Effects of vacancy defects location on thermal conductivity of silicon nanowire: a molecular dynamics study

Abstract

The improvement of thermoelectric figure of merit of silicon nanowire (SiNW) can be achieved by lowering its thermal conductivity. In this work, non-equilibrium molecular dynamics method was used to demonstrate that the thermal conductivity of bulk silicon crystal is drastically reduced when it is crafted as SiNW and that it can be reduced remarkably by including vacancy defects. It has been found that 'centre vacancy defect' contributes much more in reducing the thermal conductance than 'surface vacancy defect'. The lowest thermal conductivity that occurs is about 52.1% of that of pristine SiNW, when 2% vacancy defect is introduced in the nanowire. The vibrational density of states analysis was performed to understand the nature of this reduction and it has been found that the various boundary scatterings of phonon significantly reduce the thermal conductivity. Also, larger mass difference due to voids induces smaller thermal conductivity values. These results indicate that the inclusion of vacancy defects can enhance the thermoelectric performance of SiNWs.

Effects of vacancies on the thermal conductivity of Si nanowires

“…As none of these potentials was specifically parameterized to account for the vibrational or heat transport properties of Si, it is difficult to tell which of these results is more reliable (though the linear dependence seems to contradict the results obtained with analogous calculations in bulk Si 23,24 ). Similar calculations were carried out by Meem et al 30 The separation between thermostats is in this case even shorter, amounting to only ∼7 nm. Furthermore, they considered a very unusual and unrealistic distribution of vacancies, obtained by removing Si atoms along a line parallel to the wire axis.…”

“…Similar conclusions were reached by the one-dimensional distribution of vacancies considered in ref. 30.…”