Comparison of SiNx and AlN Passivations for AlGaN/GaN Hemts

Abstract

We present a comparative study of suppressing AlGaN/GaN HEMTs’ current collapse by two types of passivation materials: amorphous SiNx (grown by PECVD and LPCVD) and epitaxial AlN (grown by plasma enhanced atomic layer deposition (PEALD). The motivation of this study stems from the different mechanisms underlying the two passivation techniques, namely, surface-charge-compensation by shallow donors (with SiNx) and polarization charge (with epitaxial AlN). Since de-trapping from the shallow donor levels is a time-dependent process and the polarization charge compensation is a time-indepdent phenomenon, AlN-passivated AlGaN/GaN HEMTs was found to exhibit improved dynamic switching behavior than SiNx-passivated devices. The results show that the depletion region is much narrower in AlN-passivated devices than SiNx-passivated and un-passivated devices. The transient characteristics reveal the superiority of AlN passivation as the formation of depletion region is predominantly a field effect while the de-trapping from the shallow donor levels in SiNx-passivated devices is limited by their intrinsic time constant. AlN-passivated devices show much smaller dynamic RON variation under both fast and slow switching operations.