Unexpected Large Hole Effective Masses in SnSe Revealed by Angle-Resolved Photoemission Spectroscopy

SnSe is a promising thermoelectric material with record-breaking figure of merit. However, to date a comprehensive understanding of the electronic structure and most critically, the self-hole-doping mechanism in SnSe is still absent. Here we report the highly anisotropic electronic structure of SnSe investigated by angle-resolved photoemission spectroscopy, in which a unique pudding-mould-shaped valence band with quasi-linear energy dispersion is revealed. We prove that p-type doping in SnSe is extrinsically controlled by local phase segregation of SnSe2 microdomains via interfacial charge transferring. The multivalley nature of the pudding-mould band is manifested in quantum transport by crystallographic axis-dependent weak localisation and exotic non-saturating negative magnetoresistance. Strikingly, quantum oscillations also reveal 3D Fermi surface with unusual interlayer coupling strength in p-SnSe, in which individual monolayers are interwoven by peculiar point dislocation defects. Our results suggest that defect engineering may provide versatile routes in improving the thermoelectric performance of the SnSe family.

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“…Note added. We have noticed that there are two other ARPES papers on p-SnSe published very recently 33 , 34 , during the revision of our work.…”

Section: Discussionmentioning

confidence: 89%

Defects controlled hole doping and multivalley transport in SnSe single crystals

et al. 2018

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“…The significant thermoelectric performance also raised from high S 2 (~14.2 μW cm -1 K -2 ), which came from high (~149.5 S cm -1 ) and strongly enhanced S (~307.8 μV K -1 ) at 773 K [78]. By angle-resolved photoemission spectroscopy, large hole effective masses were revealed in both undoped and hole-doped SnSe crystals [243], contributing to the high electrical transport…”

Section: P-type Dopingmentioning

confidence: 98%

High-performance SnSe thermoelectric materials: Progress and future challenge

Chen

Zhao

Zou

2018

Progress in Materials Science

Self Cite

465

410

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Thermoelectric materials offer an alternative opportunity to tackle the energy crisis and environmental problems by enabling the direct solid-state energy conversion. As a promising candidate with full potentials for the next generation thermoelectrics, tin selenide (SnSe) and its associated thermoelectric materials have been attracted extensive attentions due to their ultralow thermal conductivity and high electrical transport performance (power factor). To provide a thorough overview of recent advances in SnSe-based thermoelectric materials that have been revealed as promising thermoelectric materials since 2014, here, we first focus on the inherent relationship between the structural characteristics and the supreme thermoelectric performance of SnSe, including the thermodynamics, crystal structures, and electronic structures. The effects of phonon scattering, pressure or strain, and oxidation behavior on the thermoelectric performance of SnSe are discussed in detail. Besides, we summarize the current theoretical calculations to predict and understand the thermoelectric performance of SnSe, and provide a comprehensive summary on the current synthesis, characterization, and thermoelectric performance of both SnSe crystals and polycrystals, and their associated materials. In the end, we point out the controversies, challenges and strategies toward future enhancements of the SnSe thermoelectric materials.

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“…Tin selenide (SnSe) is a typical semiconductor with a narrow bandgap of ≈0.9 eV, making it a good candidate with great potentials for applications in low‐cost thermoelectrics . A remarkable high peak ZT of ≈2.6 at 923 K was reported in the p‐type SnSe single crystals, and a relative high ZT of ≈2.2 at 773 K was also achieved from the n‐type Bi‐doped SnSe single crystals, both along their b ‐axes.…”

Section: Introductionmentioning

confidence: 99%

Realizing High Thermoelectric Performance in n‐Type Highly Distorted Sb‐Doped SnSe Microplates via Tuning High Electron Concentration and Inducing Intensive Crystal Defects

Shi

Zheng

Liu

et al. 2018

Advanced Energy Materials

128

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figure of merit (ZT) is defined as ZT = S 2 σT/κ = S 2 σT/(κ e +κ l ), where S, σ, κ, κ e , κ l , and T are the Seebeck coefficient, the electrical conductivity, the total thermal conductivity, the electrical thermal conductivity, the lattice thermal conductivity, and the absolute temperature, respectively. [3,5] A high powder factor (S 2 σ) and a low κ are required to achieve a high ZT value. [6][7][8] So far, significant efforts have been devoted to enhancing S 2 σ and/or reduce κ. [9] For the strategies of achieving high S 2 σ, resonant state doping, [10][11][12] band converging, [13][14][15][16] minority carrier blocking, [17,18] and quantum confinement [19][20][21] were designed and developed. For reducing κ, the strategies of nanostructuring, [22][23][24][25] hierarchical architecturing, [26][27][28] and nanoprecipitate inducing [29][30][31] were successfully adopted.Tin selenide (SnSe) is a typical semiconductor with a narrow bandgap of ≈0.9 eV, [32][33][34] making it a good candidate with great potentials for applications in low-cost thermoelectrics. [35][36][37] A remarkable high peak ZT of ≈2.6 at 923 K was reported in the p-type SnSe single crystals, [38] and a relative high ZT of ≈2.2 at 773 K was also achieved from the n-type Bi-doped SnSe single crystals, [39] both along their b-axes. Such high ZT values come from their ultralow κ (both <0.3 W m −1 K −1 at 773 K). [38,39] However, suffered from their poor mechanical properties, rigid crystal growth conditions, and high production cost, SnSe single crystals are difficult to be employed in practical thermoelectric devices, and the techniques used for growing single crystals are limited for repeatable and industrial scale-up. [40] To overcome these challenges, polycrystalline SnSe has become a research topic. To synthesize polycrystalline SnSe, various methods have been explored, such as melting, [40][41][42] arc-melting, [43,44] mechanical alloying, [45][46][47] solid state reaction, [48][49][50] and hydrothermal, [51][52][53] or solvothermal methods. [54,55] To achieve a high ZT, texturing and doping have been two key approaches to enhance S 2 σ and/or reduce κ, from which the ZT values have been improved from 0.1 to ≈1.7 (p-type), although such ZT values are still much lower than their single crystal counterparts due to their relatively high κ and low S 2 σ. [52,[56][57][58][59][60] Considering the requirement of both p-type and n-type thermoelectric materials for composing the thermoelectric In this study, a record high figure of merit (ZT) of ≈1.1 at 773 K is reported in n-type highly distorted Sb-doped SnSe microplates via a facile solvothermal method. The pellets sintered from the Sb-doped SnSe microplates show a high power factor of ≈2.4 µW cm −1 K −2 and an ultralow thermal conductivity of ≈0.17 W m −1 K −1 at 773 K, leading a record high ZT. Such a high power factor is attributed to a high electron concentration of 3.94 × 10 19 cm −3 via Sb-enabled electron doping, and the ultralow thermal conductivity derives from the enhanced phonon scatter...

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Unexpected Large Hole Effective Masses in SnSe Revealed by Angle-Resolved Photoemission Spectroscopy

Cited by 50 publications

References 45 publications

Defects controlled hole doping and multivalley transport in SnSe single crystals

Defects controlled hole doping and multivalley transport in SnSe single crystals

High-performance SnSe thermoelectric materials: Progress and future challenge

Realizing High Thermoelectric Performance in n‐Type Highly Distorted Sb‐Doped SnSe Microplates via Tuning High Electron Concentration and Inducing Intensive Crystal Defects

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