Isotope doping-induced crossover shift in the thermal conductivity of thin silicon nanowires

Abstract

Here, using homogeneous nonequilibrium molecular dynamics (HNEMD) simulations, we report the thermal transport characteristics of thin Si nanowires (NWs) with varying size and isotope doping ratio. It is identified that crossover in the thermal conductivity (κ) of both isotope doping-free and isotope doped Si-NWs appears at critical sizes, below which κ is enlarged with decreasing size because the hydrodynamic phonon flow predominates, above which, due to the dominant phonon boundary scattering, opposite behavior is observed. With increasing isotope doping, however, the critical size in minimizing the κ is moved to small values because the phonon impurity scattering caused by isotope doping is critically involved. Moreover, there is a critical isotope doping (< 50%) in the critical size motion, originating from that, above which, the critical size no longer moves due to the persistence of hydrodynamic phonon flow. This study provides new insights into the thermal transport behaviors of quasi-1D structures.

Thermal conductivity of fivefold twinned silicon-germanium heteronanowires

“…19 Previous studies uncovered that this “flipped” behavior in κ of extremely thin NWs can be attributed to the hydrodynamic phonon flow due to the normal (N) three-phonon scattering process in the low-frequency region. 18–20…”

“…To gain a deeper physical understanding of the anomalous heat transport behavior in 5FT-NWs, three-phonon scattering rates are calculated. As is known, when heat is transported in extremely thin NWs composed of Si, 18,20 GaP 68 and C, 19 the dominant process for heat transport is the N-process, resulting in a hydrodynamic phonon “fluid” flow. This N-process leads to an increase in κ , while the weaker U-process also exists.…”

“…Very recently, it was revealed that as a result of phonon hydrodynamic flow formed in the Si-NWs, extremely thin NWs show abnormally high κ . 17–20 Compared with layered materials, 21–24 however, κ of Si-NWs remains relatively high. A further reduction in the κ of Si-NWs is necessary to achieve enhanced performance of thermoelectric conversion.…”

“…A further reduction in the κ of Si-NWs is necessary to achieve enhanced performance of thermoelectric conversion. 20,25–29…”

“…This is attributed to the fact that Si-NWs are able to conduct charges well but show weak ability in heat transport, in contrast to bulk Si. Very recently, it was revealed that as a result of phonon hydrodynamic flow formed in the Si-NWs, extremely thin NWs show abnormally high k. [17][18][19][20] Compared with layered materials, [21][22][23][24] however, k of Si-NWs remains relatively high. A further reduction in the k of Si-NWs is necessary to achieve enhanced performance of thermoelectric conversion.…”