Reduced thermal boundary conductance in GaN-based electronic devices introduced by metal bonding layer

Achieving high interface thermal conductance is one of the biggest challenges in the nanoscale heat transport of GaN-based devices such as light emitting diodes (LEDs), and high electron mobility transistors (HEMTs). In this work, we experimentally measured thermal boundary conductance (TBC) at interfaces between GaN and the substrates with AuSn alloy as a commonly-used adhesive layer by time-domain thermoreflectance (TDTR). We find that the TBCs of GaN/Ti/AuSn/Ti/Si, GaN/Ti/AuSn/Ti/SiC, and GaN/Ti/AuSn/Ti/diamond, are 16.5, 14.8, and 13.2 MW·m⁻²·K⁻¹ at room temperature, respectively. Our measured results show that the TBC of GaN/Ti/AuSn/Ti/SiC interface is inferior to the TBC of pristine GaN/SiC interface, due to the large mismatch of phonon modes between AuSn/Ti and substrates, shown as the difference of Debye temperature of two materials. Overall, we measured the TBC at interface between GaN and thermal conductive substrates, and provided a guideline for designing the interface between GaN and substrate at HEMT from a thermal management point of view.