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 (1 over bar 010)$( {\bar 1010} )$ alpha-, (2 over bar 01)$( {\bar 201} )\;$beta-, and (001) kappa-Ga2O3 thin films on sapphire are investigated. At approximate to 80 nm, the measured TC of alpha (8.8 W m-1 K-1) is approximate to 1.8 times and approximate to 3.0 times larger than that of beta and kappa, respectively, consistent with model based on density functional theory (DFT), whereas the model reveals a similar TC for the bulk alpha- and beta-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. The study investigates the heat transport through nanoscale Ga2O3 thin films. The thermal conductivity (TC) and thermal boundary conductance (TBC) of three different phases (alpha, beta, kappa) approximate to 50-150 nm Ga2O3 thin films on sapphire are studied. Phonon-based model unveils the phase and size dependencies on the Ga2O3 TC and TBC.image