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

TL;DR

This study measures the temperature-dependent thermal conductivity and diffusivity of Mg-doped β-Ga2O3 single crystals along different crystallographic directions, revealing anisotropic properties consistent with phonon scattering mechanisms.

Contribution

It provides the first detailed anisotropic thermal property measurements of Mg-doped β-Ga2O3 crystals using the 2ω-method across a range of temperatures.

Findings

Thermal diffusivity and conductivity are anisotropic with a ratio of about 1.4.

Temperature dependence aligns with phonon-phonon-Umklapp scattering from 300 K to 150 K.

Point defects influence scattering processes below 150 K.

Abstract

The monoclinic crystal structure of $\beta$-$\mathrm{Ga_2O_3}$ 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 $\beta$-$\mathrm{Ga_2O_3}$ single crystal. We detect a temperature independent anisotropy factor of both the thermal diffusivity and conductivity values of $D_{[010]}/D_{[001]}=\lambda_{[010]}/\lambda_{[001]}=1.4\pm 0.1$. 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.