Lattice thermal conduction in ultra-thin nanocomposites
Journal of Applied Physics
Reason for embargo
We have studied the lattice thermal conductivity of Si/Ge periodic nanocomposites (superlattice, nanowire, and nanodot structures) of sample sizes in the range of 30 nm-30 μm, periodicities 1.1 nm and 2.2 nm, with reasonably dirty interfaces, and n-type doping concentration in the range of 1023-1026m-3. Our calculations employ a judicious combination of ab initio and physically sound semi-empirical methods for detailed calculations of estimates of phonon scattering rates due to anharmonicity and interface formation. Based upon our results we conclude that the formation of ultra-thin nanocomposites in any of the three structures is capable of reducing the conductivity below the alloy limit. This can be explained as a result of combination of the sample length dependence, the on-set of mini-Umklapp three-phonon processes, mass mixing at the interfaces between Si and Ge regions, and the sample doping level.
We are grateful to the EPSRC (UK) for supporting this project via the Grant Award No.r EP/H046690/1. Quantum Espresso calculations were performed on the Intel Nehalem (i7) cluster (ceres) at the University of Exeter. I.O.T. also acknowledges support from the John Templeton Foundation as part of the Durham Emergence Project during the final stages of this work.
This is the final version of the article. Available from the publisher via the DOI in this record.
Vol. 119, 244309 (2016)