On the origin of off-state leakage current in n-p-n vertical structures for GaN-based trench-MOSFETs

In this work, we present the results of research on the off-current mechanism in vertical trench MOS devices manufactured on an ammonothermal substrate. Transistors and npn diode test structures were characterized electrically as well as by SEM and by AFM, which results compared to CAD simulations. We demonstrate that while Mg reactivation is a high-temperature process that enhances the ability to block high voltages, it also introduces killer defects that can degenerate structures. Additionally, we observed that the leakage current at the edges of the mesa has minimal significance. The findings highlight that substrate quality is a crucial factor in preventing killer defect formation and likely in minimizing leakage current at the npn epitaxial stack and off-current in transistor devices.