Chemical Reactions Impede Thermal Transport Across Metal/β-Ga2O3 Interfaces.

The impact of chemical reactions on the thermal boundary conductance (TBC) of Au/metal contact/β-Ga2O3 layered samples as a function of contact thickness is investigated using high-throughput thermoreflectance measurements. A maximum in TBC of 530 ± 40 (260 ± 25) MW/m2 K is discovered for a Cr (Ti) contact at a thickness of 2.5 (5) nm. There is no local maximum for a Ni contact, for which the TBC saturates at 410 ± 35 MW/m2 K for thicknesses greater than 3 nm. Relative to the Au/β-Ga2O3 interface, which has a TBC of 45 ± 7 MW/m2 K, these nanoscale contacts enhance TBC by factors of 6 to 12. The TBC maximum only exists for metals capable of forming oxides that are enthalpically favorable compared to β-Ga2O3. The formation of Cr2O3, via oxygen removal from the β-Ga2O3 substrate, is confirmed by TEM analysis. The reaction-formed oxide layer reduces the potential TBC and leads to the maximum, which is followed by a plateau at a lower value, as its thickness saturates due to passivation. Many advanced materials are prone to similar chemical reactions, impacting contact engineering and thermal management for a variety of applications.