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Spinodal decomposition of Al0.3In0.7N(0001) layers following in-situ thermal annealing as investigated by STEM-VEELS
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0003-3203-7935
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0002-2837-3656
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
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2012 (English)Manuscript (preprint) (Other academic)
Abstract [en]

The thermal stability and spinodal decomposition of thin Al0.3In0.7N layers was studied in-situ by scanning transmission electron microscopy following annealing in a temperature range from 700 oC to 900 oC. The results show that for increasing layer thicknesses (from ~4 nm to ~22 nm) surface directed spinodal decomposition is initiated at Al0.3In0.7N/AlN interfaces and columnar boundaries in the Al0.3In0.7N layers. In the thin layers (~10 nm) annealing caused a single composition layer to split into doubly modulated layers with a compositional undulation perpendicular to the interfaces, while for the thicker layers (~22 nm) the spinodally decomposed structure is more random.

Place, publisher, year, edition, pages
2012.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-85906OAI: oai:DiVA.org:liu-85906DiVA: diva2:573690
Available from: 2012-12-03 Created: 2012-12-03 Last updated: 2016-08-31Bibliographically approved
In thesis
1. Valence Electron Energy Loss Spectroscopy of III-Nitride Semiconductors
Open this publication in new window or tab >>Valence Electron Energy Loss Spectroscopy of III-Nitride Semiconductors
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This doctorate thesis covers both experimental and theoretical investigations of the optical responses of the group III-nitrides (AlN, GaN, InN) and their ternary alloys. The goal of this research has been to explore the usefulness of valence electron energy loss spectroscopy (VEELS) for materials characterization of group III-nitride semiconductors at the nanoscale. The experiments are based on the evaluation of the bulk plasmon characteristics in the low energy loss part of the EEL spectrum since it is highly dependent on the material’s composition and strain. This method offers advantages as being fast, reliable, and sensitive. VEELS characterization results were corroborated with other experimental methods like X-ray diffraction and Rutherford backscattering spectrometry as well as full-potential calculations (Wien2k). Investigated III-nitride structures were grown using magnetron sputtering epitaxy and metal organic chemical vapor deposition techniques.

Initially, it was demonstrated that EELS in the valence region is a powerful method for a fast compositional analysis of the Al1-xInxN (0≤x≤1) system. The bulk plasmon energy follows a linear relation with respect to the lattice parameter and composition in Al1-xInxN layers. Furthermore, the effect of strain on valence EELS was investigated. It was experimentally determined that the AlN bulk plasmon peak experiences a shift of 0.156 eV per 1% volume change at constant composition. The experimental results were corroborated by full-potential calculations, which showed that the bulk plasmon peak position varies nearly linearly with the unit-cell volume, at least up to 3% volume change.

Employing the bulk plasmon energy loss, compositional characterization was also applied to confined structures, such as nanorods and quantum wells (QWs). Compositional profiling of spontaneously formed AlInN nanorods with varying In concentration was realized in cross-sectional and plan-view geometries. It was established that the structures exhibit a core-shell structure, where the In concentration in the core is higher than in the shell. The growth of InGaN/GaN multiple QWs with respect to composition and interface homogeneities was investigated. It was found that at certain compositions and thicknesses of QWs, where phase separation does not occur due to spinodal decomposition. Instead, QWs develop quantum dot like features inside the well as a consequence of Stranski-Krastanov-type growth mode, and delayed In incorporation into the structure.

The thermal stability and degradation mechanisms of Al1-xInxN (0≤x≤1) films with different In contents, stacked in a multilayer sample, and different periodicity Al1-xInxN/AlN multilayer films, was investigated by performing a thermal annealing in combination with VEELS mapping in-situ. It was concluded that the In content in the Al1-xInxN layer determines the thermal stability and decomposition path. Finally, the phase separation by spinodal decomposition of different periodicity AlInN/AlN layers, with a starting composition inside the miscibility gap, was explored.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. 74 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1488
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-85907 (URN)978-91-7519-746-3 (ISBN)
Public defence
2012-12-14, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2012-12-03 Created: 2012-12-03 Last updated: 2016-08-31Bibliographically approved

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Palisaitis, JustinasHsiao, Ching-LienHultman, LarsBirch, JensPersson, Per

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