Thermal Conductance of β-Ga2O3/Metal Interfaces

The wide-bandgap semiconductor β-Ga₂O₃ is of growing interest for high power devices. Its thermal conductivity, however, is an order of magnitude lower than commonly used semiconductors such as Si, SiC, and GaN. Thermal management is thus a central issue in device design. Our objectives in this study are twofold. First, we measure the thermal conductance of the interfaces that β-Ga₂O₃ forms with the metal layers that serve as source and drain. These interfaces may be barriers to effective heat removal and prevent optimal performance. Second, we use theoretical tools to investigate the bulk properties of the α, β, and ε phases of Ga₂O₃. The thermal conductance of the Au/β-Ga₂O₃ interface is measured using frequency-domain thermoreflectance to be 45±5 and 80±8 MW/m²-K for e-beam evaporated and sputtered Au layers. To increase the thermal conductance, an adhesion layer of Ti or Cr of thickness up to 10 nm is deposited between the β-Ga₂O₃ and the Au. The relationship of thermal conductance vs. adhesion layer thickness is finely determined for Ti and Cr. Depending on the adhesion layer material and thickness, the thermal conductance can be increased by as much as 10 times. The results are interpreted by considering the phonon density of states overlap. We apply molecular dynamics simulations to predict the lattice parameters, bulk modulus, and thermal conductivity tensor of the three bulk phases of Ga₂O₃. Our predictions for the β phase match experimental results with less than 10% error. The lattice parameters of both α and ε phases of Ga₂O₃ are within 5% error from experimental results (the other properties have not been measured). Despite the same chemical composition, we predict that the ε phase thermal conductivity is an order of magnitude lower than the α and β phases.