Temperature-dependent thermal conductivity in Mg-doped and undopedβ-Ga₂O₃bulk-crystals

For β-Ga₂O₃ only little information exist concerning the thermal properties, especially the thermal conductivity λ. Here, the thermal conductivity is measured by applying the electrical 3ω-method on Czochralski-grown β-Ga₂O₃ bulk crystals, which have a thickness of 200~μ m and 800~μ m. At room temperature the thermal conductivity along the [100]-direction in Mg-doped electrical insulating and undoped semiconducting β-Ga₂O₃ is confirmed as 13± 1~Wm⁻¹K⁻¹ for both crystals. The thermal conductivity increases for decreasing temperature down to 25~K to λ(25~K)=(5.3± 0.6)· 10²~Wm⁻¹K⁻¹. The phonon contribution of λ dominates over the electron contribution below room temperature. The observed function λ(T) is in accord with phonon-phonon-Umklapp scattering and the Debye-model for the specific heat at T 90~K which is about $0.1$ fold of the Debye-temperature θD. Here a detailed discussion of the phonon-phonon-Umklapp scattering for T< θD is carried out. The influence of point defect scattering is considered for T<100~K.