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

We succeeded in obtaining amorphous Si–Ge thin films containing ∼6 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 ∼1 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.