Giant piezoresistance in silicon-germanium alloys

Murphy-Armando, Felipe; Fahy, Stephen

doi:10.1103/physrevb.86.035205

Cited by 12 publications

(12 citation statements)

References 28 publications

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“…The results given by this k.p approach vs using the band structure from DFT and GW calculations are almost identical to our previous results for alloy and phonon-limited transport. [18][19][20]23 Also, other groups are following similar k.p approaches to interpolate the DFT generated band structure 24 to ease the integration of thermoelectric properties. 25 The integration of Eq.…”

Section: Methodsmentioning

confidence: 99%

“…Interest in strained SiGe is due to its importance in enhancing the mobility in transistor channels and its use as sensitive piezo-resistive sensors. 47,48 Regarding thermoelectric effects, strain has the potential to increase the figure of merit, via the enhancement of the electrical mobility. Strain also strongly affects the thermopower, often counterbalancing the effects on the mobility.…”

Section: A Comparison To Experimentsmentioning

confidence: 99%

“…Most of the scattering parameters used in this work can be found in the literature. In our previous work, we calculated from first principles the scattering by alloy disorder 16,17 and electron-phonon scattering 18,23 . We also calculated the effect of strain in these parameters.…”

Section: Fig 2 Energy Gap Between the E ∆ 3vmentioning

confidence: 99%

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Enhancement of the electronic thermoelectric properties of bulk strained silicon-germanium alloys using the scattering relaxation times from first-principles calculations

Murphy-Armando

2019

Journal of Applied Physics

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We use first-principles electronic structure methods to calculate the electronic thermoelectric properties (i.e. due to electronic transport only) of single-crystalline bulk n-type silicon-germanium alloys vs Ge composition, temperature, doping concentration and strain. We find excellent agreement to available experiments for the resistivity, mobility and Seebeck coefficient. These results are combined with the experimental lattice thermal conductivity to calculate the thermoelectric figure of merit ZT , finding very good agreement with experiment. We predict that 3% tensile hydrostatic strain enhances the n-type ZT by 50% at carrier concentrations of n = 10 20 cm −3 and temperature of T = 1200K. These enhancements occur at different alloy compositions due to different effects: at 50% Ge composition the enhancements are achieved by a strain induced decrease in the Lorenz number, while the power factor remains unchanged. These characteristics are important for highly doped and high temperature materials, in which up to 50% of the heat is carried by electrons. At 70% Ge the increase in ZT is due to a large increase in electrical conductivity produced by populating the high mobility Γ conduction band valley, lowered in energy by strain.

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Section: Methodsmentioning

confidence: 99%

Section: A Comparison To Experimentsmentioning

confidence: 99%

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Enhancement of the electronic thermoelectric properties of bulk strained silicon-germanium alloys using the scattering relaxation times from first-principles calculations

Murphy-Armando

2019

Journal of Applied Physics

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“…The influence of Ge content on the gauge factor of SiGe alloys has been recently investigated by Murphy-Armando and Fahy using first-principles calculations [8]. Here, the authors show that electronic inter-valley scattering plays a mayor role in order to enhance the gauge factor.…”

Section: Introductionmentioning

confidence: 94%

Valence band structure engineering of thin SiGe/Si quantum wells for piezoresistive applications

Reparaz

Goñi

Alonso

et al. 2013

Physica Status Solidi (b)

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In this work, we have theoretically investigated the influence of quantum confinement, biaxial stress, and high hydrostatic pressure on the valence band structure of Si 1Àx Ge x /Si quantum wells (QW) with x ranging from 0.1 to 0.75, QW thicknesses up to 50 nm, and hydrostatic pressures up to 8 GPa. Using the Nextnano simulator, we have solved the 6 Â 6 k Á p Hamiltonian obtaining the valence band eigenvalues (for light-and heavyhole states) as well as their dispersion close to k ¼ 0. We have found that for specific combinations of x, QW thickness, and hydrostatic pressure, it is possible to tailor the energy of the light-and heavy-hole states in such a way that they become almost degenerate for k ¼ 0.This results in a larger interaction between these sub-bands leading to an electron-like dispersion of certain hole sub-bands. We present representative examples showing that as pressure increases from 0 to 4 GPa the dispersion type of the hole states progressively evolves from electron-like to almost hole-like, which naturally produces sharp peaks in their corresponding density of states at k 6 ¼ 0. The opposite transition from hole-like to electron-like band dispersion is also briefly discussed. This peculiar behavior of the dispersion type of the valence subbands induced by hydrostatic pressure results particularly interesting for piezoresistive applications, since large changes in the electrical conductivity are expected as a function of external stress.

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“…The phonons involved in inter-valley scattering, their wave-vectors, EPC matrix elements that generate them TABLE I. List of the phonons generated by EPC, their calculated EPC scattering matrix element 18,[22][23][24] and phononphonon anharmonic decay times. Phonons are in reduced coordinates.…”

Section: A Electron-phonon Scatteringmentioning

confidence: 99%

Evolution of non-thermal phonon and electron populations in photo-excited germanium on picosecond timescales

Murphy-Armando,

Murray,

Savić

et al. 2019

Preprint

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We investigate the generation of phonons on picosecond timescales and the relaxation of carriers in multiple conduction band valleys of photo-excited Ge by intervalley electron-phonon scattering. Simulations of the time-evolution of phonon populations, based on first-principles band structure and electron-phonon and phonon-phonon matrix elements, are compared with data from timeresolved x-ray diffuse scattering experiments, performed at the LCLS free-electron laser facility, which measures the diffuse scattering intensity following photo-excitation by a 50 fs near-infrared optical pulse. Non-thermal phonon populations throughout the Brillouin zone are observed and simulated for times up to 10 ps. Comparing calculations and measurements show that the intensity of non-thermal x-ray diffuse scattering signal, that is observed to grow substantially near the L-point of the Brillouin zone over 3-5 ps, is due to phonons generated by scattering of carriers between the ∆ and L valleys. With inclusion of phonon decay through 3-phonon processes, the simulations also account for other non-thermal features observed in the x-ray diffuse scattering intensity, which are due to anharmonic phonon-phonon scattering of the phonons initially generated by electron-phonon scattering.

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Giant piezoresistance in silicon-germanium alloys

Cited by 12 publications

References 28 publications

Enhancement of the electronic thermoelectric properties of bulk strained silicon-germanium alloys using the scattering relaxation times from first-principles calculations

Enhancement of the electronic thermoelectric properties of bulk strained silicon-germanium alloys using the scattering relaxation times from first-principles calculations

Valence band structure engineering of thin SiGe/Si quantum wells for piezoresistive applications

Evolution of non-thermal phonon and electron populations in photo-excited germanium on picosecond timescales

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