Anisotropic Thermal Conductivity in Single Crystal beta-Gallium Oxide

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The thermal conductivities of beta-Ga2O3 single crystals along four different crystal directions were measured in the temperature range of 80-495K using the time domain thermoreflectance (TDTR) method. A large anisotropy was found. At room temperature, the [010] direction has the highest thermal conductivity of 27.0+/-2.0 W/mK, while that along the [100] direction has the lowest value of 10.9+/-1.0 W/mK. At high temperatures, the thermal conductivity follows a 1/T relationship characteristic of Umklapp phonon scattering, indicating phonon-dominated heat transport in the eta-Ga2O3 crystal. The measured experimental thermal conductivity is supported by first-principles calculations which suggest that the anisotropy in thermal conductivity is due to the differences of the speed of sound along different crystal directions.