Gated Si nanowires for large thermoelectric power factors

Neophytou, Neophytos; Kosina, H.

doi:10.1063/1.4893977

Cited by 14 publications

(22 citation statements)

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“…This is attributed to the adverse interdependence of the electrical conductivity and Seebeck coefficient via the carrier density, which proves very difficult to overcome. To achieve power factor improvements, current efforts revolve around engineering the density of states of lowdimensional materials, 2-6 modulation doping, [7][8][9][10] introducing energy resonances in the density of states, 11,12 and energy filtering in nanocomposites and superlattices. [13][14][15][16][17][18][19][20][21][22] Although theoretical works indicate that power factor improvements are possible, to-date experiments do not commonly demonstrate significant success in realizing these improvements.…”

Section: Introductionmentioning

confidence: 99%

The influence of non-idealities on the thermoelectric power factor of nanostructured superlattices

Thesberg

Pourfath

Kosina

et al. 2015

Journal of Applied Physics

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Cross-plane superlattices composed of nanoscale layers of alternating potential wells and barriers have attracted great attention for their potential to provide thermoelectric power factor improvements and higher ZT figure of merit. Previous theoretical works have shown that the presence of optimized potential barriers could provide improvements to the Seebeck coefficient through carrier energy filtering, which improves the power factor by up to 40%. However, experimental corroboration of this prediction has been extremely scant. In this work, we employ quantum mechanical electronic transport simulations to outline the detrimental effects of random variation, imperfections, and non-optimal barrier shapes in a superlattice geometry on these predicted power factor improvements. Thus, we aim to assess either the robustness or the fragility of these theoretical gains in the face of the types of variation one would find in real material systems. We show that these power factor improvements are relatively robust against: overly thick barriers, diffusion of barriers into the body of the wells, and random fluctuations in barrier spacing and width. However, notably, we discover that extremely thin barriers and random fluctuation in barrier heights by as little as 10% is sufficient to entirely destroy any power factor benefits of the optimized geometry. Our results could provide performance optimization routes for nanostructured thermoelectrics and elucidate the reasons why significant power factor improvements are not commonly realized in superlattices, despite theoretical predictions. V C 2015 AIP Publishing LLC.

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Section: Introductionmentioning

confidence: 99%

The influence of non-idealities on the thermoelectric power factor of nanostructured superlattices

Thesberg

Pourfath

Kosina

et al. 2015

Journal of Applied Physics

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“…Here Vsd is the bias voltage. There is some recent observation [22][23][24][25][26][27][28][29][30][31][32] which also reveals the same behaviour. T=0K T=3K T=5K T=0K T=3K T=5K T=0K T=3K 0 …”

Section: Discussion Of Resultsmentioning

confidence: 59%

A theoretical study of electron transport through a quantum wire (QW) with a side quantum dots (QD’s) array and quantum point contacts (QPCs) and evaluation of conductance as a function of Fermi energy

2017

JCBSC

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Abstract:Using the theoretical formalism of P. A. Orellana etal (Phys. Rev B67, 085321 (2003)), we have theoretically evaluated the conductance in the unit of (2e 2 /h) as a function of Fermi energy in the unit of  for N=1 to N=10 QD"s array. Our theoretically evaluated results indicate that as N increases the system develops an oscillating band. One observes N anti-resonances and N-1 resonance which arises due to hybridization of the quasi bound levels of QD's and the coupling of the QW. This study also reveals an important fact that electron-electron interaction in this system is more effective. The main effect of this interaction is to shift and split the resonance position. Using the theoretical formalism of P. Havu etal [Phys. Rev. B70, 233308(2004)], we have also studied electron transport through QW and quantum point contacts. We observed that conductance of different length of QW as a function of gate voltage increases. This formalism is based on Density Functional Theory and Green's function technique. Our theoretically evaluated results are in good agreement with the experimental data and also with other theoretical workers.

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“…Several recent studies suggested techniques to avoid transport in the presence of IIS have been proposed, such as modulation doping techniques [46,47], or gating the channel materials [48,49,50,51,52,53]. In this way, the high carrier densities can be achieved without the use of direct doping, and the phonon-limited performance would be…”

Section: K Q D mentioning

confidence: 99%

“…An important point we stressed in Ref. [49], is that SRS is not a strong degrading mechanism in channels with feature sizes >10nm, , despite the fact that the gate field tends to shift carriers on the surface. The reason is that the internal electric fields required to achieve charge accumulation are weak (compared to the fields required to achieve inversion layers, for example).…”

Section: K Q D mentioning

confidence: 99%

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

Neophytou

2015

Eur. Phys. J. B

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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...

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Gated Si nanowires for large thermoelectric power factors

Cited by 14 publications

References 30 publications

The influence of non-idealities on the thermoelectric power factor of nanostructured superlattices

The influence of non-idealities on the thermoelectric power factor of nanostructured superlattices

A theoretical study of electron transport through a quantum wire (QW) with a side quantum dots (QD’s) array and quantum point contacts (QPCs) and evaluation of conductance as a function of Fermi energy

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

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