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Frequency Resolved Phonon Transport in Si/Ge Nanocomposites

[+] Author Affiliations
Dhruv Singh, Jayathi Y. Murthy, Timothy S. Fisher

Purdue University, West Lafayette, IN

Paper No. IPACK2011-52244, pp. 757-768; 12 pages
doi:10.1115/IPACK2011-52244
From:
  • ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems
  • ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, MEMS and NEMS: Volume 1
  • Portland, Oregon, USA, July 6–8, 2011
  • ISBN: 978-0-7918-4461-8
  • Copyright © 2011 by ASME

abstract

In this paper, we analyze cross plane phonon transport and thermal conductivity in two-dimensional Si/Ge nanocomposites. A non-gray BTE model that includes full details of phonon dispersion, the spread in phonon mean free paths and the frequency dependent transmissivity is used to simulate thermal transport. The general conclusions inferred from gray BTE simulations that the thermal conductivity of the nanocomposite is much lower than its constituent materials and interfacial density as the parameter determining thermal conductivity remain the same. However, it is found that the gray BTE significantly overpredicts thermal conductivity in the length scales of interest and quantitatively reliable results are obtained only upon inclusion of the details of phonon dispersion. The transition of phonon transport from ballistic regime to near diffusive regime is observed by looking at a large range of length scales. Non-equilibrium energy exchange between optical and acoustic phonons and the granularity in phonon mean free paths are found to significantly affect thermal conductivity leading to departures from the frequently employed gray approximation. It is also found that the frequency content of thermal conductivity in the nanocomposite extends out to a much larger frequency range unlike bulk Si and Ge. Scattering against heterogeneous interfaces is very effective in suppressing thermal conductivity contribution from the low frequency acoustic phonons but less so for high frequency phonons, which have much smaller mean free paths.

Copyright © 2011 by ASME

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