Superdiffusive Thermal Transport in Si_0.4Ge_0.6 Thin Films

Superdiffusive thermal transport represents a unique phenomenon in heat conduction, which is characterized by a size (<i>L</i>) dependence of thermal conductivity (<i>κ</i>) in the form of <i>κ</i> ~ <i>L</i>^β with a constant β between 0 and 1. Although superdiffusive thermal transport has been theoretically predicted for SiGe alloys, direct experimental evidence is still lacking. Recently, we conducted a systematic experimental study of the thickness-dependent thermal conductivity of Si_0.4Ge_0.6 thin films grown by molecular beam epitaxy (MBE). The cross-plane thermal conductivity of Si_0.4Ge_0.6 thin films spanning a thickness range from 20 to 1120 nm was measured in the temperature range of 120-320 K <i>via</i> a differential three-omega method. Results show that the thermal conductivity follows a consistent <i>κ</i> ~ <i>t</i>^0.26 power law with the film thickness (<i>t</i>) at different temperatures, providing direct experimental evidence that alloy-scattering dominated thermal transport in SiGe is superdiffusive.