Nanoscale thermal transport in amorphous and crystalline GeTe thin-films

Abstract

We use frequency-domain thermoreflectance to determine the predominant phonon scattering mechanisms in thin films of GeTe. Thickness-dependent thermal conductivity is measured at room temperature to determine an effective mean free path for heat energy carriers in both amorphous and polycrystalline GeTe thin films and to subsequently compare intrinsic defect scattering with the magnitude of boundary scattering that occurs due to nanostructuring. Similarities in the effective mean free paths of amorphous and polycrystalline GeTe suggest that the crystalline alloy's microstructure results in a magnitude of intrinsic scattering between phonons comparable to that experienced by the amorphous phase. Variability in thermal conductivity between phases at comparable thicknesses is attributed to differences in volumetric heat capacity and phonon group velocity. These results are critical for the design of next-generation nanophotonic and optoelectronic devices that utilize nanostructured chalcogenide glasses.