Nanoscale Physics

Thermal conductivity of Si/Ge and Ge/Si core–shell nanowires: molecular dynamics study
Semchuk S.S.1, Kuryliuk V.V.1
1 Department of Physics, Taras Shevchenko National University of Kyiv.      64/13 Volodymyrska str., Kyiv 01601, Ukraine. 
E-mail: cavej85@gmail.com

Understanding and predicting the thermal conduction in the semiconductor nanowire are crucial for designing the thermoelectric devices [1]. Recent experiments on silicon nanowires have shown them to be promising thermoelectric structures, because of the reduction in thermal conductivity from increased phonon scattering by the surface [2]. Numerous techniques have been proposed to further reduce the thermal conductivity of Si nanowires, involving doping, surface modification or nanopores introducing. 
In this study, we report on the effect of Ge/Si (Si/Ge) core-shell content on thermal conductivity of nanowires at various temperatures. Non-equilibrium molecular dynamics simulation is performed to investigate thermal conductivities of two kinds of SiGe nanowires (core(Si)/shell(Ge) and core(Ge)/(Si)) with rectangular cross-sectional geometry. By analyzing the phonon density of states and phonon relaxation times, it is revealed that the large reduction in the thermal conductivity of Si/Ge and Ge/Si core-shell nanowires stems from the strong localization of the phonon modes due to interface scattering. We show that the thermal conductivity variation with temperature in core-shell nanowires is much weaker than in pure Si or Ge nanowires. 

1.	Amato M., Palummo M., Rurali R., Ossicini S. Silicon−Germanium Nanowires: Chemistry and Physics in Play, from Basic Principles to Advanced Applications // Chem. Rev. – 2014. – 114. – P.1371-1412.
2.	Hochbaum A. I.; Chen R.; Delgado R. D.; Liang W.; Garnett E. C.; Najarian M.; Majumdar A.; Yang P. Enhanced thermoelectric performance of rough silicon nanowires // Nature. – 2008. – 451. – P. 163-167.