Electronic structure and thermoelectric properties ofn- andp-type SnSe from first-principles calculations

Abstract

We present results of the electronic band structure, Fermi surface and electron transport properties calculations in the orthorhombic n-and p-type SnSe, applying the Korringa-Kohn-Rostoker method and the Boltzmann transport approach. The analysis accounted for the temperature effect on crystallographic parameters in P nma structure as well as the phase transition to CmCm structure at Tc ∼ 807 K. Remarkable modifications of the conduction and valence bands were notified upon varying crystallographic parameters within the structure before Tc, while the phase transition mostly leads to the jump in the band gap value. The diagonal components of the kinetic parameter tensors (velocity, effective mass) and resulting transport quantity tensors (electrical conductivity σ, thermopower S and power factor PF) were computed in a wide range of temperature (15 − 900 K), and hole (p−type) and electron (n−type) concentrations (10 17 − 10 21 cm −3 ). SnSe is shown to have a strong anisotropy of the electron transport properties for both types of charge conductivity, as expected for the layered structure, with the generally heavier p-type effective masses, comparing to n-type ones. Interestingly, p-type SnSe has strongly non-parabolic dispersion relations, with the 'pudding-mold'-like shape of the highest valence band. The analysis of σ, S and PF tensors indicates, that the inter-layer electron transport is beneficial for thermoelectric performance in ntype SnSe, while this direction is blocked in p-type SnSe, where in-plane transport is preferred. Our results predict, that the n-type SnSe is potentially even better thermoelectric material than the ptype one. Theoretical results are compared with the single crystal p-SnSe measurements, and a good agreement is found below 600 K. The discrepancy between the computational and experimental data, appearing at higher temperatures, can be explained assuming an increase of the hole concentration vs. T , which is correlated with the experimental Hall data. arXiv:1502.04599v3 [cond-mat.mtrl-sci]

First-Principles Calculations of Thermoelectric Properties of IV–VI Chalcogenides 2D Materials

“…The lattice thermal conductivity values obtained in the present work are in good agreement with recently reported results (Qin et al, 2016;Shafique and Shin, 2017). If we consider the lattice thermal conductivity as a good approach to obtain high efficiency (ZT) in TE materials, we can expect, from our results (Figure 6), that the monolayer SnSe should be one of the best candidate for TE applications as we can see in previously reports for this material (Carrete et al, 2014;Zhao et al, 2014Zhao et al, , 2016Guan et al, 2015;Guo et al, 2015;Hong et al, 2015;Kutorasinski et al, 2015;Sassi et al, 2015;Wang et al, 2015;Chere et al, 2016;Leng et al, 2016;Morales Ferreiro et al, 2016;Popuri et al, 2016;Li et al, 2017).…”

First-principles calculations of thermal, electrical, and thermoelectric transport properties of semiconductors

“…These parametrized models for the electron scattering process have helped to understand the electron transport properties in certain thermoelectric materials and give qualitative agreement with the experiment [113][114][115][116][117]. However, such methods lack the accuracy if the band structure becomes complicated, in which case the electron phonon coupling no longer satisfies a simple parametrized model.…”

Direct observation of double valence-band extrema and anisotropic effective masses of the thermoelectric material SnSe

“…by approximately 20 meV. The calculated energy difference between the maxima of the two bands may increase as a function of temperature, 9) and values of less than 1 meV (calculated from the measured lattice constants at 300 K) 8) and 60 meV (calculated from the measured lattice constants at 600 K and structure-relaxed) 7) have been reported (Table I) We can deduce the effective mass along the c and parallel to the b directions on the measured momentum plane using a parabolic fit to the band positions, as shown in Figs. Table I.…”