SELF-HEATING IN HIGH-POWER ALGAN-GAN HFETS

We compare self-heating effects in AlGaN-GaN heterostructure field eff ect transistors (HFET's) grown on sapphire and SiC substrates. Heat di ssipation strongly affects the device characteristics soon after the a pplication of the source-drain voltage (in less than 10(-7) s). Our re sults 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 o ur devices grown on 6H-SiC substrates, we measured Theta of approximat ely 2 degrees C.mm/W, which was more than an order of magnitude smalle r 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 grow n on SiC substrates combine advantages of superior electron transport properties in AlGaN/GaN heterostructures with excellent thermal proper ties of SiC, which should make these devices suitable for high-power e lectronic applications.