New source-side breakdown mechanism in AlGaN/GaN insulated-gate HEMTs

We find that off-state breakdown in AlGaN/GaN insulated-gate HEMTs can occur at the source-side of the gate with increase in the drain voltage. This new finding is borne out by extensive electrical measurements and confirmed with the OBIRCH (Optical Beam Induced Resistance CHange) technique. It is explained by a hypothesis whereby holes generated at high Vds flow to the source-side of the gate, and due to the low valence band offset, enter the gate insulator and damage it. Holes also cause threshold voltage shifts that turn the device on. The damage occurs in discrete spots, as would be expected by defects. Finally, we show improved breakdown voltage with a better gate-dielectric interface.