Fast transient thermoreflectance CCD imaging of pulsed self heating in AlGaN/GaN power transistors

Pulsed thermoreflectance CCD imaging with submicron spatial resolution and 50 millikelvin temperature resolution is used to study fast transient heating in gallium nitride high electron mobility power transistors (GaN HEMTs) on silicon carbide substrate. Transient surface temperature distribution is measured between 50 ns and 100 μs for pulsed power to 19 W/mm. Time evolution of surface temperature for different HEMT regions is analyzed. Significant variation is observed between the thermal rise times for the gate metal, GaN channel, and drain metal. Steady state temperature rise of 68°C on the drain contact metal is reached at 100 μs at 19 W/mm. Observation of time varying thermal gradients in critical HEMT features under fast pulsed operation may help understanding of reliability and failure mechanisms in GaN power transistors.