We elucidate a mechanism behind time-dependent on-state breakdown of GaN HEMTs, where the time-to-failure varies from sub-μs to hundreds of seconds. We reveal that the breakdown is sequentially caused by charge movement in the back barrier (BB), drain-corner electric field densification, impact ionization, and avalanche breakdown. Modeling of charge movement in the BB and impact ionization is key to predicting the on-state breakdown with TCAD.
