A new electro-optical transmission-line measurement-method revealing a possible contribution of source and drain contact resistances to GaN HEMT dynamic on-resistance

Despite their potential in the field of power electronics, many reliability issues still affect the electrical performance of Gallium Nitride HEMT power devices and require an effort of analysis and understanding. The characterization of the on-state resistance of this transistor is necessary to understand the dynamics of some phenomena such as trapping. The degradation of this resistance has always been related to traps in the 2DEG channel, without taking into consideration possible contributions from the source and drain contacts (metal/semiconductor). In this work, resistance measurements, with and without ultra-violet illumination, are performed on three different technological options to highlight the effect of illumination on contact resistances. •Variation of the contact resistance with an optical excitation in a GaN HEMT•This was observed on two technological options but not on a third one.•About 30% of the total resistance variation is attributed to contact resistance.•The illumination effect on the contact resistance was related to the epitaxy.