Thermoelectric properties of InAs nanowires from full-band atomistic simulations

TL;DR

This study uses atomistic simulations to analyze how reducing nanowire diameter affects thermoelectric properties, revealing a significant power factor increase around 10 nm diameter, influenced by quantum effects and surface roughness.

Contribution

It provides a comprehensive atomistic simulation framework to understand thermoelectric behavior in InAs nanowires across a wide size range, including effects of surface roughness.

Findings

Power factor increases ~6x at 10 nm diameter without surface roughness.

Surface roughness reduces power factor improvement to ~2x.

Power factor diminishes at diameters below 3 nm.

Abstract

In this work we theoretically explore the effect of dimensionality on the thermoelectric power factor of InAs nanowires by coupling atomistic tight-binding calculations to the Linearized Boltzmann transport formalism. We consider nanowires with diameters from 40nm (bulk-like) down to 3nm (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, a consequence of strong subband quantization. Under phonon-limited scattering conditions, a considerable improvement of ~6x 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 ~2x. As the diameter is decreased down 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 2D and 3D material electronic structures.