Electric-Field Dependence of Junction Temperature in GaN HEMTs

Here we report junction temperature and thermal spreading in GaN HEMTs using a transient measurement technique that utilizes the thermionic Schottky gate characteristics to obtain temperatures. Our technique first calibrates the gate-to-source forward I-V characteristics of the device under test as a function of temperature by mounting on a chuck at a known temperature and under vacuum to eliminate heat loss effects. Thermal spreading measurements indicate a thermal resistance of ~25degC/W per mm between the two sensors located at -450mum and -225mum from the heater device.