Enhancing thermal dissipation ability and electrical performance in GaN-on-GaN HEMTs through stepped-carbon buffer design

This study investigates the thermal dissipation ability and electrical performance of GaN-on-GaN HEMTs through a stepped-C buffer design. We analyzed the relationship between impurity (C and Fe) concentrations and the thermal conductivity of the GaN material by fitting Debye–Callaway model. A stepped-C buffer design is proposed to avoid the Fe impurity and its tailing effect on thermal conduction in GaN epitaxial layers. In addition, the high concentration of C doping is designed to suppress the epitaxial interface leakage in GaN-on-GaN structures. The transducer-less transient thermoreflectance (TL-TTR) technique revealed that the stepped-C structure significantly improves thermal conductivity of epitaxial layers compared with that of Fe/C co-doped structure. Due to the optimization of heat dissipation ability, the peak temperature of the stepped-C sample decreased by ∼30 °C compared to the Fe/C co-doped sample at PDC = 10.4 W/mm. Consequently, the GaN-on-GaN HEMTs with the stepped-C buffer achieved a record output power density (Pout) of 14.8 W/mm and a power-added efficiency (PAE) of 48.2% at 3.6 GHz, underscoring the critical role of thermal management in advancing GaN-on-GaN HEMT RF performance.