Novel metal/semiconductor nanocomposite and superlattice materials and devices for thermoelectrics

Efficiency of thermoelectric materials is generally discussed in terms of the dimensionless figure-of-merit, ZT = S 2 σT/κ, Many researchers have found that it is possible to reduce the lattice thermal conductivity by incorporating nanostructures (i.e. nanoparticles or heterobarriers) into materials, thereby scattering phonons. At the same time, it has been theoretically predicted and experimentally demonstrated that barriers can be used to "filter" the distribution of carriers which contribute to conduction. By doing so, it is possible to significantly increase the Seebeck coefficient while only modestly decreasing the electrical conductivity. As a result of this energy-dependent scattering of carriers, the thermoelectric power factor is increased. We present theoretical and experimental results for metal/semiconductor nanocomposites consisting of metallic rareearth- group V nanoparticles within III-V semiconductors (e.g. ErAs:InGaAlAs) demonstrating both an increase in thermoelectric power factor and a decrease in thermal conductivity, resulting in a large figure of merit. We also discuss metal/semiconductor superlattices made of lattice-matched nitride materials for electron filtering and the prospects of these materials for efficient thermoelectrics, especially at high temperatures. Finally, we will discuss both various synthesis techniques for these materials, including the prospects for bulk growth, and also devices fabricated from these materials.