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Epitaxial Growth and Design of Nanowires and Complex Nanostructures

Dick Thelander, Kimberly LU (2007)
Abstract (Swedish)
Popular Abstract in Swedish

Denna avhandling behandlar epitaxiell växt av nanotrådar i III-V halvledarmaterial, i vilken guldpartiklar använts som frö, samt design av tredimensionella mer avancerade förgrenade strukturer baserade på dessa trådar. Växten utfördes via så kallad ?MetallOrganic Vapour Phase Epitaxy? (MOVPE), i vilken prekursormolekylerna till halvledarmaterialens komponenter tillförs i form av ånga vid lågt tryck. Nanotrådar växer epitaxiellt med kontrollerad kristallorientering från halvledarsubstrat; kontrollerad diameter uppnås via guldpartiklarnas storlek medan längden kontrolleras av växtparametrarna.



Partikel-assisterad nanotrådsväxt används i stor omfattning idag för att uppnå... (More)
Popular Abstract in Swedish

Denna avhandling behandlar epitaxiell växt av nanotrådar i III-V halvledarmaterial, i vilken guldpartiklar använts som frö, samt design av tredimensionella mer avancerade förgrenade strukturer baserade på dessa trådar. Växten utfördes via så kallad ?MetallOrganic Vapour Phase Epitaxy? (MOVPE), i vilken prekursormolekylerna till halvledarmaterialens komponenter tillförs i form av ånga vid lågt tryck. Nanotrådar växer epitaxiellt med kontrollerad kristallorientering från halvledarsubstrat; kontrollerad diameter uppnås via guldpartiklarnas storlek medan längden kontrolleras av växtparametrarna.



Partikel-assisterad nanotrådsväxt används i stor omfattning idag för att uppnå välkontrollerade strukturer. Den rådande förståelsen av denna växtmekanism utvecklades för över fyrtio år sedan, och går under benämningen ?Vapour-Liquid-Solid ? (VLS). Denna modell indikerar formationen av en flytande legering mellan partikeln och växtmaterialet/växtmaterialen, samt fortskridande växt genom utfällning från en övermättad partikel. Den förhöjda växttakten för nanotrådar, i förhållande till bulkväxt direkt från ånga, tillskrivs vanligen en fördelaktig sönderdelning utav prekursor molekylerna vid eller nära partikelns yta.



Till denna modell, vilken var utvecklad för guldpartikel-assisterad växt av kiseltrådar, har nyligen motsägelsefulla observationer gjorts i partikel-assisterad växt i andra material. Utmärkande är framförallt rapporter om nanotrådsväxt vid temperaturer som är för låga för att en flytande legering ska uppstå. Vidare så har också nanotrådväxt rapporterats för system där prekursormolekyler inte används, därvid kan ej den förhöjda växttakten förklaras via en fördelaktig sönderdelning. Andra rapporter har visat att sådan sönderdelning inte nödvändigtvis förekommer när prekursormolekyler används. Den första delen av denna avhandling presenterar den förståelse av partikel-assisterad växt som finns i dag, både generellt och för de specifika material och växtsystem som behandlas i detta arbete.



Nanotrådar i halvledarmaterial erbjuder möjligheter till flertalet applikationer, varav många enkla komponenter redan har demonstrerats. Utvecklingen av praktiska applikationer av sådana prototyper kan vara beroende utav möjligheten att förena nanotrådar i mer komplicerade strukturer. Den andra delen utav denna avhandling presenterar tekniker för tillverkning av tredimensionella, förgrenade nanotrådsstrukturer, inkluderat metoder för att uppnå kontrollerad struktur och morfologi. Tillverkning utav förgrenade strukturer i storskaligt ihopkopplade nätverk presenteras också. (Less)
Abstract
This thesis describes the epitaxial growth of III-V semiconductor nanowires using Au seed particles, and the design of more complex three-dimensional branched structures from these wires. Growth was performed by metallorganic vapour phase epitaxy, in which precursor molecules for the semiconductor material components are introduced in a low-pressure vapour. Nanowires grow epitaxially (with controlled crystal orientation) on a semiconductor substrate; diameter control is achieved via the Au particles, while length is controlled by growth parameters.



Particle-assisted nanowire growth is used extensively today to achieve well-controlled structures. The current understanding of this growth mechanism was developed over forty... (More)
This thesis describes the epitaxial growth of III-V semiconductor nanowires using Au seed particles, and the design of more complex three-dimensional branched structures from these wires. Growth was performed by metallorganic vapour phase epitaxy, in which precursor molecules for the semiconductor material components are introduced in a low-pressure vapour. Nanowires grow epitaxially (with controlled crystal orientation) on a semiconductor substrate; diameter control is achieved via the Au particles, while length is controlled by growth parameters.



Particle-assisted nanowire growth is used extensively today to achieve well-controlled structures. The current understanding of this growth mechanism was developed over forty years ago, and is known as the Vapour-Liquid-Solid (VLS) mechanism. This model indicates that a liquid alloy is formed between the seed particle and the growth material(s), and growth proceeds by precipitation from a supersaturated particle. The enhanced growth rate compared to the bulk growth from the vapour is typically attributed to preferential decomposition of precursor materials at or near the particle surface.



Recently, however, several inconsistencies have been observed between this model, which was developed for Au-assisted Si whiskers (micro-scale wires), and particle-assisted growth of other materials. In particular, there have been many reports of nanowire growth at temperatures too low for a liquid alloy to form. As well, nanowire growth has been reported for systems where no precursor molecules are used, and thus growth enhancement cannot be explained by preferential decomposition. Other reports have given evidence that such preferential decomposition does not necessarily occur when precursors are used. The first part of this thesis presents the current understanding of particle-assisted growth, both generally and for the specific materials and growth systems used here.



Semiconductor nanowires present the possibility for numerous applications, and many simple device components have been demonstrated. The development of practical applications of such prototypes may rely on the ability to assemble nanowires into more complex structures. The second part of this thesis presents techniques for the production of three-dimensional branched nanowire structures, including methods to achieve controlled structure and morphology. The assembly of branched structures into large-scale interconnected networks is also presented. (Less)
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author
supervisor
opponent
  • Professor Lieber, Charles, Harvard University, USA
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Natural science, III-V Semiconductor Materials, Fysik, Kondenserade materiens egenskaper:struktur, phase equilibria, crystallography, thermal and mechanical properties, Condensed matter:stucture, egenskaper (termiska och mekaniska), kristallografi, fasjämvikt, Naturvetenskap, Physics, Nanowires, Vapour Phase Epitaxy, Semiconductory physics, Halvledarfysik
pages
162 pages
defense location
Hall B Department of Physics Professorsgatan 1 Lund University Faculty of Engineering
defense date
2007-05-25 10:15
ISBN
978-91-628-7150-5
language
English
LU publication?
yes
id
beaace28-e93e-49a4-958e-93470efe753b (old id 548482)
date added to LUP
2007-09-28 09:51:42
date last changed
2016-09-19 08:45:19
@phdthesis{beaace28-e93e-49a4-958e-93470efe753b,
  abstract     = {This thesis describes the epitaxial growth of III-V semiconductor nanowires using Au seed particles, and the design of more complex three-dimensional branched structures from these wires. Growth was performed by metallorganic vapour phase epitaxy, in which precursor molecules for the semiconductor material components are introduced in a low-pressure vapour. Nanowires grow epitaxially (with controlled crystal orientation) on a semiconductor substrate; diameter control is achieved via the Au particles, while length is controlled by growth parameters.<br/><br>
<br/><br>
Particle-assisted nanowire growth is used extensively today to achieve well-controlled structures. The current understanding of this growth mechanism was developed over forty years ago, and is known as the Vapour-Liquid-Solid (VLS) mechanism. This model indicates that a liquid alloy is formed between the seed particle and the growth material(s), and growth proceeds by precipitation from a supersaturated particle. The enhanced growth rate compared to the bulk growth from the vapour is typically attributed to preferential decomposition of precursor materials at or near the particle surface.<br/><br>
<br/><br>
Recently, however, several inconsistencies have been observed between this model, which was developed for Au-assisted Si whiskers (micro-scale wires), and particle-assisted growth of other materials. In particular, there have been many reports of nanowire growth at temperatures too low for a liquid alloy to form. As well, nanowire growth has been reported for systems where no precursor molecules are used, and thus growth enhancement cannot be explained by preferential decomposition. Other reports have given evidence that such preferential decomposition does not necessarily occur when precursors are used. The first part of this thesis presents the current understanding of particle-assisted growth, both generally and for the specific materials and growth systems used here.<br/><br>
<br/><br>
Semiconductor nanowires present the possibility for numerous applications, and many simple device components have been demonstrated. The development of practical applications of such prototypes may rely on the ability to assemble nanowires into more complex structures. The second part of this thesis presents techniques for the production of three-dimensional branched nanowire structures, including methods to achieve controlled structure and morphology. The assembly of branched structures into large-scale interconnected networks is also presented.},
  author       = {Dick Thelander, Kimberly},
  isbn         = {978-91-628-7150-5},
  keyword      = {Natural science,III-V Semiconductor Materials,Fysik,Kondenserade materiens egenskaper:struktur,phase equilibria,crystallography,thermal and mechanical properties,Condensed matter:stucture,egenskaper (termiska och mekaniska),kristallografi,fasjämvikt,Naturvetenskap,Physics,Nanowires,Vapour Phase Epitaxy,Semiconductory physics,Halvledarfysik},
  language     = {eng},
  pages        = {162},
  school       = {Lund University},
  title        = {Epitaxial Growth and Design of Nanowires and Complex Nanostructures},
  year         = {2007},
}