TY - JOUR
T1 - From Amorphous to Nanocrystalline: The Effect of Nanograins in an Amorphous Matrix on the Thermal Conductivity of Hot-Wire Chemical-Vapor Deposited Silicon Films
AU - Nemeth, William
AU - Kearney, B.
AU - Jugdersuren, B.
AU - Queen, D.
AU - Metcalf, Thomas
AU - Culbertson, J.
AU - Desario, P.
AU - Stroud, R.
AU - Wang, Q.
AU - Liu, Xiao
N1 - Publisher Copyright:
© 2018 IOP Publishing Ltd.
PY - 2018/1/29
Y1 - 2018/1/29
N2 - 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.
AB - 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.
KW - amorphous silicon
KW - chemical vapor deposition
KW - nanocrystalline silicon
KW - nanoscale phonon scattering
KW - thermal conductivity
UR - http://www.scopus.com/inward/record.url?scp=85041910528&partnerID=8YFLogxK
U2 - 10.1088/1361-648X/aaa43f
DO - 10.1088/1361-648X/aaa43f
M3 - Article
C2 - 29283107
AN - SCOPUS:85041910528
SN - 0953-8984
VL - 30
JO - Journal of Physics Condensed Matter
JF - Journal of Physics Condensed Matter
IS - 8
M1 - 085301
ER -