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.

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Dislocations are known to be associated with both physical and electrical degradation mechanisms of AlGaN/GaN-on-Si high electron mobility transistors (HEMTs). We have observed threading dislocation movement toward the gate-edges in AlGaN/GaN-on-Si HEMT under high reverse bias stressing. Stressed devices have higher threading dislocation densities (i.e. ∼5 × 109/cm2) at the gate-edges, as compared to unstressed devices (i.e. ∼2.5 × 109/cm2). Dislocation movement correlates well with high tensile stress (∼1.6 GPa) at the gate-edges, as seen from inverse piezoelectric calculations and x-ray synchrotron diffraction residual stress measurements. Based on Peierls stress calculation, we believe that threading dislocations move via glide in 〈112¯0〉/{11¯00} and 〈112¯0〉/{11¯01} slip systems. This result illustrates the importance of threading dislocation mobility in controlling the reliability of AlGaN/GaN-on-Si HEMTs.

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