Theory of enhancement of thermoelectric properties of materials with nanoinclusions

Based on the concept of band bending at metal/semiconductor interfaces as an energy filter for electrons, we present a theory for the enhancement of the thermoelectric properties of semiconductor materials with metallic nanoinclusions. We show that the Seebeck coefficient can be significantly increased due to a strongly energy-dependent electronic scattering time. By including phonon scattering, we find that the enhancement of ZT due to electron scattering is important for high doping, while at low doping it is primarily due to a decrease in the phonon thermal conductivity

Heat Capacity of PbS: Isotope Effects

In recent years, the availability of highly pure stable isotopes has made possible the investigation of the dependence of the physical properties of crystals, in particular semiconductors, on their isotopic composition. Following the investigation of the specific heat ($C_p$, $C_v$) of monatomic crystals such as diamond, silicon, and germanium, similar investigations have been undertaken for the tetrahedral diatomic systems ZnO and GaN (wurtzite structure), for which the effect of the mass of the cation differs from that of the anion. In this article we present measurements for a semiconductor with rock salt structure, namely lead sulfide. Because of the large difference in the atomic mass of both constituents ($M_{\rm Pb}$= 207.21 and ($M_{\rm S}$=32.06 a.m.u., for the natural isotopic abundance) the effects of varying the cation and that of the anion mass are very different for this canonical semiconductor. We compare the measured temperature dependence of $C_p \approx C_v$, and the corresponding derivatives with respect to ($M_{\rm Pb}$ and $M_{\rm S}$), with \textit{\textit{ab initio}} calculations based on the lattice dynamics obtained from the local density approximation (LDA) electronic band structure. Quantitative deviations between theory and experiment are attributed to the absence of spin-orbit interaction in the ABINIT program used for the electronic band structure calculations.Comment: 17 pages including 10 Fig

BAND STRUCTURE AND SCATTERING MECHANISMS IN LEAD CHALCOGENIDES FROM TRANSPORT PHENOMENA

Cet article porte sur la variation avec la température de la masse effective et des mécanismes de diffusion dans PbTe, PbSe et PbS. Les méthodes d'étude de la non-parabolicité basées sur la mesure du pouvoir thermoélectrique dans un fort champ magnétique et sur le coefficient de Nernst-Ettingshausen (et d'autres coefficients cinétiques) font l'objet de discussion. Les résultats obtenus par ces méthodes sont montrés et discutés. Les mesures de non-parabolicité sont utilisées pour définir la variation en température de la masse effective et des paramètres caractérisant la diffusion. La masse effective varie avec la température proportionnellement à la bande interdite. Un certain nombre de résultats sur les effets thermoélectriques et thermomagnétiques suggèrent des processus de diffusion de porteurs fortement inélastiques dans les sels de plomb. La plus grande partie de l'inélasticité s'explique par des collisions électron-électron et, pour une part moindre, par la diffusion sur les phonons optiques. La diffusion des phonons optiques affecte essentiellement la mobilité, de la même manière que la diffusion acoustique.The non-parabolicity, temperature dependence of an effective mass and scattering mechanisms in PbTe, PbSe, PbS are considered. The methods of investigation of non-parabolicity based upon measurement of thermoelectric power in strong magnetic fields and Nernst-Ettingshausen coefficient (together with other kinetic coefficients) are discussed. The results given by these methods are shown and discussed. The data of non-parabolicity are used to define the temperature dependence of an effective mass and parameters characterizing the scattering. The effective mass varies with temperature proportionally to the energy gap. A number of experimental results on thermoelectric and thermomagnetic effects point out a considerable non-elasticity of carrier scattering in lead chalcogenides. In the main the non-elasticity is explained by carrier-carrier collisions and to a less extent it is due to scattering by optical phonons. The scattering by optical phonons affects essentially the mobility in the same manner as acoustical scattering

Semiconducting lead chalcigenides

xv, 377 p. : il.; 22 cm