Design of Beveled Edge Termination in GaN Vertical p-i-n Diodes: A Simulation Study

Various electric field profile simulations are carried to design the vertical gallium nitride (GaN) p-i-n diodes with negative beveled edge termination to optimize breakdown voltage. Although traditional beveled edge termination can also be used to alleviate the fringe electric field crowding effect and obtain a breakdown voltage comparable with the parallel plane ideal case, a larger length of the edge termination is required. In this paper, we introduced a two-step beveled edge termination structure to save the area used to improve the breakdown voltage, which can reduce 83% of the termination length required to achieve 90% of the ideal breakdown voltage. Through TCAD simulation, the higher doping concentration ratio between the P-GaN and the drift layer is, the shorter the depth of the mesa and the longer edge termination are needed to achieve the same percentage of the ideal breakdown voltage. The two-step beveled edge termination could save more area if the Mg concentration in P-GaN is larger. This structure and the rule explored in this paper has significance for the design of GaN-based p-i-n diodes with high breakdown voltage and small area.