Thermal study of GaN-based HFET devices

The most important aspects of GaN-based devices are high breakdown field and high operating temperature. One highspeed device structure is the HFET (heterojunction field effect transistor) where two-dimensional electron gas (2DEG) is formed on AlGaN/GaN heterointerface. The electrons in 2DEG have significantly higher mobility than that in the conduction channel of a conventional metal-semiconductor field effect transistor (MESFET). Traditionally, GaN-based devices are fabricated on sapphire substrates. Since the sapphire substrate has relatively low thermal conductivity (0.28 W/cmK), it is necessary to carry out thermal analysis to ensure that the peak operating temperature of the device is within the acceptable range. Much effort has been exerted to provide sufficient thermal analysis in the past. In this paper, we present our thermal simulation using codes previously developed based on analytical solutions in our laboratory and compare the result of thermal simulation to actual thermal measurement results using nematic liquid crystal. Thermal simulation results agree reasonably well with measurement profiles.