From Amorphous to Nanocrystalline: The Effect of Nanograins in an Amorphous Matrix on the Thermal Conductivity of Hot-Wire Chemical-Vapor Deposited Silicon Films

William Nemeth, B. Kearney, B. Jugdersuren, D. Queen, Thomas Metcalf, J. Culbertson, P. Desario, R. Stroud, Q. Wang, Xiao Liu

Research output: Contribution to journalArticlepeer-review

13 Scopus Citations

Abstract

We have measured the thermal conductivity of amorphous and nanocrystalline silicon films with varying crystalline content from 85 K to room temperature. The films were prepared by the hot-wire chemical-vapor deposition, where the crystalline volume fraction is determined by the hydrogen (H2) dilution ratio to the processing silane gas (SiH4), R = H2/SiH4. We varied R from 1 to 10, where the films transform from amorphous for R < 3 to mostly nanocrystalline for larger R. Structural analyses show that the nanograins, averaging from 2 to 9 nm in sizes with increasing R, are dispersed in the amorphous matrix. The crystalline volume fraction increases from 0 to 65% as R increases from 1 to 10. The thermal conductivities of the two amorphous silicon films are similar and consistent with the most previous reports with thicknesses no larger than a few μm deposited by a variety of techniques. The thermal conductivities of the three nanocrystalline silicon films are also similar, but are about 50-70% higher than those of their amorphous counterparts. The heat conduction in nanocrystalline silicon films can be understood as the combined contribution in both amorphous and nanocrystalline phases, where increased conduction through improved nanocrystalline percolation path outweighs increased interface scattering between silicon nanocrystals and the amorphous matrix.

Original languageAmerican English
Article number085301
Number of pages8
JournalJournal of Physics Condensed Matter
Volume30
Issue number8
DOIs
StatePublished - 29 Jan 2018

Bibliographical note

Publisher Copyright:
© 2018 IOP Publishing Ltd.

NREL Publication Number

  • NREL/JA-5J00-70759

Keywords

  • amorphous silicon
  • chemical vapor deposition
  • nanocrystalline silicon
  • nanoscale phonon scattering
  • thermal conductivity

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