Impact of Hierarchical Dopant‐Induced Microstructure on Thermoelectric Properties of P‐type Si‐Ge Alloys Revealed by Comprehensive Multi‐Scale Characterization

Dopant-induced microstructure in thermoelectric materials significantly affects thermoelectric properties and offers a potential to break the interdependence between electron and phonon transport properties. However, identifying all-scale dopant-induced microstructures and correlating them with thermoelectric properties remain a huge challenge owing to a lack of detailed microstructural characterization encompassing all length scales. Here, the hierarchical boron (B)-induced microstructures in B-doped Si80Ge20 alloys with different B concentrations are investigated to determine their precise effects on thermoelectric properties. By adopting a multi-scale characterization approach, including X-ray diffraction, scanning and transmission electron microscopy, and atom probe tomography, five distinctive B-induced phases within Si80Ge20 alloys are identified. These phases exhibit different sizes, compositions, and crystal structures. Furthermore, their configuration is comprehensively determined according to B doping concentrations to elucidate their consequential impact on the unusual changes in carrier concentration, density-of-states effective mass, and lattice thermal conductivity. The study provides insights into the intricate relationship between hierarchical dopant-induced microstructures and thermoelectric properties and highlights the importance of investigating all-scale microstructures in excessively-doped systems for determining the precise structure-property relationships. Hierarchical boron (B)-induced microstructures of BxSi80Ge20 alloys with broad length scales are fully identified with their all microstructure features. The B-induced microstructures lead to unusual variations in carrier concentration, density-of-states effective mass, and lattice thermal conductivity by their changes in distribution, volume fraction, and strain field around B-induced phases. Such intricate microstructure-property relationships determine the optimal doping concentration. image