Theory of interface scattering of phonons in superlattices

Abstract

We present an atomic-scale theory of interface scattering of phonons in superlattices. In particular, we describe the scattering as a result of two features, mixing of atoms at interfaces and presence of dislocations at interfaces due to lattice mismatch. We apply the theory to quantitatively explain the thermal conductivity, and its variation with period and temperature, of Si/Ge superlattices.

Atomistic modeling of anharmonic phonon-phonon scattering in nanowires

“…7(a) are considered. Such devices, if the Si-Ge periods are repeated as in superlattices, could exhibit very low thermal conductivities 20,49 while keeping relatively good electronic properties, thus fulfilling two important criteria needed for high performance thermogenerators. Since the maximum phonon energy in Ge is smaller than in Si (37 vs. 64 meV with the harmonic parameters of Ref.…”

“…Measurement techniques have evolved to the point where they can provide a deep insight into the thermal conduction of nanowires 10,11 , which is essential for both electronic and thermoelectric applications. A the same time the theoretical understanding of the thermal properties of nanowires has kept improving due to the development of always complexer and more accurate models [12][13][14][15][16][17][18][19][20][21][22][23] . In many cases, a direct comparison of experimental data and simulation results is possible.…”

“…In spite of the computational complexity, ultra-scaled nanowires with a diameter of 3 nm, different crystal orientations (<100>, <110>, and <111>), lengths (20,40, and 60 nm), temperatures (from 50 to 1000 K), and made of more than 20000 atoms can be simulated within a couple of hours. As applications, the thermal current flowing through such nanowires as well as the resulting thermal resistance and conductivity are calculated.…”

“…However, at the nanometer scale, such approaches are no more valid and must be replaced by models treating thermal transport at the phonon level. Nowadays, most theoretical investigations of nanoscale thermal transport are based either (i) on the linearized Boltzmann Transport Equation with Fermi's Golden Rule 15,16,20,21 , (phonon quantum confinement neglected) (ii) on Equilibrium Molecular Dynamics simulations 23 (computationally very intensive and statistical average over long time periods required), (iii) on first-principle (ab-initio) methods 19 (limited to very small systems), or (iv) on coherent phonon Non-equilibrium Green's Function (NEGF) approaches 12,17,22 (no dissipative interactions). The versatility and flexibility of NEGF 25,26 make it one of the most widely-spread and appreciated formalisms to solve quantum transport problems.…”

Interfacial electron and phonon scattering processes in high-powered nanoscale applications.

“…We discuss the veracity of this assumption later. Previous works have modeled phonon transport across heterointerfaces incorporating non-idealities such as extended chemical intermixing, 21,22,24 misfit dislocations, 19,81 and microcrystalline or amorphous regions. 21,22,25,82 In all of these previous works, changes in h K were controlled by changes in the diffusive phonon scattering events around the interface caused by these non-idealities.…”