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Abstract Breakdown voltage (BV) is arguably one of the most critical parameters for power devices. While avalanche breakdown is prevailing in silicon and silicon carbide devices, it is lacking in many wide bandgap (WBG) and ultra-wide bandgap (UWBG) devices, such as the gallium nitride high electron mobility transistor and existing UWBG devices, due to the deployment of junction-less device structures or the inherent material challenges of forming p-n junctions. This paper starts with a survey of avalanche and non-avalanche breakdown mechanisms in WBG and UWBG devices, followed by the distinction between the static and dynamic BV. Various BV characterization methods, including the static and pulse I – V sweep, unclamped and clamped inductive switching, as well as continuous overvoltage switching, are comparatively introduced. The device physics behind the time- and frequency-dependent BV as well as the enabling device structures for avalanche breakdown are also discussed. The paper concludes by identifying research gaps for understanding the breakdown of WBG and UWBG power devices. 

This work demonstrates a novel junction termination extension (JTE) with a graded charge profile for vertical GaN p-n diodes. The fabrication of this JTE obviates GaN etch and requires only a single-step implantation. A bi-layer photoresist is used to produce an ultra-small bevel angle (~0.1°) at the sidewall of a dielectric layer. This tapered dielectric layer is then used as the implantation mask to produce a graded charge profile in p-GaN. The fabricated GaN p-n diodes show a breakdown voltage ( BV ) of 1.7 kV (83% of the parallel-plane limit) with positive temperature coefficient, as well as a high avalanche current density over 1100 A/cm 2 at BV in the unclamped inductive switching test. This robust avalanche is ascribed to the migration of the major impact ionization location from the JTE edge to the main junction. This single-implant, efficient, avalanche-capable JTE can potentially become a building block of many vertical GaN devices, and its fabrication technique has wide device and material applicability. 

Power devices are highly desirable to possess excellent avalanche and short-circuit (or surge-current) robustness for numerous power electronics applications like automotive powertrains, electric grids, motor drives, among many others. Current commercial GaN power device, the lateral GaN high-electron-mobility transistor (HEMT), is known to have no avalanche capability and very limited short-circuit robustness. These limitations have become a roadblock for penetration of GaN devices in many industrial power applications. Recently, through collaborations with NexGen Power Systems (NexGen), Inc., we have demonstrated breakthrough avalanche, surge-current and short-circuit robustness in NexGen’s vertical GaN p-n diodes and fin-shape junction-gate field-effect-transistors (Fin-JFETs). These large-area GaN diodes and Fin-JFETs were manufactured in NexGen’s 100 mm GaN-on-GaN fab. The demonstrated avalanche, surge-current and short-circuit capabilities are comparable or even superior to Si and SiC power devices. Additionally, vertical GaN Fin-JFETs were found to fail to open-circuit under avalanche and short-circuit conditions, which is highly desirable for the system safety. This talk reviews the key robustness results of vertical GaN power devices and unveils the enabling device physics. Fundamentally, these results signify that, in contrast to some popular belief, GaN devices with appropriate designs can achieve excellent robustness and thereby encounter no barriers for applications in electric vehicles, grids, renewable processing, and industrial motor drives.