High Dimensionless Figure of Merit <i>ZT</i> = 1.38 Achieved in p-Type Si–Ge–Au–B Thin Film

Abstract

We succeeded in obtaining amorphous SiGe thin films containing ³6 nm nanocrystals by means of a vapor deposition. The thermal conductivity was controllable using the particle size of the nanocrystals, and a very small value of thermal conductivity ³1 W/mK was obtained with an averaged particle size less than 6 nm. The electron transport properties were improved using Au-doping to form impurity levels near the valence band top, and B-doping to control the Fermi level. With the effect of this co-doping technique and nano-structuring, we estimated obtaining ZT = 1.38 at 1100 K.

Synergetic Enhancement of the Power Factor and Suppression of Lattice Thermal Conductivity via Electronic Structure Modification and Nanostructuring on a Ni- and B-Codoped p-Type Si–Ge Alloy for Thermoelectric Application

“…Recently, we succeeded in developing a p -type Si–Ge alloy structure showing high ZT s of 1.38 and 1.63 at 973 K for thin film and bulk nanostructured composites, respectively. − In particular, an n -type Si–Ge alloy showed the highest ZT value ever reported, i.e., ∼1.88 at 873 K . This improvement was attributed to the synergetic enhancement of PF and reduced thermal conductivity, which was caused by (a) creation of a sharp peak near the valence band via Au-5d element substitution ( p -type Si–Ge, ZT = 1.38 and 1.63) and conduction band via Fe-3d element substitution ( n -type Si–Ge, ZT = 1.88), (b) optimized carrier concentration by boron doping for the p -type Si–Ge and phosphorus doping for the n -type Si–Ge, and (c) phonons scattered at the nanostructured grain interfaces.…”