Temperature-dependent thermal conductivity and diffusivity of a Mg-doped insulating $β$-$\mathrm{Ga_2O_3}$ single crystal along [100], [010] and [001]

The monoclinic crystal structure of $β$-$\mathrm{Ga_2O_3}$ leads to significant anisotropy of the thermal properties. The 2$ω$-method is used to measure the thermal diffusivity $D$ in [010] and [001] direction respectively and to determine the thermal conductivity values $λ$ of the [100], [010] and [001] direction from the same insulating Mg doped $β$-$\mathrm{Ga_2O_3}$ single crystal. We detect a temperature independent anisotropy factor of both the thermal diffusivity and conductivity values of $D_{[010]}/D_{[001]}=λ_{[010]}/λ_{[001]}=1.4\pm 0.1$. 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.

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