Defect engineering of thermal conductivity in Si and Ge

Defect engineering offers a powerful route for tuning lattice thermal conductivity, yet a systematic comparison of the relative impact of distinct point defects and their extended counterparts has remained underexplored. Using equilibrium molecular dynamics simulations, we quantify how vacancy, interstitial, substitutional, and void (extended) defects affect lattice thermal conductivity in crystalline Si and Ge.

Across all concentrations studied, vacancy and interstitial defects produce the greatest suppression of thermal conductivity, while substitutional and void defects scatter phonons more weakly — and the gap between defect classes narrows as defect concentration drops. To explain these trends, we examine the mass-weighted phonon density of states, showing that defects introducing large local strain fields or strong mass perturbations drive the largest changes in the vibrational spectrum.

Together, these results give a unified, comparative picture of how different defect classes in Si and Ge scatter phonons and limit thermal transport, supporting more rational defect-level design for thermal management applications. See (Tang et al., 2026) for the full study.