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A theoretical model has been developed (Klemens 1987) that predicts that the addition of ultra-fine, inert, phonon-scattering centers to SiGe thermoelectric material will reduce its thermal conductivity and improve its figure-of-merit. To investigate this prediction, ultra-fine particulates (20Å to 200Å) of boron nitride have been added to boron doped, p-type, 80/20 SiGe. All previous SiGe samples produced from ultra-fine SiGe powder without additions had lower thermal conductivities than standard SiGe, but high temperature (1525K) heat treatment increased their thermal conductivity back to the value for standard SiGe. However, the SiGe samples with inert boron nitride or silicon nitride, phonon-scattering centers retained the lower thermal conductivity after multiple heat treatments at 1525K.

The effect of changes in the carrier concentration and mobility for heavily doped n-type SiGe on the electrical power factor has been investigated. It has been shown that power factors of 37-40 μV/cm-K2 can be achieved with carrier concentrations of 2.0 - 2.5 × 1020 cm-3 and mobilities of 38-40 cm2/V-sec. Many samples with suitable carrier concentration do not have high mobilities and some rationale for this behavior is presented. Initial results are presented on fabrication of n-type samples from ultra-fine powders. The emphasis in this work is to achieve thermal conductivity reductions by adding inert particles to scatter mid-frequency phonons.