Experimental determination of the thermoelectric properties of porous silicon nanowires

"The thermoelectric properties of nanostructured silicon have attracted significant attention in recent work. The objective is to reduce thermal conductivity through the introduction of phonon scattering mechanisms while preserving charge transport. Initial reports on electrolessly etched silicon nanowires and periodic \holey"" silicon membranes contained several puzzling aspects that remain unresolved. Here, we present measurements on mesoporous silicon nanowires fabricated through electroless etching of degenerately doped silicon. While thermal conductivity in this material at room temperature is attractive for thermoelectric applications at ~2 W/(m K), charge transport is severely degraded due to the disordered yet nanocrystalline structure. We investigate post doping conditions to improve the electrical conductivity by ~3 orders of magnitude. TEM characterization confirmed that porosity and crystalline structure are retained after doping. We characterized the boron concentration before and after doping by secondary ion mass spectroscopy (SIMS). Raman spectroscopy was also employed to extract the free carrier concentrations as well as nanocrystalline size. We measured the Seebeck coefficient and thermal conductivity from 30 K to 400 K by a frequency domain technique. Analysis of Seebeck coefficient reveals the electron scattering mechanism in porous silicon nanowire before and after post-doping. The carrier concentrations extracted from Seebeck coefficient are in good agreement with the Raman spectrum analysis. In order to interpret the thermal conductivity data, we propose a frequency dependent multiple scattering of phonons across the porous wire. This work provides detailed insight into charge and heat transport in disordered yet nanocrystalline materials and advances their engineering for thermoelectric waste heat harvesting amongst other applications."

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Tian, Hongxiang

Contributors dc:contributor

• Sinha, Sanjiv
• Li, Xiuling
• Ertekin, Elif
• Toussaint, Kimani

• thermoelectric
• porous silicon nanowire
• phonon transport in porous silicon nanowire
• electron transport

Statement dc:rights

• Copyright 2014 Hongxiang Tian

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/73006

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/73006