Temperature-dependent thermal conductivity and diffusivity of a Mg-doped insulating β-Ga2O3 single crystal along [100], [010] and [001]

The monoclinic crystal structure of beta-Ga2O3 leads to significant anisotropy of the thermal properties. The 2 omega-method is used to measure the thermal diffusivity D in [010] and [001] direction respectively and to determine the thermal conductivity values lambda of the [100], [010] and [001] direction from the same insulating Mg-doped beta-Ga2O3 single crystal. We detect a temperature independent anisotropy factor of both the thermal diffusivity and conductivity values of D-[010]/D-[001] = lambda([010])/lambda([001]) = 1.4 +/- 0.1. The temperature dependence is in accord with phonon-phonon-Umklapp-scattering processes from 300 K down to 150 K. Below 150 K point-defect-scattering lowers the estimated phonon-phonon-Umklapp-scattering values.