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

Different phases of Ga₂O₃ have been regarded as superior platforms for making new-generation high-performance electronic devices. However, understanding of thermal transport in different phases of nanoscale Ga₂O₃ 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-Ga₂O₃ 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-Ga₂O₃. 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 Ga₂O₃/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 Ga₂O₃ thin films and paves the way for improved thermal management of high-power Ga₂O₃-based devices.