Molecular dynamics study of thermal transport across Ga2O3-diamond interfaces

β-Ga₂O₃ has an ultra-wide bandgap of 4.8 eV, a corresponding breakdown field of about 8 MVcm^-1  as well as a greatly higher Baliga figure of merit, the metric for vertical power devices, compared to SiC or GaN. As such, it is an attractive material for potential application in ultra-high voltage electronics—even in excess of 10 kV. A major concern for its implementation in devices remains the material’s low thermal conductivity, which is anisotropic and reaching only 27Wm^-1K^-1 along the [010] axis, as overheating may result in device failure. Because of this, current research explores the integration of β-Ga₂O₃ with higher thermal conductivity substrates for better device thermal management. For instance, direct attachment of β-Ga₂O₃ to diamond via van der Waals bonding has been achieved for the purpose of a photodiode p–n junction. The effects of the orientation of the β-Ga₂O₃ crystal on the thermal transport across the interface, however, have not been explored. Other attempts at integrating gallium oxide with higher thermal conductivity substrates rely on adhesion via a thin interlayer, such as SiO₂ or Al₂O₃. Such interlayers are known to be necessary when growing diamond on a gallium oxide substrate and β-Ga₂O₃–diamond superjunctions with Al₂O₃ interlayers have been considered. Furthermore, there is evidence that the stronger bonding leads to a significant reduction in thermal boundary resistance (TBR) between Ga₂O₃ and other materials.

Here, we perform simulations to study the thermal properties of β-Ga2O3 along three main crystallographic axes, investigating how thermal conductivity varies with Ga₂O₃ layer thickness for different crystal orientations. We estimate the TBR across interfaces to van der Waals bonded diamond and to ionicly bonded amorphous Al₂O₃ for the (100), (010), and (001) faces of β-Ga₂O₃. We, thus, help identify the optimal crystallographic orientations of β-Ga₂O₃ favorable for different device concepts.