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Nucleation and initial growth of sp2-BNon α-Al2O3 and SiC by chemical vapour deposition
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.ORCID iD: 0000-0002-7171-5383
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Hungarian Academic Science, Hungary .
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2014 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Knowledge on thin films evolution from the early stages of growth is important for the control of quality and properties of the film. Here we present study of the early growth stages and evolution of the crystalline structure of sp2 hybridised Boron Nitride (BN) thin films deposited by chemical vapour deposition from triethyl boron and ammonia. Nucleation of hexagonal BN (h-BN) is observed already at 1200 °C on α-Al2O3 substrate with an AlN buffer layer (AlN/α-Al2O3) while no formation of h-BN is detected when the growth is done on 6H-SiC in a growth temperature range between 1200 °C and 1700 °C. We demonstrate that h-BN grows on AlN/α-Al2O3 exhibiting a layer-by-layer growth mode up to ca. 4 nm followed by a transition to r-BN growth when grown at 1500 °C. The following r-BN growth is suggested to proceed with mixed layer-by-layer and island growth mode; after a thin continuous layer of r-BN, islands formation is favoured leading to a twinned r-BN structure of the film. We find that h-BN does not grow on 6H-SiC substrates instead r-BN nucleates and grows directly as a twinned crystal. The twinning is found to be suppressed by a surface preparation of the SiC substrate with SiH4 prior to BN growth. These results open up for a more controlled epitaxial growth of sp2-BN for future electronic applications.

Place, publisher, year, edition, pages
2014.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-112578OAI: oai:DiVA.org:liu-112578DiVA: diva2:768465
Available from: 2014-12-04 Created: 2014-12-04 Last updated: 2015-03-11Bibliographically approved
In thesis
1. Chemical Vapour Deposition of sp2 Hybridised Boron Nitride
Open this publication in new window or tab >>Chemical Vapour Deposition of sp2 Hybridised Boron Nitride
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The aim of this work was to develop a chemical vapour deposition process and understand the growth of sp2 hybridised Boron Nitride (sp2-BN). Thus, the growth on different substrates together with the variation of growth parameters was investigated in details and is presented in the papers included in this thesis. Deposited films of sp2-BN were characterised with the purpose to determine optimal deposition process parameters for the growth of high crystal quality thin films with further investigations of chemical composition, morphology and other properties important for the implementation of this material towards electronic, optoelectronic devices and devices based on graphene/BN heterostructures.

For the growth of sp2-BN triethyl boron and ammonia were employed as B and N precursors, respectively. Pure H2 as carrier gas is found to be necessary for the growth of crystalline sp2-BN. Addition of small amount of silane to the gas mixture improves the crystalline quality of the growing sp2-BN film.

It was observed that for the growth of crystalline sp2-BN on c-axis oriented α-Al2O3 a thin and strained AlN buffer layer is needed to support epitaxial growth of sp2-BN, while it was possible to deposit rhombohedral BN (r-BN) on various polytypes of SiC without the need for a buffer layer. The growth temperature suitable for the growth of  crystalline sp2-BN is 1500 °C. Nevertheless, the growth of crystalline sp2-BN was also observed on α-Al2O3 with an AlN buffer layer at a lower temperature of 1200 °C. Growth at this low temperature was found to be hardly controllable due to the low amount of Si that is necessary at this temperature and its accumulation in the reaction cell. When SiC was used as a substrate at the growth temperature of 1200 °C, no crystalline sp2-BN was formed, according to X-ray diffraction.

Crystalline structure investigations of the deposited films showed formation of twinned r-BN on both substrates used. Additionally, it was found that the growth on α-Al2O3 with an AlN buffer layer starts with the formation of hexagonal BN (h-BN) for a thickness of around 4 nm. The formation of h-BN was observed at growth temperatures of 1200 °C and 1500 °C on α-Al2O3 with AlN buffer layer while there were no traces of h-BN found in the films deposited on SiC substrates in the temperature range between 1200 °C and 1700 °C. As an explanation for such growth behaviour, reproduction of the substrate crystal stacking is suggested.  Nucleation and growth mechanism are investigated and presented in the papers included in this thesis.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. 54 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1632
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-112580 (URN)10.3384/diss.diva-112580 (DOI)978-91-7519-193-5 (ISBN)
Public defence
2015-02-10, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 09:15 (English)
Opponent
Supervisors
Available from: 2014-12-04 Created: 2014-12-04 Last updated: 2015-03-11Bibliographically approved

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Pedersen, HenrikHögberg, HansAndersson, Sven G.Henry, Anne

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