accordingly, increases in drain current and transconductance were observed for all the SiOx passivated HEMTs. Both the gate and drain leakage currents first decreased and then increased with the increase of oxygen content. The lowest gate leakage current was observed in the devices with SiO1.23 passivation, and it was almost 20 times lower than that of the unpassivated devices. The same devices also exhibited the lowest current collapse and off-state drain current. The variations in leakage currents as a function of the residual pressure were found to correlate with the surface roughness of the passivation layer. Finally, the breakdown voltage of the SiO1.23 passivated HEMTs increased to 151 V, up from 99 V in unpassivated devices.