Evolution of field dependent carrier trapping during off-state degradation for GaN based metal oxide semiconductor high electron mobility transistors

Abstract

We have shown that the off-state degradation in GaN based metal-oxide-semiconductor high electron mobility transistors has three field dependent regimes. We have considered Al2O3 and AlOxNy as the gate dielectrics. The degradation is dominated by electron trapping near the drain edge at relatively low electric field; hole trapping followed by structural defects tends to dominate at high electric field. The structural defects may potentially be caused by an inverse piezoelectric effect when the AlGaN/GaN interface may relax partially. The hole trapping, in particular, at moderate to high electric field can lead to an anomalous trend. The off-state drain current bears the signature of the degradation. The transistor performance is found to deteriorate for all the cases independent of the degradation mechanism. The trapping contribution toward the degradation is partially recoverable; however, the structural damage is found to be permanent. It is also observed that both the gate dielectrics qualitatively suffer from the same degradation mechanism with oxynitride high electron mobility transistors showing higher resilience than their oxide counterpart.

Off-State Degradation and Recovery in Oxide/AlGaN/GaN Heterointerfaces: Importance of Band Offset, Electron, and Hole Trapping

“…The off-state degradation has been studied prevalently for atomic layer-deposited (ALD) Al 2 O 3 and SiN/AlGaN/GaN HEMTs where bulk trapping of electrons injected from the gate is found to be the critical mechanism for device degradation . It is also proposed that the creation of unrecoverable defect states below the gate region and localized state formation at large electric fields in the AlGaN barrier region lead to permanent degradation and eventual breakdown of these devices. At very high voltages, the inverse piezoelectric effect is stated to be the fundamental reason for the permanent breakdown of the devices …”