Quantitative characterization of self-heating effects in GaN-on-diamond HEMTs with 3C-SiC interfacial layer

We systematically investigated self-heating effects of GaN HEMTs made of the same AlGaN/GaN/3C-SiC heterostructures on diamond, 4H-SiC, and Si substrates, which were fabricated by transferring the heterostructures grown on Si substrates to diamond and 4H-SiC substrates using the surface-activated bonding technologies. We measure the temperature at the drain edge of gates of HEMTs in operation, Tj, as well as their current-voltage (I-V) characteristics to develop a model for the relationship between Tj and the normalized drain current, the drain current divided by its limit for the zero-power dissipation, which represents the negative differential conductance in the current-voltage characteristics. We estimate the thermal resistance (RTH) of HEMTs on the respective substrates by analyzing their I-V characteristics using the model, i.e. without measuring their Tj. The estimated RTH values of on-diamond HEMTs were significantly lower than those of on-4H-SiC and on-Si HEMTs. We also found that the on-state drain currents of on-diamond HEMTs were larger than those of the other two types of HEMTs by compensating the effects of difference in their threshold voltages. These results demonstrated the superiority of GaN-on-diamond configuration despite variation in the device characteristics.