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Title: Significant thermal conductivity reduction of silicon nanowire forests through discrete surface doping of germanium

Silicon nanowires (SiNWs) are promising materials for the realization of highly-efficient and cost effective thermoelectric devices. Reduction of the thermal conductivity of such materials is a necessary and viable pathway to achieve sufficiently high thermoelectric efficiencies, which are inversely proportional to the thermal conductivity. In this article, vertically aligned forests of SiNW and germanium (Ge)-doped SiNW with diameters around 100 nm have been fabricated, and their thermal conductivity has been measured. The results show that discrete surface doping of Ge on SiNW arrays can lead to 23% reduction in thermal conductivity at room temperature compared to uncoated SiNWs. Such reduction can be further enhanced to 44% following a thermal annealing step. By analyzing the binding energy changes of Ge-3d and Si-2p using X-ray photoelectron spectroscopy, we demonstrate that surface doped Ge interacts strongly with Si, enhancing phonon scattering at the Si-Ge interface as has also been shown in non-equilibrium molecular dynamics studies of single nanowires. Overall, our results suggest a viable pathway to improve the energy conversion efficiency of nanowire-forest thermoelectric nanomaterials.
Authors:
; ; ; ;  [1] ;  [2]
  1. Laboratory of Thermodynamics in Emerging Technologies, Department of Mechanical and Process Engineering, ETH Zurich, Sonneggstrasse 3, 8092 Zurich (Switzerland)
  2. Department of Mechanical Engineering, University College London, London, WC1E 7JE (United Kingdom)
Publication Date:
OSTI Identifier:
22412767
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 106; Journal Issue: 9; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 77 NANOSCIENCE AND NANOTECHNOLOGY; ANNEALING; BINDING ENERGY; COMPARATIVE EVALUATIONS; DOPED MATERIALS; ENERGY CONVERSION; GERMANIUM; INTERFACES; MOLECULAR DYNAMICS METHOD; NANOMATERIALS; NANOWIRES; PHONONS; SILICON; SURFACES; TEMPERATURE RANGE 0273-0400 K; THERMAL CONDUCTIVITY; X-RAY PHOTOELECTRON SPECTROSCOPY