Thermal conductivity of Si–Ge superlattices

Lee, S.-M.; Cahill, David G.; Venkatasubramanian, R.

doi:10.1063/1.118755

Cited by 682 publications

(597 citation statements)

References 16 publications

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“…According to experimental [5,6] and modeling [9,19,21] results on Si/Ge superlattices, anharmonic effects are not important for temperatures below 500 K. The anharmonicity would become important when the phonon mean free path due to anharmonicity becomes smaller than the superlattice length L. In the harmonic regime, specular scattering leads to coherent wave effects [29][30][31], while diffuse scattering could destroy coherence.…”

Section: Methodsmentioning

confidence: 99%

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Green's function studies of phonon transport across Si/Ge superlattices

2014

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Understanding and manipulating coherent phonon transport in solids is of interest both for enhancing the fundamental understanding of thermal transport as well as for many practical applications, including thermoelectrics. In this study, we investigate phonon transmission across Si/Ge superlattices using the Green's function method with first-principles force constants derived from ab initio density functional theory. By keeping the period thickness fixed while changing the number of periods, we show that interface roughness partially destroys coherent phonon transport, especially at high temperatures. The competition between the low-frequency coherent modes and high-frequency incoherent modes leads to an optimum period length for minimum thermal conductivity. To destroy coherence of the low-frequency modes, scattering length scale on the order of period length is required. This finding is useful to guide the design of superlattices to reach even lower thermal conductivity.

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Section: Methodsmentioning

confidence: 99%

“…The thermal conductivity of superlattices can be even lower than their alloy counterparts [5][6][7][8]. Although diffuse scattering at interfaces is responsible for the remarkable thermal conductivity reduction [9,10], coherent phonon transport has been experimentally observed in GaAs/AlAs superlattices [11] and perovskite oxides [12].…”

Section: Introductionmentioning

confidence: 99%

Green's function studies of phonon transport across Si/Ge superlattices

2014

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“…However, we can extract the values from superlattices by assuming that the measured thermal resistance of superlattices 50 can be regarded as reasonable agreement since our calculations are on interfaces formed from two perfect bulk materials and should be compared with larger period thickness. The larger experimental results of interface thermal conductance with small period thickness could be attributed to the coherent phonon transport in the superlattice and deserves further studies.…”

Section: Interface Thermal Conductance Of Si/ge Interfacementioning

confidence: 99%

“…52 Si/Ge Superlattices are expitaxially grown at relatively high temperature, i.e., about 1000 K in Ref. 50, which can induce atomic reconstruction in the lattice-mismatched Si/Ge interfaces.…”

Section: Interface Thermal Conductance Of Si/ge Interfacementioning

confidence: 99%

Effect of lattice mismatch on phonon transmission and interface thermal conductance across dissimilar material interfaces

Yang

2012

Phys. Rev. B

131

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When phonons transport across a material interface, they experience reflection, transmission and mode conversion, which results in a local temperature jump at interface and thus dramatically changes the thermal conductivity of nanostructured materials. Phonon transmission across lattice-matched interfaces has been studied extensively in recent years with the atomistic Green's function (AGF) approach, which usually uses one unit cell to represent the cross-section along the interface. However, modeling phonon transmission across realistic material interfaces is much more challenging because realistic interfaces are usually latticemismatched ones with atomic reconstruction, defects, and species mixing, which demands a larger cross-sectional area for the AGF simulation. In this paper, an integrated molecular dynamics (MD) and AGF approach is developed to study the phonon transmission across latticemismatched interfaces. MD simulation is used to simulate atomic reconstruction close to the 1 Email: Ronggui.Yang@Colorado.Edu interface. The recursive AGF approach is then employed for the first time to calculate frequencydependent phonon transmission across lattice-mismatched interfaces with defects and species mixing, which addresses the numerical challenge in calculating phonon transmission for a relatively large cross-sectional area with reduced computational cost. The study of the relaxed interface formed from two semi-infinite bulk materials shows that lattice mismatch increases the lattice disorder and decreases the adhesion energy, which in turn lowers phonon transmission and reduces the interface thermal conductance across lattice-mismatched interfaces. Low-frequency phonons can be significantly scattered by increasing the defect size across the interface while high frequency phonons can be scattered almost completely (phonon transmission <0.1) across an alloyed layer as thin as 2.27 nm. The effect of lattice-mismatch on phonon transmission becomes smaller for interfaces with defects and species mixing. The effect of annealing temperature on the Si/Ge interface thermal conductance was studied. A significant reduction of the Si/Ge interface thermal conductance was observed for a lattice-mismatched interface when annealed at high temperature, which agrees well with the available experimental data in literature.

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“…As shown in Fig.2(c), the Dirac cones from the graphene layer and the interface between BI and TI contribute to the multiple charge conducting channels around the Fermi level. Moreover, a possible defect formation in PbBi 2 Se 4 may lead to a decrease of thermal conductivity 26 , while the topologically protected interfacial Dirac cones are robust with respect to the non-magnetic defect; this situation resembles the phonon-blocking and electron-transmitting strategy 27 .…”

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confidence: 99%