Transient Thermoreflectance for Gate Temperature Assessment in Pulse Operated GaN-Based HEMTs

An experimental method to measure the gate metal temperature of GaN-based high electron mobility transistors is demonstrated. The technique is based on transient thermoreflectance measurements performed from the backside of the device. The thermoreflectance coefficient of the gate metal was calibrated by correlating the relative change of its optical reflectivity with the temperature change measured in the GaN layer using time-resolved Raman thermography during the device cooling transient. Simulated temperature transients were in good agreement with the experimental data. The main advantage of this new method is that it enables the direct assessment of gate metal temperature under device pulsed operation regardless of the device design.