Phase‐Dependent Phonon Heat Transport in Nanoscale Gallium Oxide Thin Films

Abstract Different phases of Ga 2 O 3 have been regarded as superior platforms for making new‐generation high‐performance electronic devices. However, understanding of thermal transport in different phases of nanoscale Ga 2 O 3 thin‐films remains challenging, owing to the lack of phonon transport models and systematic experimental investigations. Here, thermal conductivity (TC) and thermal boundary conductance (TBC) of the α ‐, β ‐, and (001) κ ‐Ga 2 O 3 thin films on sapphire are investigated. At ≈80 nm, the measured TC of α (8.8 W m −1 K −1 ) is ≈1.8 times and ≈3.0 times larger than that of β and κ , respectively, consistent with model based on density functional theory (DFT), whereas the model reveals a similar TC for the bulk α‐ and β ‐Ga 2 O 3 . The observed phase‐ and size‐dependence of TC is discussed thoroughly with phonon transport properties such as phonon mean free path and group velocity. The measured TBC at Ga 2 O 3 /sapphire interface is analyzed with diffuse mismatch model using DFT‐derived full phonon dispersion relation. Phonon spectral distribution of density of states, transmission coefficients, and group velocity are studied to understand the phase‐dependence of TBC. This study provides insight into the fundamental phonon transport mechanism in Ga 2 O 3 thin films and paves the way for improved thermal management of high‐power Ga 2 O 3 ‐based devices.