Molecular Dynamics Simulation of Phonon Scattering at Silicon/Germanium Interfaces

Abstract

Detailed phonon transport at Si/Ge interfaces is studied using the molecular dynamics wave-packet method. Three types of interfaces are investigated: A smooth interface, an interface with random roughness, and an interface with a regularly patterned roughness. The phonon transmissivity for each case is calculated as a function of phonon frequency, roughness characteristic length, and atomic structure. For a smooth interface, the transmissivities predicted by the MD simulations agree well with the acoustic mismatch model based on the continuum assumption. The rough interface simulation results indicate that random roughness is the source of incoherent phonon scattering and decreases the phonon transmission. Periodic structures such as the regularly patterned roughness employed in this paper cause strong phonon wave interference and may restore phonon transmission as the layer thickness increases.

Thermal boundary conductance across rough interfaces probed by molecular dynamics

“…The case of atomic roughness has been more widely addressed in the literature, and wave-packet simulations 36 give a clear picture of the effect of small atomic roughness on phonon transmission: long wavelength phonons see the interface as ideal and do not contribute to the change of the thermal boundary conductance. On the other hand, short wavelength phonons strongly interact with the small scale roughness, and the corresponding change in phonon transmission is found to depend on the structure of the interface: for regular shaped patterned interfaces, constructive wave interference lead to enhanced transmission thereby increasing the boundary conductance 37 .…”

Nonequilibrium phonon mean free paths in anharmonic chains

“…This expression can be shown to be equivalent to the classical Boltzmann-Peierls expression [35] for thermal conductivity, allowing us to interpret (ω) as the "transport relaxation length" [36]. In low-dimensional materials, where the relaxation time approximation is often inadequate [27], calculating the transport relaxation length from quantum-mechanical first-principles calculations generally requires the full solution of the Boltzmann equation [37].…”

Boundary scattering of phonons: Specularity of a randomly rough surface in the small-perturbation limit

“…Many of these studies involve detailed models of a rough surface or interface at the atomic level and use either lattice dynamics calculations based on Green's functions analysis [25][26][27][28][29] or molecular dynamics simulations [32][33][34][35]. These advanced studies heavily rely on numerical computations; hence it is difficult to generalize their results beyond specific systems considered in each particular paper.…”

“…In recent years, a number of advanced and sophisticated models of boundary scattering have been applied to the analysis of thermal transport in nanostructures [25][26][27][28][29][30][31][32][33][34][35]. Many of these studies involve detailed models of a rough surface or interface at the atomic level and use either lattice dynamics calculations based on Green's functions analysis [25][26][27][28][29] or molecular dynamics simulations [32][33][34][35].…”