Advanced

Analysis of Structure, Composition and Growth of Semiconductor Nanowires by Transmission Electron Microscopy

Ek, Martin LU (2013)
Abstract (Swedish)
Popular Abstract in Swedish

Nanotrådar har potential att bli en mycket flexibel plattform för design av halvledarkomponenter. I nanotrådar är det möjligt att bilda kristallstrukturer som normalt sett inte förekommer i bulkmaterial, och att kombinera olika III-V och grupp IV material i axiella eller radiella heterostrukturer. Eftersom så pass komplicerade strukturer kan skapas, både avsiktligt och oavsiktligt, är karakterisering av kristallstruktur och sammansättning mycket viktigt. I den här avhandlingen presenteras olika transmissionselektronmikroskopimetoder för detta syftet.



Högupplöst transmissionselektronmikroskopi kan direkt avbilda kristallstrukturen, inklusive eventuella tvillingar och stapelfel.... (More)
Popular Abstract in Swedish

Nanotrådar har potential att bli en mycket flexibel plattform för design av halvledarkomponenter. I nanotrådar är det möjligt att bilda kristallstrukturer som normalt sett inte förekommer i bulkmaterial, och att kombinera olika III-V och grupp IV material i axiella eller radiella heterostrukturer. Eftersom så pass komplicerade strukturer kan skapas, både avsiktligt och oavsiktligt, är karakterisering av kristallstruktur och sammansättning mycket viktigt. I den här avhandlingen presenteras olika transmissionselektronmikroskopimetoder för detta syftet.



Högupplöst transmissionselektronmikroskopi kan direkt avbilda kristallstrukturen, inklusive eventuella tvillingar och stapelfel. Eftersom III-V materialen är polära finns det ytterligare en parameter att bestämma. För att utläsa polaritet från högupplösta bilder räcker det inte att förbättra upplösningen med hjälp av aberrationskorrigering, utan provets lokala orientering måste också bestämmas. Elektrondiffraktion med konvergent stråle är en alternativ metod som ställer mycket lägre krav på mikroskop och mikroskopist, och som går att anpassa till de flesta material och kristallstrukturer.



Transmissionselektronmikroskopi erbjuder dessutom flera metoder för att bestämma och kartlägga nanotrådarnas sammansättning. Oavsett metod är det mycket viktigt att undvika att nanotrådarna skadas under tiden den analytiska signalen samlas in. För den mest använda metoden, energidispersiv röntgenspektroskopi, kan detta åstadkommas genom att sprida elektrondosen över ett så stort område som möjligt. Om sammansättningen bara har en okänd parameter kan alternativa metoder, till exempel ändringar i energi för plasmoner, användas istället då de utnyttjar signalerna som bildas då elektronerna interagerar med provet på ett mer effektivt sätt.



För att förbättra nanotrådarnas kristallstruktur och sammansättning måste dessa kopplas till de dynamiska processer som sker då kristallerna växes fram. I undantagsfall är det möjligt att dra slutsatser kring dessa processer utifrån de färdiga nanotrådarna, men idealet hade varit att observera de växande nanotrådarna in-situ i mikroskopet. Detta är vanligtvis endast möjligt med mycket specialiserade mikroskop. I den här avhandlingen demonstreras dock växt i slutna celler med elektrontransparenta fönster. Även om tillståndet inne i cellerna under själva växten inte kunde mätas eller styras exakt, så möjliggjorde de slutna cellerna att växt av InAs-nanotrådar kunde studeras för första gången, och dessutom i ett konventionellt transmissionselektronmikroskop. (Less)
Abstract
Nanowires have the potential to be a very flexible platform for the design of semiconductor devices. In nanowires it is possible to form crystal structures not found in the bulk materials under normal conditions, and to combine different III-V and group IV materials into axial or radial heterostructures. As quite complex structures can be formed, both intentionally and unintentionally, characterization of the crystal structure and composition is important. In this thesis, various transmission electron microscopy techniques are presented for this purpose.



High resolution imaging can directly visualize the crystal structure, including twinning and stacking faults. The polar nature of the III-V materials leaves one more... (More)
Nanowires have the potential to be a very flexible platform for the design of semiconductor devices. In nanowires it is possible to form crystal structures not found in the bulk materials under normal conditions, and to combine different III-V and group IV materials into axial or radial heterostructures. As quite complex structures can be formed, both intentionally and unintentionally, characterization of the crystal structure and composition is important. In this thesis, various transmission electron microscopy techniques are presented for this purpose.



High resolution imaging can directly visualize the crystal structure, including twinning and stacking faults. The polar nature of the III-V materials leaves one more parameter to be determined. In order to determine polarity from high resolution images it is not only necessary to improve the resolution further by aberration correction, but in addition the local orientation of the sample must be determined. Convergent beam electron diffraction is an alternative method with much lower demands on the microscope and operator, and can be adapted to suit most materials and crystal structures.



Transmission electron microscopy also provides several methods for determining and mapping the composition of the nanowires. It is important in all cases to avoid damaging the nanowires during the acquisition of the analytical signal. In the most commonly used method, energy dispersive X-ray spectroscopy, this can be achieved by spreading the electron dose over as large an area as possible. If there is only a single unknown parameter for the composition, alternative methods such as the shift in plasmon energy with composition can be used instead, as they have higher collection efficiencies.



In order to improve the nanowires in terms of crystal structure and composition, these must be connected to the dynamic processes occurring during growth. Occasionally these processes can be inferred from the fully formed nanowires after growth, but ideally one would like to observe the growth in-situ in the microscope. This is usually possible only with highly specialized environmental microscopes. In this thesis, nanowire growth in much simpler closed cells is demonstrated. Although the growth conditions could neither be precisely measured nor controlled, the closed cells made it possible to observe for the first time growing InAs nanowires in-situ in a conventional transmission electron microscope. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Prof. Arbiol, Jordi, Institut de Ciència de Materials de Barcelona
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Transmission electron microscopy, nanowires, III-V semiconductors, polarity, in-situ TEM
pages
191 pages
publisher
Centre for Analysis and Synthesis
defense location
Lecture hall B, Kemicentrum, Getingevägen 60, Lund University Faculty of Engineering
defense date
2014-01-31 13:00
ISBN
978-91-7422-340-8
language
English
LU publication?
yes
id
a9266c69-68dd-4289-b3b9-d1ff00c935ae (old id 4221852)
date added to LUP
2014-01-02 11:22:54
date last changed
2016-09-19 08:45:06
@misc{a9266c69-68dd-4289-b3b9-d1ff00c935ae,
  abstract     = {Nanowires have the potential to be a very flexible platform for the design of semiconductor devices. In nanowires it is possible to form crystal structures not found in the bulk materials under normal conditions, and to combine different III-V and group IV materials into axial or radial heterostructures. As quite complex structures can be formed, both intentionally and unintentionally, characterization of the crystal structure and composition is important. In this thesis, various transmission electron microscopy techniques are presented for this purpose. <br/><br>
<br/><br>
High resolution imaging can directly visualize the crystal structure, including twinning and stacking faults. The polar nature of the III-V materials leaves one more parameter to be determined. In order to determine polarity from high resolution images it is not only necessary to improve the resolution further by aberration correction, but in addition the local orientation of the sample must be determined. Convergent beam electron diffraction is an alternative method with much lower demands on the microscope and operator, and can be adapted to suit most materials and crystal structures. <br/><br>
<br/><br>
Transmission electron microscopy also provides several methods for determining and mapping the composition of the nanowires. It is important in all cases to avoid damaging the nanowires during the acquisition of the analytical signal. In the most commonly used method, energy dispersive X-ray spectroscopy, this can be achieved by spreading the electron dose over as large an area as possible. If there is only a single unknown parameter for the composition, alternative methods such as the shift in plasmon energy with composition can be used instead, as they have higher collection efficiencies. <br/><br>
<br/><br>
In order to improve the nanowires in terms of crystal structure and composition, these must be connected to the dynamic processes occurring during growth. Occasionally these processes can be inferred from the fully formed nanowires after growth, but ideally one would like to observe the growth in-situ in the microscope. This is usually possible only with highly specialized environmental microscopes. In this thesis, nanowire growth in much simpler closed cells is demonstrated. Although the growth conditions could neither be precisely measured nor controlled, the closed cells made it possible to observe for the first time growing InAs nanowires in-situ in a conventional transmission electron microscope.},
  author       = {Ek, Martin},
  isbn         = {978-91-7422-340-8},
  keyword      = {Transmission electron microscopy,nanowires,III-V semiconductors,polarity,in-situ TEM},
  language     = {eng},
  pages        = {191},
  publisher    = {ARRAY(0xc39a040)},
  title        = {Analysis of Structure, Composition and Growth of Semiconductor Nanowires by Transmission Electron Microscopy},
  year         = {2013},
}