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 \b{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.
@article{arxiv.1412.7472,
title = {Anisotropic Thermal Conductivity in Single Crystal beta-Gallium Oxide},
author = {Zhi Guo and Amit Verma and Fangyuan Sun and Austin Hickman and Takekazu Masui and Akito Kuramata and Masataka Higashiwaki and Debdeep Jena and Tengfei Luo},
journal= {arXiv preprint arXiv:1412.7472},
year = {2015}
}