Time-Dependent Breakdown Mechanisms and Reliability Improvement in Edge Terminated AlGaN/GaN Schottky Diodes Under HTRB Tests

In this letter, we investigate the time-dependent breakdown mechanisms in edge terminated AlGaN/GaN lateral Schottky diodes under high-temperature reverse bias (HTRB) tests. Thanks to a combined experimental/simulation analysis, we ascribe the device failure to two distinct time-sequential breakdown mechanisms caused by a localized electric field peak at the edge termination corner. In particular, the combined effect of high electric field and temperature causes a first breakdown of the plasma-enhanced atomic layer deposition (PEALD)-Si3N4 followed by a second one in the AlGaN barrier. To validate this hypothesis, a 2-D TCAD simulator was used, and the breakdown path in Si3N4 was modeled by an inclusion of a narrow metal filament. The electrical simulations well reproduce the characteristics of the fresh and degraded GaN diodes. Finally, we demonstrate that the diode reliability under HTRB tests can be significantly improved by using a metalorganic chemical vapor deposition (MOCVD)-Si3N4 dielectric in the edge termination. This reliability improvement is related to a better material quality of MOCVD-Si3N4, showing a higher breakdown field compared with the PEALD-Si3N4.