Self-heating in high-power AlGaN-GaN HFETs

We compare self-heating effects in AlGaN-GaN heterostructure field effect transistors (HFETs) grown on sapphire and SiC substrates. Heat dissipation strongly affects the device characteristics soon after the application of the source-drain voltage (in less than 10/sup -7/ s). Our results show that in HFET´s with the total epilayer thickness less than 1.5 μm, the thermal impedance, /spl Theta/ is primarily determined by the substrate material and not by the material of the active layer. For our devices grown on 6H-SiC substrates, we measured /spl Theta/ of approximately 2/spl deg/C/spl middot/mm/W, which was more than an order of magnitude smaller than /spl Theta/=25/spl deg/C mm/W measured for similar AlGaN/GaN HFET´s grown on sapphire. Our results demonstrate that AlGaN-GaN HFET´s grown on SiC substrates combine advantages of superior electron transport properties in AlGaN/GaN heterostructures with excellent thermal properties of SiC, which should make these devices suitable for high-power electronic applications.