From an environmental perspective, lead-free SnTe would be preferable for solid-state waste heat recovery if its thermoelectric figure-of-merit could be brought close to that of the leadcontaining chalcogenides. In this work, we studied the thermoelectric properties of nanostructured SnTe with different dopants, and found indium-doped SnTe showed extraordinarily large Seebeck coefficients that cannot be explained properly by the conventional two-valence band model. We attributed this enhancement of Seebeck coefficients to resonant levels created by the indium impurities inside the valence band, supported by the firstprinciples simulations. This, together with the lower thermal conductivity resulting from the decreased grain size by ball milling and hot pressing, improved both the peak and average nondimensional figure-of-merit (ZT) significantly. A peak ZT of ∼1.1 was obtained in 0.25 atom % In-doped SnTe at about 873 K.

The electron-phonon interaction is well known to create major resistance to electron transport in metals and semiconductors, whereas fewer studies are directed to its effect on phonon transport, especially in semiconductors. We calculate the phonon lifetimes due to scattering with electrons (or holes), combine them with the intrinsic lifetimes due to the anharmonic phonon-phonon interaction, all from first principles, and evaluate the effect of the electron-phonon interaction on the lattice thermal conductivity of silicon. Unexpectedly, we find a significant reduction of the lattice thermal conductivity at room temperature as the carrier concentration goes above 10 19 cm −3 (the reduction reaches up to 45% in p-type silicon at around 10 21 cm −3 ), a range of great technological relevance to thermoelectric materials. The coordinates of electrons and atomic nuclei represent the most common degrees of freedom in a solid. The full quantum mechanical treatment of the excitations in a solid thus requires the solution of the Schrödinger equation involving the coordinates of all electrons and atomic nuclei, which appears intractable in most cases. A widely applied simplification, the Born-Oppenheimer approximation (BOA) [1], makes use of the fact that the electrons' mass is much smaller than that of the nuclei, and the electrons respond to the motions of the nuclei so quickly that the nuclei can be treated as static at each instant. Under the BOA, the coordinates of the nuclei enter the electronic Schrödinger equation as external parameters, and in turn the electronic ground-state energy acts as part of the interaction energy between the nuclei given a specific configuration, with which the quantized excitations of the atomic nuclei, namely phonons, can be investigated separately from the electrons [2]. It is important to note, however, that the BOA does not separate the electronic and atomic degrees of freedom completely, and a remaining coupling term can cause transitions between the eigenstates of the electron and phonon systems [3]. This electronphonon interaction (EPI) problem was first studied by Bloch [4], and later understood as the main source of resistance to electrical conduction in metals and semiconductors at higher temperatures [3,5,6], and played the key role in the microscopic theory of superconductivity [7].While the effect of the EPI on electron transport has been widely studied in great detail and has become standard content in textbooks [3,5,6], its effect on phonon transport has received much less attention. In our opinion the reason is twofold. First of all, the carrier concentration in semiconductors for conventional microelectronic and optoelectronic applications is typically below 10 19 cm −3 [8], and as we shall show later, the impact of the EPI on phonon transport in this concentration range turns out to be too small to invoke any practical interest. On the other hand, in metals with typical carrier concentrations greater than 10 22 cm −3 , the thermal conduction is dominated by electrons, an...

The monolayer of black phosphorous, or "phosphorene", has recently emerged as a new 2D semiconductor with intriguing highly anisotropic transport properties. Existing calculations of its intrinsic phonon-limited electronic transport properties so far rely on the deformation potential approximation, which is in general not directly applicable to anisotropic materials since the deformation along one specific direction can scatter electrons traveling in all directions. We perform a first-principles calculation of the electron-phonon interaction in phosphorene based on density functional perturbation theory and Wannier interpolation.Our calculation reveals that 1) the high anisotropy provides extra phase space for electronphonon scattering, and 2) optical phonons have appreciable contributions. Both effects cannot be captured by the deformation potential calculations. Our simulation predicts carrier mobilities ~170 cm 2 /Vs for both electrons and holes at 300K, and a thermoelectric figure of merit zT of up to 0.14 in p-type impurity-free phosphorene at 500K.

Thermoelectric devices utilize waste heat to generate electricity or consume electricity to transfer heat. Sun et al. describe high electrical conductivity and ultralow thermal conductivity in the nanoporous material Ni 3 (HITP) 2 , improve the record of thermoelectric figure of merit in metal-organic frameworks (MOFs), and demonstrate that MOFs are promising candidates for thermoelectrics.

We present a first-principles framework to investigate the electron scattering channels and transport properties for polar materials by combining the exact solution of linearized electronphonon (e-ph) Boltzmann transport equation in its integral-differential form associated with the e-ph coupling matrices obtained from polar Wannier interpolation scheme. No ad hoc parameter is required throughout this calculation, and GaAs, a well-studied polar material, is used as an example to demonstrate this method. In this work, the long-range and short-range contributions as well as the intravalley and intervalley transitions in the e-ph interactions (EPIs) have been quantitatively addressed. Promoted by such mode-by-mode analysis, we find that in GaAs, the piezoelectric scattering is comparable to deformation-potential scattering for electron scatterings by acoustic phonons in EPI even at room temperature and makes a significant contribution to mobility. Furthermore, we achieved good agreement with experimental data for the mobility, and identified that electrons with mean free paths between 130 and 210 nm provide the dominant contribution to the electron transport at 300 K. Such information provides a deeper understanding on the electron transport in GaAs, and the presented framework can be readily applied to other polar materials.