Unusual thermoelectric transport anisotropy in quasi-2D, rhombohedral GeTe

Abstract

In this study, we calculate the $T$=300 K scattering and thermoelectric transport properties of rhombohedral GeTe using first-principles modeling. The room-temperature phase of GeTe has a layered structure, with cross-plane and in-plane directions oriented parallel and perpendicular to [111], respectively. Based on rigorous electron-phonon scattering, our transport calculations reveal unusual anisotropic properties; n-type GeTe has a cross-plane electrical conductivity that is roughly 3$\times$ larger than in-plane. p-type GeTe, however, displays opposite anisotropy with in-plane conducting roughly 2$\times$ more than cross-plane, as is expected in quasi-2D materials. The power factor shows the same anisotropy as the electrical conductivity, since the Seebeck coefficient is relatively isotropic. Interestingly, cross-plane n-GeTe shows the largest mobility and power factor approaching 500 cm${}^2$/V-s and 32 $\mu$W/cm-K${}^2$, respectively. The thermoelectric figure-of-merit, $zT$, is enhanced as a result of this unusual anisotropy in n-GeTe since the lattice thermal conductivity is minimized along cross-plane. This decouples the preferred transport directions of electrons and phonons, leading to a threefold increase in $zT$ along cross-plane compared to in-plane. The n-type anisotropy results from high-velocity electron states formed by Ge p-orbitals that span across the interstitial region. This surprising behavior, that would allow the preferential conduction direction to be controlled by doping, could be observed in other quasi-2D materials and exploited to achieve higher-performance thermoelectrics.

arXiv comment11 pages, 5 figures

References in corpus (22)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Advanced capabilities for materials modelling with Quantum ESPRESSO
• Phosphorene: A New 2D Material with High Carrier Mobility
• EPW: Electron-phonon coupling, transport and superconducting properties using maximally localized Wannier functions
• Enhanced Thermoelectric Efficiency via Orthogonal Electrical and Thermal Conductances in Phosphorene
• Anisotropic in-plane thermal conductivity observed in few-layer black phosphorus
• Fröhlich electron-phonon vertex from first principles
• Ab initio study of electron-phonon interaction in phosphorene
• Ab initio Electron Mobility and Polar Phonon Scattering in GaAs
• Electronic structure and thermoelectric properties of n- and p-type SnSe from first principles calculations
• Wannier interpolation of the electron-phonon matrix elements in polar semiconductors: Polar-optical coupling in GaAs
• First-principles mode-by-mode analysis for electron-phonon scattering channels and mean free path spectra in GaAs
• First-Principles Simulation of Electron Mean-Free-Path Spectra and Thermoelectric Properties in Silicon
• Mexican Hat and Rashba Bands in Few-Layer van der Waals Materials
• Two-dimensional InSe as a potential thermoelectric material
• Mobility of 2D materials from first principles in an accurate and automated framework
• Thermoelectric properties of Bi2Te3 atomic quintuple thin films
• Dominant electron-phonon scattering mechanisms in $n$-type PbTe from first principles
• Thermoelectric Band Engineering: The Role of Carrier Scattering
• On the Calculation of Lorenz Numbers for Complex Thermoelectric Materials
• Superconductivity in electron-doped arsenene
• Optical properties of cubic and rhombohedral GeTe

Cited by in corpus (6)

• Uncovering Thermal and Electrical Properties of Sb2Te3/GeTe Superlattice Films
• Analysis of simple scattering models on the thermoelectric performance of analytical electron dispersions
• Thermoelectric calculations of ring-shaped bands in two-dimensional Bi${}_2$Te${}_3$, Bi${}_2$Se${}_3$ and Sb${}_2$Te${}_3$: a comparison of simple scattering approximations
• First-principles analysis of intravalley and intervalley electron-phonon scattering in thermoelectric materials
• Nonlinear Hall effect from long-lived valley-polarizing relaxons
• Theory of Seebeck ratchet in noncentrosymmetric electron-phonon coupled system