Thermal conductivity of rutile germanium dioxide
Sieun Chae, Kelsey Mengle, Ruiming Lu, Alan Olvera, Nocona Sanders, Jungho Lee, Pierre F. P. Poudeu, John T. Heron, Emmanouil Kioupakis
Abstract
Power electronics seek to improve power conversion of devices by utilizing materials with a wide bandgap, high carrier mobility, and high thermal conductivity. Due to its wide bandgap of 4.5 eV, β-Ga2O3 has received much attention for high-voltage electronic device research. However, it suffers from inefficient thermal conduction that originates from its low-symmetry crystal structure. Rutile germanium oxide (r-GeO2) has been identified as an alternative ultra-wide-bandgap (4.68 eV) semiconductor with a predicted high electron mobility and ambipolar dopability; however, its thermal conductivity is unknown. Here, we characterize the thermal conductivity of r-GeO2 as a function of temperature by first-principles calculations, experimental synthesis, and thermal characterization. The calculations predict an anisotropic phonon-limited thermal conductivity for r-GeO2 of 37 W m−1 K−1 along the a direction and 58 W m−1 K−1 along the c direction at 300 K where the phonon-limited thermal conductivity predominantly occurs via the acoustic modes. Experimentally, we measured a value of 51 W m−1 K−1 at 300 K for hot-pressed, polycrystalline r-GeO2 pellets. The measured value is close to our directionally averaged theoretical value, and the temperature dependence of ∼1/T is also consistent with our theory prediction, indicating that thermal transport in our r-GeO2 samples at room temperature and above is governed by phonon scattering. Our results reveal that high-symmetry UWBG materials, such as r-GeO2, may be the key to efficient power electronics.