Prospects of low-dimensional and nanostructured silicon-based thermoelectric materials: findings from theory and simulation

Abstract

Original citation: Neophytou, Neophytos. (2015) Prospects of low-dimensional and nanostructured siliconbased thermoelectric materials : findings from theory and simulation. The European Physical Journal B, 88 (4). Permanent WRAP url:http://wrap.warwick.ac.uk/77435 Copyright and reuse:The Warwick Research Archive Portal (WRAP) makes this work by researchers of the University of Warwick available open access under the following conditions. Copyright © and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable the material made available in WRAP has been checked for eligibility before being made available.Copies of full items can be used for personal research or study, educational, or not-for profit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. Publisher's statement:"The final publication is available at Springer via http://dx.doi.org/10.1140/epjb/e2015-50673-9 " A note on versions:The version presented here may differ from the published version or, version of record, if you wish to cite this item you are advised to consult the publisher's version. Please see the 'permanent WRAP url' above for details on accessing the published version and note that access may require a subscription. AbstractSilicon based low-dimensional materials receive significant attention as new generation thermoelectric materials after they have demonstrated record low thermal conductivities. Very few works to-date, however, report significant advances with regards to the power factor. In this review we examine possibilities of power factor enhancement in: i) low-dimensional Si channels and ii) nanocrystalline Si materials. For low-D channels we use atomistic simulations and consider ultra-narrow Si nanowires and ultra-thin Si layers of feature sizes below 15nm. Room temperature is exclusively considered. We show that, in general, low-dimensionality does not offer possibilities for power factor improvement, because although the Seebeck coefficient could slightly increase, the conductivity inevitably degrades at a much larger extend. The power factor in these channels, however, can be optimized by proper choice of geometrical parameters such as the transport orientation, confinement orientation, and confinement length scale. Our simulations show that in the case where room temperature thermal conductivities as low as κl=2 W/mK are achieved, the ZT figure of merit of an optimized Si lowdimensional channel could reach values around unity. For the second case of materials, we show that by making effective use of energy filtering, and taking advantage of the inhomogeneity within the nanocrystalline geometry, the underlying potential profile and dopant distribution, large improvements in the thermoelectric power factor can be achieved. The paper is intended...

Ultra-low thermal conductivities in large-area Si-Ge nanomeshes for thermoelectric applications

“…The effect of phonon confinement within the hollow structure and the coherent effects involved resulted in a thermal conductivity reduction of 99% in comparison to bulk silicon (~140 W K −1 m −1 ). Theoretical works 56 57 that study the effects of the porosity and roughness of silicon nano-meshed films also predict that the thermal conductivity of these structures can be significantly reduced in the presence of pores with roughened surfaces. However, the drawback of these films is the high cost and time consuming of the fabrication process.…”

Advances in the optimization of silicon-based thermoelectrics: a theory perspective

“…thickness ∼ 10 nm, both DFT and tight-binding calculations predict charge transport coefficients close to those of bulk silicon. [27,10,22] Remarkably, standard band transport models cannot justify the increase of S measured in Refs. [18,19].…”

“…SiGe alloy has indeed been used for high temperature TE energy generation since the 1960s for niche applications, such as powering space probes, and a record high ZT = 1.5 was achieved at ∼ 1250 K [9]. Yet, the deployment of TE silicon at low-temperature requires further optimization, either by enhancing the power factor through band engineering, or by reducing κ p [10]. These two goals may be achieved through different strategies, by moving in a multidimensional optimization space that encompasses chemical complexity, nanostructuring and dimensionality reduction ( Figure 1).…”

Nanostructured Silicon Used for Flexible and Mobile Electricity Generation

“…Neophytou predicted the thermal conductivities may be reduced to 2 W m −1 K −1 and the ZT value could reach ca. 1 in an optimized silicon low‐dimensional channel at room temperature according to atomistic simulations . The enhanced thermoelectric properties of silicon nanowires may open promising perspectives for the integration of thermoelectric generators in microelectronics.…”