Self-heating in high-power AlGaN-GaN HFET's

We compare self-heating effects in AlGaN-GaN heterostructure field effect transistors (HFET's) 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(-7) s). Our results show that in HFET's with the total epilayer thickness less than 1.5 mu m, the thermal impedance, 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 Theta of approximately 2 degrees C.mm/W, which was more than an order of magnitude smaller than Theta = 25 degrees 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.