Understanding the Leakage Mechanisms and Breakdown Limits of Vertical GaN-on-Si p+n-n Diodes: The Road to Reliable Vertical MOSFETs

This work investigates p+n-n GaN-on-Si vertical structures, through dedicated measurements and TCAD simulations, with the ultimate goal of identifying possible strategies for leakage and breakdown optimization. First, the dominant leakage processes were identified through temperaturedependent current–voltage characterization. Second, the breakdown voltage of the diodes was modelled through TCAD simulations based on the incomplete ionization of Mg in the p+ GaN layer. Finally, the developed simulation model was utilized to estimate the impact of varying the p-doping concentration on the design of breakdown voltage; while high p-doped structures are limited by the critical electric field at the interface, low p-doping designs need to contend with possible depletion of the entire p-GaN region and the consequent punch-through. A trade-off on the value of p-doping therefore exists to optimize the breakdown.This research activity was partly funded by project "Novel vertical GaN-devices for next generation power conversion", NoveGaN (University of Padova), through the STARS CoG Grants call. Part of this work was supported by MIUR (Italian Minister for Education) under the initiative "Departments of Excellence" (Law 232/2016)