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Research Papers: Micro/Nanoscale Heat Transfer

Molecular Dynamics Simulation of Phonon Scattering at Silicon/Germanium Interfaces

[+] Author and Article Information
Lin Sun

Rosen Center for Advanced Computing, Purdue University, West Lafayette, IN 47906sun33@purdue.edu

Jayathi Y. Murthy

School of Mechanical Engineering, Purdue University, West Lafayette, IN 47906jmurthy@purdue.edu

J. Heat Transfer 132(10), 102403 (Jul 27, 2010) (9 pages) doi:10.1115/1.4001912 History: Received June 02, 2009; Revised April 16, 2010; Published July 27, 2010; Online July 27, 2010

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.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) Simulation domain with two materials, A and B, and a rough interface inserted in between. A phonon wave is created at the center of material A and propagates to B by crossing interfaces. (b) A regularly patterned roughness structure at the interface, shown in cross-section. The white and gray squares refer to materials A and B, respectively.

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Figure 2

Illustration of an LA wave packet example centered at k0=0.1(2π/a) and z=400a

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Figure 3

Dispersion relation for materials A (silicon) and B (germanium) in the [001] direction

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Figure 4

Snapshots of displacement (respectively at 10 ps, 17 ps, and 25 ps) for an LA wave packet with frequency 1.34 THz

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Figure 5

Distribution of reflected and transmitted phonons in k space

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Figure 6

Energy change with time for material A and B for the case that incident LA phonons are at k=0.5(2π/a)

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Figure 7

Phonon transmissivity for LA wave packets at smooth Si/Ge interface

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Figure 8

Random roughness illustration: atoms at interface are endowed with mass randomly (illustrated by colors) to represent the ROUGHNESS

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Figure 9

Regularly patterned roughness: two materials, A and B are mixed in a regular pattern. The dimension of each unit is indicated by h, l, and d. This pattern is extruded in z-direction up to a prescribed thickness with successive layers being staggered with respect to each other.

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Figure 10

Phonon transmissivity for an interface with regularly patterned roughness

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Figure 11

Energy change with time for materials A and B and the interface region for LA phonon transport across a regularly patterned interface for k/(2π/a)=0.5 and thickness of 10a. Incident energy is normalized to unity.

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Figure 12

Snapshots of phonon propagation at the interface with regularly patterned roughness for k/(2π/a)=0.5 and thickness=10a

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Figure 13

Evolution of phonon distribution in k space with time in interface region

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Figure 14

Phonon distribution in k space for reflected phonon in material A and transmitted phonon in material B after interface interaction at 25 ps

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