Thermoelectric Properties of InA Nanowires from Full-Band Atomistic Simulations.

Damiano Archetti,Neophytos Neophytou

doi:10.3390/molecules25225350

Abstract

In this work we theoretically explore the effect of dimensionality on the thermoelectric power factor of indium arsenide (InA) nanowires by coupling atomistic tight-binding calculations to the Linearized Boltzmann transport formalism. We consider nanowires with diameters from 40 nm (bulk-like) down to 3 nm close to one-dimensional (1D), which allows for the proper exploration of the power factor within a unified large-scale atomistic description across a large diameter range. We find that as the diameter of the nanowires is reduced below d < 10 nm, the Seebeck coefficient increases substantially, as a consequence of strong subband quantization. Under phonon-limited scattering conditions, a considerable improvement of ~6× in the power factor is observed around d = 10 nm. The introduction of surface roughness scattering in the calculation reduces this power factor improvement to ~2×. As the diameter is decreased to d = 3 nm, the power factor is diminished. Our results show that, although low effective mass materials such as InAs can reach low-dimensional behavior at larger diameters and demonstrate significant thermoelectric power factor improvements, surface roughness is also stronger at larger diameters, which takes most of the anticipated power factor advantages away. However, the power factor improvement that can be observed around d = 10 nm could prove to be beneficial as both the Lorenz number and the phonon thermal conductivity are reduced at that diameter. Thus, this work, by using large-scale full-band simulations that span the corresponding length scales, clarifies properly the reasons behind power factor improvements (or degradations) in low-dimensional materials. The elaborate computational method presented can serve as a platform to develop similar schemes for two-dimensional (2D) and three-dimensional (3D) material electronic structures.

Highlights

The efficiency of thermoelectric (TE) materials is quantified by the dimensionless figure of merit ZT as: σS2 ZT = (1)κe + κl where σ is the electrical conductivity, S is the Seebeck coefficient, and κ is the thermal conductivity composed of two parts: the electronic part of the thermal conductivity, κe, and the phonon/lattice part of the thermal conductivity, κl
The conductivity σ, Seebeck coefficient S, and power factor (PF) σS2 versus the carrier density for [100] nanowires of diameters from d = 40 nm down to d = 3 nm are shown in Figure 4a–c, respectively, at T = 300 K
In this work, using atomistic full-band electronic structures coupled to the Boltzmann transport method, we theoretically investigated the thermoelectric properties of indium arsenide (InA) nanowires with diameters from d = 40 nm down to d = 3 nm

Summary

Introduction

The efficiency of thermoelectric (TE) materials is quantified by the dimensionless figure of merit ZT as: σS2 ZT = (1). Κe + κl where σ is the electrical conductivity, S is the Seebeck coefficient, and κ is the thermal conductivity composed of two parts: the electronic part of the thermal conductivity, κe , and the phonon/lattice part of the thermal conductivity, κl. Over the last several years, a myriad of materials and concepts for high ZT have evolved [1], including GeTe [2], PbTe [3], half-Heuslers [4], skutterudites [5], etc. Low-dimensional materials such as nanowires (NWs) are one of these concepts, as they can achieve extremely low thermal conductivities due to strong phonon-interface scattering. ZT values up to 1 for NWs based on several materials

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Conclusion