Structural Properties of Heavily B-Doped SiGe Thin Films for High Thermoelectric Power

Takiguchi, Hiroaki; Matoba, Akinari; Sasaki, Kyuro; Okamoto, Yoshio; Miyazaki, Hisashi; Morimoto, Jun

doi:10.2320/matertrans.e-m2010806

Cited by 25 publications

(20 citation statements)

References 13 publications

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“…The low electrical resistivity observed in the annealed sample along with its large | S | lead to a remarkably high power factor that reaches PF ≈ 15 μW cm −1 K −2 at 300 K. This value is nearly five times larger than the reported value for optimized bulk CrN at the same temperature and comparable to the high temperature value observed in ScN and other commercial thermoelectric materials, such as B‐doped SiGe (PF ≈ 19 μW cm −1 K −2 ), and La 3 Te 4− x Pb x (PF ≈ 14 μW cm −1 K −2 at 1100 K) . The combination of this large PF and the intrinsically low thermal conductivity in RS–CrN results in a high zT = 0.12 at room temperature for the annealed sample (Figure d), which is a value similar to that shown in other state‐of‐the‐art thermoelectric materials at the same temperature .…”

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confidence: 57%

Epitaxial CrN Thin Films with High Thermoelectric Figure of Merit

et al. 2015

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The design of efficient thermoelectric (TE) devices for energy harvesting and advanced cooling applications is one of the current challenges in materials science. [1] So far, the most common materials used in commercial TE devices are rock-salt IV-VI (PbTe, PbSe) and distorted rock-salt V2-VI3 (Bi2Te3, Bi2Se3) semiconductors. [2] One of the key factors behind the high TE performance of these materials is their abnormally low lattice thermal conductivity (κl), 2 which is one of the fundamental parameters that define the dimensionless TE figure of merit zT = S 2 σT/(κl+κe), in which S is the Seebeck coefficient, σ the electrical conductivity, T the absolute temperature, and κe the electronic thermal conductivity.In a recent paper, Lee et al. [3] suggested that the main reason for the low lattice thermal conductivity in rock-salt IV-VI compounds is the resonant bonding (RB) effect: the p-orbitals with 3 electrons per atom cannot form the six saturated bonds of the rock-salt lattice, and therefore an RB structure is established. [ 4 ] Using first-principles calculations, they demonstrated that the large electronic polarizability of the resonant bonds introduces long-range interactions and a softening of the transverse optical phonon mode. This ultimately causes acoustic phonon scattering and is responsible for the low lattice thermal conductivity in IV-VI and V2-VI3 compounds. An interesting question is whether or not the concept of RB can be extrapolated to transition-metal (TM) compounds with a rock-salt structure. The versatility of the oxidation states and ionic sizes shown by TM ions would offer enormous possibilities for tuning their TE properties, which would allow for new approaches regarding the design of TE materials with improved capabilities.In this communication we demonstrate that rock-salt CrN shows intrinsic lattice instabilities that suppress its thermal conductivity. Using ab-initio calculations, we determined that the origin of these instabilities is similar to that observed in IV-VI compounds with RB states. [3,5] Through the fabrication of high quality epitaxial (001) CrN thin films we report a 250% increase in the zT at room temperature compared to bulk CrN. [6] These results along with its high thermal stability, resistance to corrosion, and exceptional mechanical properties, make CrN a promising n-type material for high-temperature TE applications.The presence of extrinsic factors, such as N-vacancies or epitaxial constrains, are likely behind the large variety of structural and transport properties previously reported for CrN films. [7] In the case of polycrystalline bulk CrN, the intergrain contribution to the electrical and 3 thermal conductivities can be significant enough to mask its intrinsic transport properties and, ultimately, its thermoelectric performance. Therefore, in order to access the intrinsic thermoelectric properties of CrN, it is necessary to develop the fabrication of epitaxial, stoichiometric, and fully relaxed CrN films. The results discussed in this pap...

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confidence: 57%

Epitaxial CrN Thin Films with High Thermoelectric Figure of Merit

et al. 2015

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“…Later research by Burmistrova et al 16 have improved the power factor values to ~ (3.3-3.5) 10 -3 W/m-K 2 at 600-850K in sputter-deposited n-type ScN thin films grown on MgO substrates. These power factors at 600-850K temperature ranges are higher than those of Bi 2 Te 3 and its alloys at 400 K 2,8 , as well as the best high-temperature thermoelectric materials such as La 3 Te 4 32 at 600 K, and compare well with undoped crystalline SiGe 33 in the same temperature range. The origin of such large power factors can be explained by the changes in ScN's electronic structure with respect to the presence of point defects and impurities (such as Sc and N vacancies 34 , and doping effects of O and C on N-sites, and Ca and Ti on Sc sites on ScN's electronic structure 35 ).…”

Section: The Efficiency Of a Thermoelectric Materials Is Represented Bmentioning

confidence: 86%

Temperature-dependent thermal and thermoelectric properties of n -type and p -type Sc1−x
Saha
¹
,
Taborda²,
Bahk
³

et al. 2018
Phys. Rev. B
37
1
22
1
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Scandium Nitride (ScN) is an emerging rocksalt semiconductor with octahedral coordination, and an indirect bandgap. ScN has attracted significant attention in recent years for its potential thermoelectric applications, as a component material in epitaxial metal/semiconductor superlattices, and as a substrate for defect-free GaN growth. Sputter-deposited ScN thin films are highly degenerate n-type semiconductors, and exhibit a large thermoelectric power factor of ~3.5 10-3 W/m-K 2 at 600K-800K. Since practical thermoelectric devices require both n-and p-type materials with high thermoelectric figures-of-merit, development and demonstration of highly efficient p-type ScN is extremely important. Recently, the authors have demonstrated p-type Sc 1x Mg x N thin film alloys with low Mg x N y mole-fractions within the ScN matrix. In this article, we demonstrate temperature dependent thermal and thermoelectric transport properties, including large thermoelectric power factors in both n-and p-type Sc 1-x Mg x N thin film alloys at high temperatures (up to 850K). Employing a combination of temperature dependent Seebeck coefficient, electrical conductivity and thermal conductivity measurements, as well as detailed Boltzmann transport based modeling analyses of the transport properties, we demonstrate that ptype Sc 1-x Mg x N thin film alloys exhibit a maximum thermoelectric power factor of ~0.8 10-3 W/m-K 2 at 850K. The thermoelectric properties are tunable by adjusting the Mg x N y molefraction inside the ScN matrix, thereby shifting the Fermi energy in the alloy films from inside the conduction band in case of undoped n-type ScN to inside the valence band in highly holedoped p-type Sc 1-x Mg x N thin film alloys. The thermal conductivities of both the n-and p-type films were found to be undesirably large for thermoelectric applications. Thus, future work should address strategies to reduce the thermal conductivity of Sc 1-x Mg x N thin-film alloys, without affecting the power factor for improved thermoelectric performance.

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“…Unfortunately, in the experiment conducted by Takiguchi et al [8], when they attempted to make Si/(Ge + B) superlattice thin film, there was no sign of the MIC effect. In fact, high thermoelectric power (>1 mVK −1 ) was observed in the superlattice thin film only when nanocrystals with a diameter less than 10 nm were present; however, limitations of the specimen preparation system and the use of B as the dopant made it difficult to prepare specimens with a precisely controlled nanostructure.…”

Section: Introductionmentioning

confidence: 99%

“…MIC is a phenomenon whereby dopant metal atoms lower the recrystallization temperature of an amorphous semiconductor [7]. This suggests that superior thermoelectric properties will arise from the nanocrystals in the amorphous matrix [8,9].…”

Section: Introductionmentioning

confidence: 99%

The Relationship between Nanocluster Precipitation and Thermal Conductivity in Si/Ge Amorphous Multilayer Films: Effects of Cu Addition

Tamidi

Sasajima

2016

Journal of Nanomaterials

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We have used a molecular dynamics technique to simulate the relationship between nanocluster precipitation and thermal conductivity in Si/Ge amorphous multilayer films, with and without Cu addition. In the study, the Green-Kubo equation was used to calculate thermal conductivity in these materials. Five specimens were prepared: Si/Ge layers, Si/(Ge + Cu) layers, (Si + Cu)/(Ge + Cu) layers, Si/Cu/Ge/Cu layers, and Si/Cu/Ge layers. The number of precipitated nanoclusters in these specimens, which is defined as the number of four-coordinate atoms, was counted along the lateral direction of the specimens. The observed results of precipitate formation were considered in relation to the thermal conductivity results. Enhancement of precipitation of nanoclusters by Cu addition, that is, densification of four-coordinate atoms, can prevent the increment of thermal conductivity. Cu dopant increases the thermal conductivity of these materials. Combining these two points, we concluded that Si/Cu/Ge is the best structure to improve the conversion efficiency of the Si/Ge amorphous multilayer films.

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Structural Properties of Heavily B-Doped SiGe Thin Films for High Thermoelectric Power

Cited by 25 publications

References 13 publications

Epitaxial CrN Thin Films with High Thermoelectric Figure of Merit

Epitaxial CrN Thin Films with High Thermoelectric Figure of Merit

Temperature-dependent thermal and thermoelectric properties of n -type and p -type Sc1−x
Saha
¹
,
Taborda²,
Bahk
³

et al. 2018
Phys. Rev. B
37
1
22
1
View full text Add to dashboard Cite

The Relationship between Nanocluster Precipitation and Thermal Conductivity in Si/Ge Amorphous Multilayer Films: Effects of Cu Addition

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Structural Properties of Heavily B-Doped SiGe Thin Films for High Thermoelectric Power

Cited by 25 publications

References 13 publications

Epitaxial CrN Thin Films with High Thermoelectric Figure of Merit

Epitaxial CrN Thin Films with High Thermoelectric Figure of Merit

Temperature-dependent thermal and thermoelectric properties of n -type and p -type Sc1−xSaha1, Taborda2, Bahk3 et al. 2018Phys. Rev. B371221View full textAdd to dashboardCite

The Relationship between Nanocluster Precipitation and Thermal Conductivity in Si/Ge Amorphous Multilayer Films: Effects of Cu Addition

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Temperature-dependent thermal and thermoelectric properties of n -type and p -type Sc1−x
Saha
¹
,
Taborda²,
Bahk
³

et al. 2018
Phys. Rev. B
37
1
22
1
View full text Add to dashboard Cite