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Effect of strain on low-loss electron energy loss spectra of group III-nitrides
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. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
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2011 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 24, 245301- p.Article in journal (Refereed) Published
Abstract [en]

Low-loss EELS was used to acquire information about the strain state in group III-nitrides. Experimental and theoretical simulation results show that the bulk plasmon peak position varies near linearly with unit cell volume variations due to strain. A unit cell volume change of 1% results in a bulk plasmon peak shift of 0.159 eV, 0.168 eV, and 0.079 eV for AlN, GaN, and InN, respectively, according to simulations. The AlN peak shift was experimentally corroborated with a peak shift of 0.156 eV, where the applied strain caused a 1% volume change. It is also found that while the bulk plasmon energy can be used as a measure of the composition in a III-nitride alloy for relaxed structures, the presence of strain significantly affects such a measurement. The strain has a lower impact on the peak shift for Al(1-x)InxN (3% compositional error per 1 % volume change) and In(1-x)GaxN alloys compared to significant variations for Al(1-x)GaxN (16% compositional error for 1% volume change). Hence low-loss studies off III-nitrides, particularly for confined structures, must be undertaken with care and understanding.

Place, publisher, year, edition, pages
American Physical Society , 2011. Vol. 84, no 24, 245301- p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-67981DOI: 10.1103/PhysRevB.84.245301ISI: 000297767800004OAI: oai:DiVA.org:liu-67981DiVA: diva2:414770
Available from: 2011-05-04 Created: 2011-05-04 Last updated: 2016-08-31Bibliographically approved
In thesis
1. Electron Energy Loss Spectroscopy of III-Nitride Semiconductors
Open this publication in new window or tab >>Electron Energy Loss Spectroscopy of III-Nitride Semiconductors
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This Licentiate Thesis covers experimental and theoretical investigations of the bulk plasmon response to different compositions and strain states of group III-nitride materials. Investigated materials were grown using magnetron sputtering epitaxy and metal organic chemical vapour deposition and studied by Rutherford backscattering spectrometry, X-ray diffraction, electron microscopy and electron energy loss spectroscopy (EELS).

It is shown that low-loss EELS is a powerful method for a fast compositional determination in AlxIn1-xN system. The bulk plasmon energy of the investigated material system follows a linear relation with respect to lattice parameter and composition in unstrained layers.

Furthermore, the effect of strain on the bulk plasmon peak position has been investigated by using low-loss EELS in group III-nitrides. We experimentally determine the AlN bulk plasmon peak shift of 0.156 eV per 1% volume change. The AlN peak shift was corroborated by full potential calculations (Wein2k), which reveal that the bulk plasmon peak position of III-nitrides varies near linearly with unit cell volume variations.

Finally, self-assembled ternary Al1-xInxN nanorod arrays with variable In concentration have been realized onto c-plane sapphire substrates by ultra-high-vacuum magnetron sputtering epitaxy with Ti0.21Zr0.79N or VN seed layer assistance. The nanorods exhibit hexagonal cross-sections with preferential growth along the Al1-xInxN c-axis. A coaxial rod structure with higher In concentration in the core was observed by scanning transmission electron microscopy in combination with low-loss EELS.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2011. 47 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1487
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-67985 (URN)LIU-TEK-LIC-2011:26 (Local ID)978-91-7393-161-8 (ISBN)LIU-TEK-LIC-2011:26 (Archive number)LIU-TEK-LIC-2011:26 (OAI)
Presentation
2011-06-01, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2011-05-04 Created: 2011-05-04 Last updated: 2016-08-31Bibliographically approved
2. 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-LienBirch, JensHultman, LarsPersson, Per O.Å.
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