The theoretical laser-flash method is used to calculate the thermal conductivity of the ${\text{Si}}_{200}{X}_{32}$ ($X=\text{H}$, D, or OH) and ${\text{Si}}_{296}{X}_{112}$ ($X=\text{H}$ or D) nanowires. The main emphasis is on the role of defects, which are described using first-principles methods. The defects considered are the surface of the nanowire, random distributions of substitutional C or Ge impurities, and monoatomic $\delta$ layers of C or Ge. The localized vibrational modes of these defects are explicitly included in the calculations and no empirical defect-related parameter is introduced. We find that the surface Si–H wag modes couple resonantly to each other much faster than they decay into bulk modes, which leads to distinct surface and bulk contributions to the thermal conductivity. The spatially-localized vibrational modes associated with the Ge or C impurities as well as the $\delta$ layers trap thermal phonons thus reducing the thermal conductivity.

• Received 11 December 2013
• Revised 24 January 2014

DOI:https://doi.org/10.1103/PhysRevB.89.155409