Effects of impurities on the lattice dynamics of nanocrystalline silicon for thermoelectric application

Claudio, Tania; Schierning, Gabi; Theissmann, Ralf; Wiggers, Hartmut; Schober, H.; Koza, Michael Marek; Hermann, Raphaël P.

doi:10.1007/s10853-012-6827-y

Cited by 25 publications

(27 citation statements)

References 39 publications

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“…) using its low‐energy limit

L_{D} = lim_{E \to 0} false[g false(E false) / E^{2} false]

and

v_{s}^{3} = η / 2 π^{2} N_{V} ℏ^{3} L_{D}

(), where

N_{V}

is the number of atoms per unit volume (

N_{V} = ρ N_{A} / M_{w}

with

ρ

being the density,

N_{A}

the Avogadro number, and

M_{w}

the atomic weight) and

η

is a scaling factor taking into account the different atomic masses and neutron scattering cross‐sections of Si, Ge, and P (

η \approx 1.1

in the present case). The speed of sound obtained by this method is 3.89(2) km s

^{- 1}

, i.e., nanostructuring combined with a 20% substitution of Si atoms by Ge atoms causes a decrease by

\approx

42% of the speed of sound of bulk Si (6.73(5) km s

^{- 1}

) obtained by the same method (). This decrease is significantly higher than can be accounted for only by the density increase upon alloying.…”

Section: Resultsmentioning

confidence: 81%

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Lattice dynamics and thermoelectric properties of nanocrystalline silicon–germanium alloys

Claudio

Stein

Petermann

et al. 2015

Physica Status Solidi (a)

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The lattice dynamics and thermoelectric properties of sintered phosphorus‐doped nanostructured silicon–germanium alloys obtained by gas‐phase synthesis were studied. Measurements of the density of phonon states by inelastic neutron scattering were combined with measurements of the elastic constants and the low‐temperature heat capacity. A strong influence of nanostructuring and alloying on the lattice dynamics was observed. The thermoelectric transport properties of samples with different doping as well as samples sintered at different temperature were characterized between room temperature and 1000°C. A peak figure of merit italiczT=0.88 at 900°C is observed and is comparatively insensitive to the aforementioned parameter variations.

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“…) using its low‐energy limit

L_{D} = lim_{E \to 0} false[g false(E false) / E^{2} false]

and

v_{s}^{3} = η / 2 π^{2} N_{V} ℏ^{3} L_{D}

(), where

N_{V}

is the number of atoms per unit volume (

N_{V} = ρ N_{A} / M_{w}

with

ρ

being the density,

N_{A}

the Avogadro number, and

M_{w}

the atomic weight) and

η

is a scaling factor taking into account the different atomic masses and neutron scattering cross‐sections of Si, Ge, and P (

η \approx 1.1

in the present case). The speed of sound obtained by this method is 3.89(2) km s

^{- 1}

, i.e., nanostructuring combined with a 20% substitution of Si atoms by Ge atoms causes a decrease by

\approx

42% of the speed of sound of bulk Si (6.73(5) km s

^{- 1}

) obtained by the same method (). This decrease is significantly higher than can be accounted for only by the density increase upon alloying.…”

Section: Resultsmentioning

confidence: 81%

“…a and b) and energy‐dispersive X‐ray spectroscopy (EDX) gave indications that those precipitates are oxides. However, any significant amorphous

{SiO}_{2}

impurity would result () in a strong increase of the specific heat at 10 K as well as in a Boson peak visible in the DPS. As these fingerprints are absent or below detection limit (see Figs.…”

Section: Resultsmentioning

confidence: 99%

Lattice dynamics and thermoelectric properties of nanocrystalline silicon–germanium alloys

Claudio

Stein

Petermann

et al. 2015

Physica Status Solidi (a)

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“…At the lowest temperatures, a simple model of the heat capacity can be designed by considering an electronic contribution (gT) and a lattice contribution that can be described using the Debye model and an Einstein term to describe the excess C p at approximately 45 K: 25 C p (T) = gT + dC D (T) + eC E (T) (1) where d and e are prefactors for the Debye and Einstein contributions, C D (T) and C E (T), respectively. More details about the Debye and Einstein models can be found in ref.…”

Section: Lattice Dynamicsmentioning

confidence: 99%

Nanocrystalline silicon: lattice dynamics and enhanced thermoelectric properties

Claudio

Stein

Stroppa

et al. 2014

Phys. Chem. Chem. Phys.

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Silicon has several advantages when compared to other thermoelectric materials, but until recently it was not used for thermoelectric applications due to its high thermal conductivity, 156 W K(-1) m(-1) at room temperature. Nanostructuration as means to decrease thermal transport through enhanced phonon scattering has been a subject of many studies. In this work we have evaluated the effects of nanostructuration on the lattice dynamics of bulk nanocrystalline doped silicon. The samples were prepared by gas phase synthesis, followed by current and pressure assisted sintering. The heat capacity, density of phonons states, and elastic constants were measured, which all reveal a significant, ≈25%, reduction in the speed of sound. The samples present a significantly decreased lattice thermal conductivity, ≈25 W K(-1) m(-1), which, combined with a very high carrier mobility, results in a dimensionless figure of merit with a competitive value that peaks at ZT≈ 0.57 at 973 °C. Due to its easily scalable and extremely low-cost production process, nanocrystalline Si prepared by gas phase synthesis followed by sintering could become the material of choice for high temperature thermoelectric generators.

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“…Instead, the temperature dependant measurements suggest a frequency‐dependent model in which the MFP for phonon‐boundary scattering is inversely proportional to the phonon frequency. The nanocrystalline nature of the bulk further directly affects the phonon dispersion relation which is altered by the introduction of interfaces into the material, as was demonstrated for nanocrystalline silicon (with considerable oxygen impurites) by Claudio et al .…”

Section: Silicon As a Thermoelectric Materialsmentioning

confidence: 97%

Silicon nanostructures for thermoelectric devices: A review of the current state of the art

Schierning

2014

Physica Status Solidi (a)

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102

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Silicon is the most important element of modern semiconductor industry. As a thermoelectric converter material, it would be able to promote applications dramatically since device integration and scaling of the fabrication processes could be borrowed from existing technology. Though the thermoelectric performance of single crystalline silicon is only poor, silicon nanostructures have demonstrated a competitive figure of merit. To make use of these nanostructures, novel device architectures are necessary. This review provides an overview over the physical background of silicon as thermoelectric converter material as well as different nanostructures like nanowires, porous nanomeshes, and nanocrystalline bulk and their thermoelectric properties, focusing mostly on experimental data. Further, different thermoelectric converter device concepts including nanowire device concepts, pn junction thermoelectric generators and integrated spot coolers are discussed and their realization with silicon nanostructures briefly sketched. (a) Nanowires, porous nanomeshes and nanocrystalline bulk with promising thermoelectric material's figure of merit. (b) Innovative device concepts using nanowires or large area pn junctions for thermoelectric heat‐to‐electricity conversion.

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Effects of impurities on the lattice dynamics of nanocrystalline silicon for thermoelectric application

Cited by 25 publications

References 39 publications

Lattice dynamics and thermoelectric properties of nanocrystalline silicon–germanium alloys

Lattice dynamics and thermoelectric properties of nanocrystalline silicon–germanium alloys

Nanocrystalline silicon: lattice dynamics and enhanced thermoelectric properties

Silicon nanostructures for thermoelectric devices: A review of the current state of the art

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