AbstractThis work describes a study regarding the SiO2/Si3N4 passivation layer thickness effect on the Au/Mo/ Al0.25Ga0.75N/GaN/Si (111) rectifier contact behaviour. Two total different thicknesses of SiO2/Si3N4dielectric are deposited on AlGaN/GaN with different residual stress which modify the stress in the AlGaN barrier under the gate. The defects occuring at the dielectric/AlGaN interface are characterized using the photoluminescence technique. I‐V characteristics of both Schottky contacts show that the thicker passivation change the Schottky contact behaviour and permit to reduce significantly the density of interface traps involving a drop of the Schottky leakage current of several order of magnitude. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)