Thermal Conductivity Reduction and Thermoelectric Figure of Merit Increase by Embedding Nanoparticles in Crystalline Semiconductors

Atomic substitution in alloys can efficiently scatter phonons, thereby reducing the thermal conductivity in crystalline solids to the “alloy limit.” Using ${\mathrm{In}}_{0.53}{\mathrm{Ga}}_{0.47}\mathrm{As}$ containing ErAs nanoparticles, we demonstrate thermal conductivity reduction by almost a factor of 2 below the alloy limit and a corresponding increase in the thermoelectric figure of merit by a factor of 2. A theoretical model suggests that while point defects in alloys efficiently scatter short-wavelength phonons, the ErAs nanoparticles provide an additional scattering mechanism for the mid-to-long-wavelength phonons.

Figure 1

(a) The effect of ML thickness on the thermal conductivity of a $\mathrm{ErAs}/{\mathrm{In}}_{0.53}{\mathrm{Ga}}_{0.47}\mathrm{As}$ superlattice. The thermal conductivity of ${\mathrm{In}}_{0.53}{\mathrm{Ga}}_{0.47}\mathrm{As}$ (open circles) is shown as a comparison. ErAs deposition is varied from 0.05 ML (open downward triangles), 0.1 ML (solid upward triangles), 0.2 ML (open diamonds), to 0.4 ML (open squares). The inset shows TEM pictures of 0.4 ML with a 40 nm period thickness $\mathrm{ErAs}/{\mathrm{In}}_{0.53}{\mathrm{Ga}}_{0.47}\mathrm{As}$ superlattice. (b) The effect of superlattice period on the thermal conductivity of a $\mathrm{ErAs}/{\mathrm{In}}_{0.53}{\mathrm{Ga}}_{0.47}\mathrm{As}$ superlattice. Two different depositions are considered. One is 0.1 ML with 40 nm (solid upward triangles) and 10 nm (open upward triangles) and the other is 0.05 ML with 40 nm (open downward triangles) and 5 nm (solid downward triangles).

Figure 2

(a) Thermal conductivity of randomly distributed ErAs in ${\mathrm{In}}_{0.53}{\mathrm{Ga}}_{0.47}\mathrm{As}$ (solid circles). Thermal conductivity of a ${\mathrm{In}}_{0.53}{\mathrm{Ga}}_{0.47}\mathrm{As}$ alloy (open circles), 0.4 ML with a 40 nm period thickness $\mathrm{ErAs}/{\mathrm{In}}_{0.53}{\mathrm{Ga}}_{0.47}\mathrm{As}$ superlattice (open squares) and 0.1 ML with a 10 nm period thickness $\mathrm{ErAs}/{\mathrm{In}}_{0.53}{\mathrm{Ga}}_{0.47}\mathrm{As}$ superlattice (open upward triangles) are shown as references. Dotted and solid lines are based on theoretical analysis. The inset shows TEM pictures of randomly distributed ErAs in ${\mathrm{In}}_{0.53}{\mathrm{Ga}}_{0.47}\mathrm{As}$. Another inset shows the phonon mean free path (MFP) versus normalized frequency at 300 K. (b) Resulting enhancement of the thermoelectric figure of merit at 300 K. Thermal conductivity, power factor, and the figure of merit $ZT$ of randomly distributed ErAs in ${\mathrm{In}}_{0.53}{\mathrm{Ga}}_{0.47}\mathrm{As}$ are normalized by the corresponding values of ${\mathrm{In}}_{0.53}{\mathrm{Ga}}_{0.47}\mathrm{As}$.