Reduced Thermal Conductivity in Nanoengineered Rough Ge and GaAs Nanowires

Abstract

We model and compare the thermal conductivity of rough semiconductor nanowires (NWs) of Si, Ge, and GaAs for thermoelectric devices. On the basis of full phonon dispersion relations, the effect of NW surface roughness on thermal conductivity is derived from perturbation theory and appears as an efficient way to scatter phonons in Si, Ge, and GaAs NWs with diameter D < 200 nm. For small diameters and large root-mean-square roughness Delta, thermal conductivity is limited by surface asperities and varies quadratically as (D/Delta)(2). At room temperature, our model previously agreed with experimental observations of thermal conductivity down to 2 W m(-1) K(-1) in rough 56 nm Si NWs with Delta = 3 nm. In comparison to Si, we predict here remarkably low thermal conductivity in Ge and GaAs NWs of 0.1 and 0.4 W m(-1) K(-1), respectively, at similar roughness and diameter.

Thermal conductivity of GaAs nanowires studied by micro-Raman spectroscopy combined with laser heating

“…The conductivity is found to be significantly lower in NWs than in bulk GaAs. Furthermore, our results confirm recent theoretical calculations by Martin et al [7].…”

“…The conductivity is found to be significantly lower in NWs than in bulk GaAs. Furthermore, our results confirm recent theoretical calculations by Martin et al [7].We use zincblende NWs grown by gallium-assisted molecular beam epitaxy, exhibiting very high structural quality [8] and diameters d between 150 and 170 nm. The facets belong to the {110} family and the NW axis corresponds to the [111] direction.…”

“…This might also be due to the oxidation and the formation of amorphous arsenic by laser induced heating, since the modes associated to the formation of arsenic as well as oxide can be observed for higher power conditions [19]. Recently, theoretical calculations of κ for GaAs NWs have been published by Martin et al [7]. For smooth GaAs NWs with d between 100 and 200 nm and temperatures between 300 and 400 K they report values of κ between 11 and 20 Wm −1 K −1 .…”

Polar surface effects on the thermal conductivity of ZnO nanowires: a shell-like surface reconstruction-induced preserving mechanism

“…24,25,26,27,28 The thermoelectric phenomenon can be utilized to harvest otherwise wasted thermal energy directly into electric power. To increase the thermoelectric efficiency, the thermal conductivity in NWs should be reduced, which can be realized through phonon confinement effects, 29,30,31,32 isotope doping, 33 surface roughness, 34,35,36 or non-planar (kinked) structures. 37 Shi et al suggested enhancing the thermoelectric efficiency through gallium doping, and the thermoelectric figure of merit was found to be increased by a factor of 2.5 at 4% gallium doping.…”

A study of the impact of dislocations on the thermoelectric properties of quantum wells in the Si/SiGe materials system

“…6 Although, some/many aspects of the thermal and electrical transport maybe considered to be independent of the exact fabrication process implemented, two important scattering mechanisms which can depend on the exact nature of the quality of the epitaxial growth are interface roughness and dislocation scattering, these two mechanisms are related to some degree. 7,8 roughness scattering on thermal conductivity has been studied previously, 9,10 although little has been done in the context of thermoelectrics directly where it is important to consider both electrical and thermal transport. However, for strain-balanced multiple quantum well superlattices, the formation of a number of threading edge dislocations is inevitable and dislocations are likely to play a dominant role, in determining the feasibility of such structures.…”