Temperature dependent thermal conductivity in Mg doped and undoped beta Ga2O3 bulk crystals

For $\beta$-$\mathrm{Ga_2O_3}$ only little information exist concerning the thermal properties, especially the thermal conductivity $\lambda$. Here, the thermal conductivity is measured by applying the electrical 3$\omega$-method on Czochralski-grown $\beta$-$\mathrm{Ga_2O_3}$ bulk crystals, which have a thickness of $200~\mathrm{\mu m}$ and $800~\mathrm{\mu m}$. At room temperature the thermal conductivity along the [100]-direction in Mg-doped electrical insulating and undoped semiconducting $\beta$-$\mathrm{Ga_2O_3}$ is confirmed as $13\pm 1~\mathrm{Wm^{-1}K^{-1}}$ for both crystals. The thermal conductivity increases for decreasing temperature down to $25~\mathrm{K}$ to $\lambda(25~\mathrm{K})=(5.3\pm 0.6)\cdot 10^2~\mathrm{Wm^{-1}K^{-1}}$. The phonon contribution of $\lambda$ dominates over the electron contribution below room temperature. The observed function $\lambda(T)$ is in accord with phonon-phonon-Umklapp scattering and the Debye-model for the specific heat at $T\gtrsim 90~\mathrm{K}$ which is about $0.1$ fold of the Debye-temperature $\theta_\mathrm{D}$. Here a detailed discussion of the phonon-phonon-Umklapp scattering for $T< \theta_\mathrm{D}$ is carried out. The influence of point defect scattering is considered for $T<100~\mathrm{K}$.Comment: 11 pages, 6 figure

Analysis of the scattering mechanisms controlling electron mobility in β

Electron density and Hall mobility data were simultaneously analyzed in the frame of the relaxation time approximation in order to identify the main scattering mechanisms that limit the carrier mobility in β-Ga2O3 single crystals. The Hall factor correction was self-consistently included in the fitting procedure. The analysis indicates that low-energy optical phonons provide the main scattering mechanism, via lattice deformation. In this regard, a deformation potential of about 4×109 eV cm−1 was estimated. Furthermore, it is shown that the Hall coefficient and mobility can be measured by the usual experimental geometry, and the standard transport theory can be applied when off-diagonal elements of the resistivity tensor at zero magnetic field are negligible with respect to the diagonal ones. This directly follows from the analysis of the magneto-resistive tensor of a semiconductor with monoclinic structure. Such a requirement is satisfied under the hypothesis of nearly spherical energy surfaces, as has been reported to occur at the Γ minimum of the conduction band of β-Ga2O3