Role of Nanoscale Precipitates for Enhancement of Thermoelectric Properties of Heavily P-Doped Si-Ge Alloys

Abstract

Thermoelectric (TE) devices can save energy by generating electricity from waste heat. For industrial application of TE power generation, TE materials with high conversion efficiency and that are non-toxic and inexpensive are required. The nanostructured silicon-germanium (Si-Ge) alloy is one possible candidate for such TE materials. Nanostructuring is an effective way to improve the conversion efficiency of materials because it dramatically reduces the lattice thermal conductivity (κlat). Here, we experimentally demonstrate effective phonon blocking without carrier mobility deterioration in bulk Si-Ge alloys containing phosphorous-rich nanoscale precipitates connected coherently or semi-coherently with the matrix phase. When the Ge content was less than 5%, the nanoscale precipitates effectively scattered heat-carrying phonons, leading to a sufficient reduction in κlat. However, at higher Ge content compositions, phonon scattering by Ge substitution with Si was more predominant than phonon scattering by nanoscale precipitates for the reduction of κlat. As a result, significant enhancement of zT was achieved at low Ge contents.