Influence of GaN- and Si₃N₄-Passivation Layers on the Performance of AlGaN/GaN Diodes With a Gated Edge Termination

摘要

This paper analyses the influence of the GaN and Si3N4 passivation (or "cap") layer on the top of the AlGaN barrier layer on the performance and reliability of Schottky barrier diodes with a gated edge termination (GET-SBDs). Both GaN cap and Si3N4 cap devices show similar dc characteristics but a higher density of traps at the SiO2/GaN interface or/and an increase of the total dielectric constant in the access region result in higher R-ON-dispersion in GaN cap devices. The leakage current at medium/low temperatures in both types of devices shows two low-voltage-independent activation energies, suggesting thermionic and field-emission processes to be responsible for the conduction. Furthermore, a voltage-dependent activation energy in the high-temperature range occurs from low voltages in the GaN cap devices and limits their breakdown voltage (V-BD). Time-dependent dielectric breakdown measurements show a tighter distribution in Si3N4 cap devices (Weibull slope beta = 3.3) compared to GaN cap devices (beta = 1.8). Additional measurements in plasma-enhanced atomic layer deposition (PEALD)-Si3N4 capacitors with different cap layers and T-CAD simulations show an electric field distribution with a strong peak within the PEALD-Si3N4 dielectric at the GET corner, which could accelerate the formation of a percolation path and provoke the device breakdown in GaN cap SBDs even at low-stress voltages.