Tuning the thermal resistance of SiGe phononic interfaces across ballistic and diffusive regimes

Abstract

Interfacial thermal resistance plays a pivotal role in thermal management applications, including efficient heat dissipation, energy harvesting from waste heat, and thermal barrier coatings. This study delves into the thermal resistance characteristics of a SiGe phononic material layer, positioned between two Si or Ge thermostats (Si/SiGe/Si and Ge/SiGe/Ge). We discover that the lateral period of the phononic crystal $W_p$, which is oriented perpendicular to the direction of thermal transport, can be used as an additional parameter to modulate thermal resistance. Notably, we observed distinct transport behaviors across phononic interfaces with varying $W_p$ in ballistic and diffusive transport regimes. In the ballistic limit, particularly in thinner layers, the thermal resistance diminishes with an increase in $W_p$. Conversely, in thicker phononic layers, a local maximum in thermal resistance emerges at a specific $W_p$. For smaller thicknesses, the increased overlap in phonon density-of-states between the phononic region and the thermostats at a larger $W_p$, enhances ballistic transport, thereby reducing thermal resistance. In the diffusive limit, the interplay between mode conversion within and between [0 ${\Theta }_{Ge}$] and [${\Theta }_{Ge}$ ${\Theta }_{Si}$] ranges is pivotal for the observed maximum thermal resistances and distinct temperature profiles in the Si and Ge blocks. Our findings not only highlight differing transport mechanisms at phononic interfaces in ballistic and diffusive regimes, but also demonstrate a novel approach to tuning interfacial thermal resistances using phononic materials. This has significant implications for designing materials optimized for both heat dissipation and energy conversion applications.