Impact of drain electrode shape irregularities on breakdown voltage of AlGaN/GaN HEMTs

In this work, we investigated the effect of shape irregularities of drain electrode on the breakdown voltage of AlGaN/GaN HEMTs. We found that some random devices having rough metal edge definition tend to have lower breakdown voltages. In addition, these devices showed localized high intensity luminescence observed under near pinch-off condition. This is likely due to electric field concentration near irregularities such as sharp edges and corners that were randomly formed at some point during device fabrication. On the other hand, devices that have smooth metal edge definition exhibited uniform faint electroluminescence along the drain electrode edge. We also fabricated AlGaN/GaN HEMTs with intentionally-designed patterns such as sawtooth profiles along the drain edge. Intense luminescence localized at the apexes of sawtooth pattern together with the relatively lower breakdown voltages of these devices confirmed the importance of maintaining smooth drain electrode edge definition for achieving high breakdown performance in AlGaN/GaN HEMTs.