Three-dimensional anisotropic thermal conductivity tensor of single crystalline β-Ga2O3

β-Ga2O3 has attracted considerable interest in recent years for high power electronics, where the thermal properties of β-Ga2O3 play a critical role. The thermal conductivity of β-Ga2O3 is expected to be three-dimensionally (3D) anisotropic due to the monoclinic lattice structure. In this work, the 3D anisotropic thermal conductivity tensor of a (010)-oriented β-Ga2O3 single crystal was measured using a recently developed elliptical-beam time-domain thermoreflectance method. Thermal conductivity along any direction in the (010) plane as well as the one perpendicular to the (010) plane can be directly measured, from which the 3D directional distribution of the thermal conductivity can be derived. Our measured results suggest that at room temperature, the highest in-plane thermal conductivity is along a direction between [001] and [102], with a value of 13.3 ± 1.8 W m−1 K−1, and the lowest in-plane thermal conductivity is close to the [100] direction, with a value of 9.5 ± 1.8 W m−1 K−1. The through-plane thermal conductivity, which is along the [010] direction, has the highest value of 22.5 ± 2.5 W m−1 K−1 among all the directions. The temperature-dependent thermal conductivity of β-Ga2O3 was also measured and compared with a theoretical model calculation to understand the temperature dependence and the role of impurity scattering.