Thermal Resistance Extraction of AlGaN/GaN Depletion-Mode HEMTs on Diamond

Thermal resistances of AlGaN/GaN high electron mobility transistors (HEMTs) on polycrystalline diamond (with thermal conductivity >1500 W/m K) and on Si substrates are respectively extracted and compared. GaN HEMTs on diamond and on Si with the same device dimensions were fabricated and their direct-current (DC) characteristics were compared. Thermally-induced negative differential output resistance in the saturation region at DC was observed for GaN-on-Si HEMT but was negligible for the GaN-on-diamond device at comparable power densities, which is consistent with reduced thermal resistance. Thermal resistances of the HEMTs on Si and diamond substrates determined experimentally from analysis of I–V characteristics agree with estimates based on simulation.