Microstructure and thermoelectric properties of Ga-DOPED SiGe alloys prepared by mechanical alloying and induction hot pressing

Abstract

Ga -doped SiGe alloys were prepared by high energy ball milling followed by induction hot pressing. The grain size decreases dramatically with increasing mill time, and nanostructured features in the range 3–500 nm were introduced after extensive ball milling for 2–12 h. The bulk alloys hot pressed from 2 h and 6 h dry-milled powders consist of different compositions of micron- to nanosized Si y Ge 100-y, where Ga prefers to locate in the submicron- and nanosized Ge -rich phase and form a modulation-doping structure. The samples hot pressed from 12 h wet-milled powders are more homogeneous in microstructure and composition. Property characterization shows that although Ga -doping leads to p-type conduction, only part of Ga atoms is incorporated as dopant in the SiGe solid solution phase. Samples hot pressed from 2 h and 6 h dry-milled powders have higher power factors, while those hot pressed from 12 h wet-milled powders posses much lower thermal conductivity. The maximum figure of merit (ZT) is 0.51 at 805°C for the 6 h dry-milled and hot pressed sample with the nominal composition Si 80 Ge 18 Ga 2.