Effects of nanoscale porosity on thermoelectric properties of SiGe

Abstract

The recent achievement of the high thermoelectric figure of merit in nanograined materials is attributed to the successful optimization of the consolidation process. Despite a thermal conductivity reduction, it has been experimentally observed that the porous nanograined materials have lower thermoelectric figure of merit than their bulk counterpart due to significant reduction in the electrical conductivity. In this paper, nanoscale porosity effects on electron and phonon transport are modeled to predict and explain thermoelectric properties in porous nanograined materials. Electron scattering at the pores is treated quantum mechanically while phonon transport is treated using a classical picture. The modeling results show that the charge carriers are scattered more severely in nanograined materials than the macroscale porous materials, due to a higher number density of scattering sites. Porous nanograined materials have enhanced Seebeck coefficient due to energy filtering effect and low thermal conductivity, which are favorable for thermoelectric applications. However, the benefit is not large enough to overcome the deficit in the electrical conductivity, so that a high sample density is necessary for nanograined SiGe.

Pore-size dependence of the thermal conductivity of porous silicon: A phonon hydrodynamic approach

“…2,11 A detailed knowledge of this dependence may have valuable practical consequences. Since increasing porosity also deteriorates the electron transport properties, 20,21 being able to reduce thermal conductivity by several alternative procedures opens a wider range of possibilities, which may be of interest in thermoelectric applications.…”

Effect of annealing temperature on the structural and electrical properties of mesoporous La_0.7Sr_0.3MnO₃

“…25) In general, when inducing a pore structure in conducting oxides, the electrical conductivity decreased due to increased scattering of carriers. 26) In this study, when increasing the annealing temperature, the surface area was increased but the porosity was decreased by a collapse of interior pores. For this reason, we can expect an increase in the surface area, but with slightly changed electrical conductivity.…”

Role of Nanoscale Precipitates for Enhancement of Thermoelectric Properties of Heavily P-Doped Si-Ge Alloys

“…where η, m*, k B , h, F(η), and λ are the reduced Fermi level (= E F /k B T, where E F is the Fermi level), carrier effective mass (= 1.08m 0 , 24) where m 0 is the free electron mass), Boltzmann constant, Planck constant, Fermi integral, and scattering parameter, respectively. λ is a parameter associated with the energy dependence of the charge-carrier mean free path, where we obtained λ = 0.65 by tting the literature data for bulk Si and Si-Ge alloys.…”