Giant enhancement of <i>n</i>-type carrier mobility in highly strained germanium nanostructures

Murphy-Armando, Felipe; Fahy, Stephen

doi:10.1063/1.3590334

Cited by 42 publications

(50 citation statements)

References 24 publications

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“…Given a certain material system, the maximum zT achieved by carrier density tuning would be further increased if the deformation potential of bands participating in carrier transport could be engineered. The latter has been shown possible at least in low dimensional systems: Murphy-Armando and Fahy (43) found that the deformation potential of Γ band of n-type Ge film is decreased with strain. Also, in Si thin films embedded between hard layers of diamond (44), the mobility is found increased due to suppressed deformation potential electron-phonon scattering.…”

Section: Shanghai Institute Of Ceramics-chinese Academy Of Sciences mentioning

confidence: 99%

Weak electron–phonon coupling contributing to high thermoelectric performance in n-type PbSe

Wang

Pei

LaLonde

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

378

365

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PbSe is a surprisingly good thermoelectric material due, in part, to its low thermal conductivity that had been overestimated in earlier measurements. The thermoelectric figure of merit, zT, can exceed 1 at high temperatures in both p-type and n-type PbSe, similar to that found in PbTe. While the p-type lead chalcogenides (PbSe and PbTe) benefit from the high valley degeneracy (12 or more at high temperature) of the valence band, the n-type versions are limited to a valley degeneracy of 4 in the conduction band. Yet the n-type lead chalcogenides achieve a zT nearly as high as the p-type lead chalcogenides. This effect can be attributed to the weaker electron-phonon coupling (lower deformation potential coefficient) in the conduction band as compared with that in the valence band, which leads to higher mobility of electrons compared to that of holes. This study of PbSe illustrates the importance of the deformation potential coefficient of the charge-carrying band as one of several key parameters to consider for band structure engineering and the search for high performance thermoelectric materials.energy | semiconductor | quality factor W aste heat recovery using thermoelectric power generation is attracting considerable interest from the automobile industry (1) as well as from many other areas (2). Large-scale production of bulk materials with high figure of merit, zT, defined as zT ¼ S 2 σT∕ðκ e þ κ L Þ (S is the Seebeck coefficient, σ is the electric conductivity, and κ e and κ L are the electronic and lattice thermal conductivity, respectively), is the key to widespread adaption of thermoelectric technology. The search for good thermoelectric materials has focused on investigating semiconductors that have suitable band structures and low thermal conductivities (3, 4). As one of the first investigated material systems (5), PbTe and its alloys have been extensively studied and remain some of the best (6, 7) thermoelectric materials for applications from 500 to 900 K. Considerable effort has been made to achieve a higher zT in these alloys by reducing the lattice thermal conductivity, κ L , by incorporation of nanometer scale inclusions (8-11). Other strategies approach the challenge of increasing zT from different angles, such as band structure distortion by Tl doping (12), and more recently, increasing band degeneracy by converging two different valence bands in p-type PbTe (13).It can be shown that the material parameter called the thermoelectric quality factor, B,determines the optimized figure of merit (14-16) (N V is the band degeneracy, m Ã b is the density of states effective mass of a single band, μ 0 is the mobility at nondegenerate limit, and κ L is the lattice thermal conductivity). This expression is derived for semiconductors with single band transport behavior where the carrier concentration can be optimized to achieve maximum zT. For good thermoelectric semiconductors the dominant scattering mechanism at high temperatures, where zT peaks, is typically due to acoustic phonons. The deformation pote...

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Section: Shanghai Institute Of Ceramics-chinese Academy Of Sciences mentioning

confidence: 99%

Weak electron–phonon coupling contributing to high thermoelectric performance in n-type PbSe

Wang

Pei

LaLonde

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

378

365

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“…14 We have also included in our analysis the effects of strains on the C band, which have been treated elswhere. 15 …”

Section: Bands and Strainmentioning

confidence: 99%

First principles calculation of electron-phonon and alloy scattering in strained SiGe

Murphy-Armando

Fahy

2011

Journal of Applied Physics

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First-principles electronic structure methods are used to predict the mobility of n-type carrier scattering in strained SiGe. We consider the effects of strain on the electron-phonon deformation potentials and the alloy scattering parameters. We calculate the electron-phonon matrix elements and fit them up to second order in strain. We find, as expected, that the main effect of strain on mobility comes from the breaking of the degeneracy of the six Δ and L valleys, and the choice of transport direction. The non-linear effects on the electron-phonon coupling of the Δ valley due to shear strain are found to reduce the mobility of Si-like SiGe by 50% per % strain. We find increases in mobility between 2 and 11 times that of unstrained SiGe for certain fixed Ge compositions, which should enhance the thermoelectric figure of merit in the same order, and could be important for piezoresistive applications

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“…At the same time, ab initio calculations provide an effective tool to estimate electron-phonon coupling strength in metals [10][11][12] and semimetals like graphene [13][14][15][16] or bismuth 17,18 . In the case of semiconductors, the predictive capability of calculations based on density functional perturbation theory (DFPT) 19,20 for the electronphonon matrix elements has been demonstrated in a number of semiconductors [21][22][23] , alloys 24,25 and nanostructures 23,26 . Recently, a method to interpolate the electron-phonon coupling matrix elements using Wannier fuctions has been introduced 11,27,28 , providing a computationally efficient method to calculate electron-phonon matrix elements on extremely fine grids in the Brillouin zone (BZ) of metals.…”

Section: Introductionmentioning

confidence: 99%

Wannier interpolation of the electron-phonon matrix elements in polar semiconductors: Polar-optical coupling in GaAs

et al. 2015

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We generalize the Wannier interpolation of the electron-phonon matrix elements to the case of polar-optical coupling in polar semiconductors. We verify our methodological developments against experiments, by calculating the widths of the electronic bands due to electron-phonon scattering in GaAs, the prototype polar semiconductor. The calculated widths are then used to estimate the broadenings of excitons at critical points in GaAs and the electron-phonon relaxation times of hot electrons. Our findings are in good agreement with available experimental data. Finally, we demonstrate that while the Fröhlich interaction is the dominant scattering process for electrons/holes close to the valley minima, in agreement with low-field transport results, at higher energies, the intervalley scattering dominates the relaxation dynamics of hot electrons or holes. The capability of interpolating the polar-optical coupling opens new perspectives in the calculation of optical absorption and transport properties in semiconductors and thermoelectrics.

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Giant enhancement of n-type carrier mobility in highly strained germanium nanostructures

Cited by 42 publications

References 24 publications

Weak electron–phonon coupling contributing to high thermoelectric performance in n-type PbSe

Weak electron–phonon coupling contributing to high thermoelectric performance in n-type PbSe

First principles calculation of electron-phonon and alloy scattering in strained SiGe

Wannier interpolation of the electron-phonon matrix elements in polar semiconductors: Polar-optical coupling in GaAs

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