Resistive and ballistic phonon transport in $\beta$-Ga${}_2$O${}_3$

Abstract

The anisotropic thermal conductivity and the phonon mean free path (mfp) in monoclinic $\beta$-Ga${}_2$O${}_3$ single crystals and homoepitaxial films of several $\mu$m were determined using the 3$\omega$-method in the temperature range from 10K-300 K. The measured effective thermal conductivity of both, single crystal and homoepitaxial films are in the order of 20 W/(mK) at room temperature, below 30 K it increases with a maximum of 1000 to 2000 W/(mK) and decreases with T${}^3$ below 25 K. Analysis of the phonon mfp shows a dominance of phonon-phonon-Umklapp scattering above 80 K, below which the influence of point-defect scattering is observed. Below 30 K the phonon mfp increases until it is limited by the total $\beta$-Ga${}_2$O${}_3$ sample size. A crossover from resistive to ballistic phonon transport is observed below 20 K and boundary effects of the total sample size become dominant. This reveals that the homoepitaxial film-substrate interface is highly phonon-transparent. The resistive and ballistic phonon transport regimes in $\beta$-Ga${}_2$O${}_3$ are discussed corresponding to the models of Callaway and Majumdar, respectively.

16 pages, 5 figures, plus supplementary material

References in corpus (2)

• Anisotropic Thermal Conductivity in Single Crystal beta-Gallium Oxide
• Temperature-dependent thermal conductivity in Mg-doped and undoped $\beta$-$\mathrm{G}{\mathrm{a}}_2{\mathrm{O}}_3$ bulk-crystals