Thermoreflectance CCD imaging of self heating in AlGaN/GaN high electron mobility power transistors at high drain voltage

Thermoreflectance CCD imaging with sub-micron spatial resolution was used to characterize self heating nonuniformity in two finger AlGaN/GaN high electron mobility power transistors at equivalent power (1.27 W) for different combinations of drain and gate voltage. Thermoreflectance images of device surface temperature revealed formation and redistribution of local hotspots as transistor drain voltage increased from V_D=10.7 V to 50 V. For all bias points, heating between the two fingers was not fully uniform. At high drain voltage, heating migrated toward the drain side of the channel and increased thermal nonuniformity was observed along symmetric drain and source fingers. Direct microthermocouple measurements confirmed the spatial temperature nonuniformity that was observed in thermoreflectance images. Results demonstrated the usefulness of fast thermoreflectance imaging to inspect self heating in GaN thin film power devices with high with high spatial resolution.