Different phases of Ga2 O3 have been regarded as superior platforms for making new-generation high-performance electronic devices. However, understanding of thermal transport in different phases of nanoscale Ga2 O3 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-Ga2 O3 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-Ga2 O3 . 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 Ga2 O3 /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 Ga2 O3 thin films and paves the way for improved thermal management of high-power Ga2 O3 -based devices.
Keywords: Ga2O3; first-principles; polymorphs; thermal boundary conductance; thermal conductivity; transient thermoreflectance.
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