Investigating the Current Collapse Mechanisms of p-GaN Gate HEMTs by Different Passivation Dielectrics

In this letter, the dynamic R
_on
degradation mechanisms of the p-GaN gate HEMTs induced by off-state stress are investigated with different passivation dielectrics AlON and SiN. The degradation mechanisms are twofold, including V
_TH
shift and surface trapping in the gate-to-drain access region, whose impacts are successfully distinguished. Surface trapping by SiN passivation is evidently proved to be the dominant factor that can almost induce a full current collapse. The V
_TH
positive shift diminishes the drain current by shrinking the overdrive V
_GS
, which however, can be compensated by a higher V
_GS
overdrive in applications. SiN passivation can effectively suppress the positive bias temperature instability effect, probably by passivating the p-GaN fast traps with hydrogen during passivation. Last, the transient measurements unveil that both the surface trapping and V
_TH
shift have a very slow recovery process.