Ultralow thermal conductivity of amorphous silicon-germanium thin films for alloy and disorder scattering determined by 3ω method and nanoindentation

The ultralow thermal conductivity (1.3 W/(m center dot K)) of amorphous silicon-germanium films for alloy and disorder scattering was investigated using the 3 omega method and nanoindentation. The films exhibited the lowest phonon mean free path (MFP) of 0.5 nm compared to that of amorphous silicon (1.1 nm) and germanium (0.9 nm) films, owing to alloy scattering in the silicon-germanium films. Based on Matthiessen's rule, the phonon MFPs of the amorphous silicon-germanium films contributing to alloy and disorder scattering were calculated to be 1.0 nm for both. Therefore, alloy and disorder scattering contribute equally to the reduction in the phonon MFP.