Valley-Engineering Mobilities in Two-Dimensional Materials

Sohier, Thibault; Gibertini, Marco; Campi, Davide; Pizzi, Giovanni; Marzari, Nicola

doi:10.1021/acs.nanolett.9b00865

Cited by 34 publications

(29 citation statements)

References 68 publications

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“…The electron mobility of Ba 2 AuSb is the smallest, in line with its highest scattering rates, as shown in Figure b. Previous studies have clarified that the mobility is significantly affected by the band structure characterized by the effective mass around band edges and the energy difference between different valleys . As shown in Figure c, for Ba 2 AuSb, the electron‐effective mass is the heaviest and the energy difference between conduction valleys is the smallest, which results in the low velocity, high scattering phase space, and earlier appearance of intervalley scattering.…”

supporting

confidence: 51%

“…Previous studies have clarified that the mobility is significantly affected by the band structure characterized by the effective mass around band edges and the energy difference between different valleys. [16,18,35] As shown in Figure 1c, for Ba 2 AuSb, the electroneffective mass is the heaviest and the energy difference between conduction valleys is the smallest, which results in the low velocity, high scattering phase space, and earlier appearance of intervalley scattering. Analogously, the hole mobility of Ba 2 AuBi is the highest due to its small effective mass and large valley gaps.…”

Section: Jinlong Ma Arun S Nissimagoudar Shudong Wang and Wu Li*mentioning

confidence: 98%

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High Thermoelectric Figure of Merit of Full‐Heusler Ba₂AuX (X = As, Sb, and Bi)

Nissimagoudar

Wang

et al. 2020

Physica Rapid Research Ltrs

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Developing high-performance thermoelectric materials is at the core of thermoelectrics, which is the simplest technology applicable to direct green heat-to-electricity energy conversion. To achieve a high conversion efficiency, gauged by the figure of merit ZT ¼ S 2 σT κ e þκ ph , the materials should simultaneously possess a high electrical conductivity (σ) and Seebeck coefficient (S) but a low thermal conductivity containing contribution from electrons (κ e ) and phonons (κ ph ). The fS, σ, κ e g are inversely interdependent such as the increase in σ followed by the decrease in S and increase in κ e ; thus, optimizing ZT is a delicate trade-off between these electrical properties. [1] In contrast, κ ph is relatively decoupled. Therefore, one of the mainstream strategies for high ZT is searching materials with an intrinsically low κ ph . [2][3][4] From the computational point of view, the solutions of Boltzmann transport equations (BTE) with the phonon-phonon and electron-phonon scattering based on density functional theory (DFT) have enabled accurate parameter-free calculations of κ ph [5][6][7][8][9][10] and {S, σ, κ e }. [11][12][13][14][15][16][17][18][19][20][21] Recent calculations revealed that a series of full-Heusler compounds possess ultralow κ ph and dispersive band structures, [22] which insinuate good promise for the thermoelectric applications. Recently, a high ZT has been demonstrated in Ba 2 AuBi by first-principles calculations. [23] Nonetheless, the spin-orbit coupling (SOC) was not considered, which, however, affects the band structure of Ba 2 AuBi significantly [23] and thus the electrical transport properties would be altered. [16,18] Moreover, the BTE was solved under relaxation time approximation (RTA), which generally underestimates the electrical mobility in polar materials due to the strong coupling of the electrons with longitudinal optical (LO) phonons, i.e., long-range Fröhlich interactions. [15][16][17] Therefore, we carried out first-principles calculations for the thermoelectric properties of Ba 2 AuBi as well as Ba 2 AuSb and Ba 2 AuAs considering the SOC and exact solutions of BTE [11,15,16] and found that all the three Ba 2 AuX have high ZT, due to their low thermal conductivities and promising power factors (PF).The DFT calculations were carried out using Quantum ESPRESSO package, [24] with the full-relativistic norm-conserving pseudopotentials generated by the latest multiprojector ONCVPSP code [25] and the inputs of SG15 pseudopotentials. [26] Generalized gradient approximation in the form of Perdew-Burke-Ernzerhof (PBE) [27] was used for the exchange-correlation functional. Ba 2 AuX has a face-centered cubic crystal structure with Fm3m symmetry (Figure S1, Supporting Information), and the relaxed lattice constants are 8.01, 8.28, and 8.38 Å for Ba 2 AuAs, Ba 2 AuSb, and Ba 2 AuBi, respectively ( Figure S2, Supporting Information). The initial electron energies, phonon frequencies, and electron-phonon coupling interactions were conducted on 8 Â 8 Â 8 k and 4 Â 4 Â 4 q grids....

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supporting

confidence: 51%

Section: Jinlong Ma Arun S Nissimagoudar Shudong Wang and Wu Li*mentioning

confidence: 98%

High Thermoelectric Figure of Merit of Full‐Heusler Ba₂AuX (X = As, Sb, and Bi)

Nissimagoudar

Wang

et al. 2020

Physica Rapid Research Ltrs

View full text Add to dashboard Cite

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“…1) can split the six valleys into four higherenergy and two lower-energy valleys on the armchair axis. On the contrary, if the uniaxial strain is along the armchair direction, only two valleys will be pushed up to higher energy 33 . In the following, we will consider the uniaxial strain along the zigzag direction.…”

Section: Reducing Phonon Scattering By Valley-engineeringmentioning

confidence: 99%

“…In other works, the mobility has been evaluated through the Takagi formula 30 , which takes into account only the Bardeen-Shockley acoustic-deformation-potential (ADP) scattering 31 and neglects all the optical and intervalley phonon scatterings 13,32 . However, many 2D semiconductors have multiple degenerate conduction band valleys, which results in a large phase space for intervalley scatterings and in large scattering rates 19,33 . The inelastic nature of these scattering processes has been already shown to deeply affect the transport in electronic devices 28,34 .…”

Section: Introductionmentioning

confidence: 99%

Dissipative Transport and Phonon Scattering Suppression via Valley Engineering in Single-Layer Antimonene and Arsenene Field-Effect Transistors

Cao,

Wu,

Zhang

et al. 2021

Preprint

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Two-dimensional (2D) semiconductors are promising channel materials for next-generation field-effect transistors (FETs) thanks to their unique mechanical properties and enhanced electrostatic control. However, the performance of these devices can be strongly limited by the scattering processes between carriers and phonons, usually occurring at high rates in 2D materials. Here, we use quantum transport simulations calibrated on first-principle computations to report on dissipative transport in antimonene and arsenene n-type FETs at the scaling limit. We show that the widelyused approximations of either ballistic transport or simple acoustic deformation potential scattering result in large overestimation of the ON current, due to neglecting the dominant intervalley and optical phonon scattering processes. We also propose a strategy to improve the device performance by removing the valley degeneracy and suppressing most of the intervalley scattering channels via an uniaxial strain along the zigzag direction. The method is applicable to other similar 2D semiconductors characterized by multivalley transport.

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“…It is not obvious to further qualify this class as a whole, which hosts a variety of different members. Focusing on intrinsic scattering mechanisms driven by electron-phonon interactions (EPIs), multivalley materials can usually be excluded, since intervalley EPIs are often strong [22,23], and at momenta larger than the size of the Fermi pocket that characterizes the free carriers providing the screening. In this large momentum regime, free-carrier screening is inefficient even if the EPI are sensitive to it.…”

Section: Fröhlich-limited 2d Semiconductorsmentioning

confidence: 99%

Remote free-carrier screening to boost the mobility of Fröhlich-limited two-dimensional semiconductors

Sohier

Gibertini

Verstraete

2021

Phys. Rev. Materials

Self Cite

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Van der Waals heterostructures provide a versatile tool to not only protect or control, but also enhance the properties of a 2D material. We use ab initio calculations and semianalytical models to find strategies which boost the mobility of a current-carrying two-dimensional (2D) semiconductor within a heterostructure. Free-carrier screening from a metallic "screener" layer remotely suppresses electron-phonon interactions in the currentcarrying layer. This concept is most effective in 2D semiconductors whose scattering is dominated by screenable electron-phonon interactions, and in particular, the Fröhlich coupling to polar-optical phonons. Such materials are common and characterized by overall low mobilities in the small doping limit and much higher ones when the 2D material is doped enough for electron-phonon interactions to be screened by its own free carriers. We use GaSe as a prototype and place it in a heterostructure with doped graphene as the "screener" layer and boron nitride as a separator. We develop an approach to determine the electrostatic response of any heterostructure by combining the responses of the individual layers computed within density functional perturbation theory. Remote screening from graphene can suppress the long-wavelength Fröhlich interaction, leading to a consistently high mobility around 500-600 cm 2 /V s for carrier densities in GaSe from 10 11 to 10 13 cm −2 . Notably, the low-doping mobility is enhanced by a factor 2.5. This remote free-carrier screening is more efficient than more conventional manipulation of the dielectric environment, and it is most effective when the separator (boron nitride) is thin.

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Valley-Engineering Mobilities in Two-Dimensional Materials

Cited by 34 publications

References 68 publications

High Thermoelectric Figure of Merit of Full‐Heusler Ba₂AuX (X = As, Sb, and Bi)

High Thermoelectric Figure of Merit of Full‐Heusler Ba₂AuX (X = As, Sb, and Bi)

Dissipative Transport and Phonon Scattering Suppression via Valley Engineering in Single-Layer Antimonene and Arsenene Field-Effect Transistors

Remote free-carrier screening to boost the mobility of Fröhlich-limited two-dimensional semiconductors

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Valley-Engineering Mobilities in Two-Dimensional Materials

Cited by 34 publications

References 68 publications

High Thermoelectric Figure of Merit of Full‐Heusler Ba2AuX (X = As, Sb, and Bi)

High Thermoelectric Figure of Merit of Full‐Heusler Ba2AuX (X = As, Sb, and Bi)

Dissipative Transport and Phonon Scattering Suppression via Valley Engineering in Single-Layer Antimonene and Arsenene Field-Effect Transistors

Remote free-carrier screening to boost the mobility of Fröhlich-limited two-dimensional semiconductors

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Product

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High Thermoelectric Figure of Merit of Full‐Heusler Ba₂AuX (X = As, Sb, and Bi)

High Thermoelectric Figure of Merit of Full‐Heusler Ba₂AuX (X = As, Sb, and Bi)