Three-Dimensional Anisotropic Thermal Conductivity Tensor of Single Crystalline \b{eta}-Ga2O3

TL;DR

This study measures the three-dimensional anisotropic thermal conductivity tensor of single crystalline ta-Ga2O3 using a novel TDTR method, revealing directional thermal conductivities and their temperature dependence relevant for high power electronics.

Contribution

The paper introduces a novel TDTR technique with an elliptical beam to measure the 3D anisotropic thermal conductivity tensor of ta-Ga2O3 single crystals, providing detailed directional data.

Findings

Highest in-plane thermal conductivity is between [001] and [102] directions.

Lowest in-plane thermal conductivity is near the [100] direction.

Through-plane thermal conductivity along [010] is the highest at room temperature.

Abstract

\b{eta}-Ga2O3 has attracted considerable interest in recent years for high power electronics, where thermal properties of \b{eta}-Ga2O3 play a critical role. The thermal conductivity of \b{eta}-Ga2O3 is expected to be three-dimensionally (3D) anisotropic due to the monoclinic lattice structure. In this work, the 3D anisotropic thermal conductivity tensor of a (010)-oriented \b{eta}-Ga2O3 single crystal was measured by using a novel time-domain thermoreflectance (TDTR) method with a highly elliptical pump beam. Our measured results suggest that at room temperature, the highest in-plane thermal conductivity is along a direction between [001] and [102], with a value of 13.3+/-1.8 W/mK, and the lowest in-plane thermal conductivity is close to the [100] direction, with a value of 9.5+/-1.8 W/mK. The through-plane thermal conductivity, which is along the [010] direction, has the highest value of 22+/-2.5 W/mK among all the directions. Temperature-dependent thermal conductivity of \b{eta}-Ga2O3 was also measured and compared with a modified Callaway model calculation to understand the temperature dependence and the role of impurity scattering.