Origin of physical degradation in AlGaN/GaN on Si high electron mobility transistors under reverse bias stressing

We have investigated the role of threading dislocations in pit formation during stressing of AlGaN/GaN on Si high electron mobility transistors under high reverse bias. Upon stressing, the drain current saturation (I_D-saturation) decreases over time. The amount of I_D-saturation degradation correlates well with pit formation at the gate-edge, where the electric field is the highest. Using a transmission electron microscope weak-beam technique, it is found that pits tend to nucleate at threading dislocations that have a screw component, even when these dislocations are at locations away from the gate-edge. An explanation based on an electrochemical oxidation model is proposed.