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Valence Electron Energy Loss Spectroscopy of III-Nitride Semiconductors
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0003-3203-7935
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: urn:nbn:se:liu:diva-85907ISBN: 978-91-7519-746-3 (print)OAI: oai:DiVA.org:liu-85907DiVA: diva2:573698
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
List of papers
1. Standard-free composition measurements of Alx In1–xN by low-loss electron energy loss spectroscopy
Open this publication in new window or tab >>Standard-free composition measurements of Alx In1–xN by low-loss electron energy loss spectroscopy
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2011 (English)In: physica status solidi (RRL) – Rapid Research Letters, ISSN 1862-6270, Vol. 5, no 2, 50-52 p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate a standard-free method to retrieve compositional information in Alx In1–xN thin films by measuring the bulk plasmon energy (Ep), employing electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM). Two series of samples were grown by magnetron sputter epitaxy (MSE) and metal organic vapor phase epitaxy (MOVPE), which together cover the full com- positional range 0 ≤ x ≤ 1. Complementary compositional measurements were obtained using Rutherford backscattering spectroscopy (RBS) and the lattice parameters were obtained by X-ray diffraction (XRD). It is shown that Ep follows a linear relation with respect to composition and lattice parameter between the alloying elements from AlN to InN allowing for straightforward compositional analysis.

Place, publisher, year, edition, pages
Wiley, 2011
Keyword
AlInN;low-loss EELS;thin films;compositional analysis
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-65816 (URN)10.1002/pssr.201004407 (DOI)000288178300002 ()
Note
This is the pre-peer reviewed version of the following article: Justinas Palisaitis, Ching-Lien Hsiao, Muhammad Junaid, Mengyao Xie, Vanya Darakchieva, Jean-Francois Carlin, Nicolas Grandjean, Jens Birch, Lars Hultman and Per O.Å. Persson, Standard-free composition measurements of AlxIn1-xN by low-loss electron energy loss spectroscopy, 2011, physica status solidi (RRL) – Rapid Research Letters, (5), 2, 50-52. http://dx.doi.org/10.1002/pssr.201004407 Copyright: Wiley Available from: 2011-02-21 Created: 2011-02-21 Last updated: 2016-08-31
2. Effect of strain on low-loss electron energy loss spectra of group III-nitrides
Open this publication in new window or tab >>Effect of strain on low-loss electron energy loss spectra of group III-nitrides
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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
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-67981 (URN)10.1103/PhysRevB.84.245301 (DOI)000297767800004 ()
Available from: 2011-05-04 Created: 2011-05-04 Last updated: 2016-08-31Bibliographically approved
3. Spontaneous Formation of AlInN Core–Shell Nanorod Arrays by Ultrahigh-Vacuum Magnetron Sputter Epitaxy
Open this publication in new window or tab >>Spontaneous Formation of AlInN Core–Shell Nanorod Arrays by Ultrahigh-Vacuum Magnetron Sputter Epitaxy
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2011 (English)In: Applied Physics Express, ISSN 1882-0786, Vol. 4, no 115002Article in journal (Refereed) Published
Abstract [en]

The spontaneous formation of AlInN core–shell nanorod arrays with variable In concentration has been realized by ultrahigh-vacuum magnetron sputter epitaxy with Ti0.21Zr0.79N or VN seed layer assistance. The nanorods exhibit hexagonal cross sections with preferential growth along the c-axis. A core–shell rod structure with a higher In concentration in the core was observed by (scanning) transmission electron microscopy in combination with low-loss electron energy loss spectroscopy and energy dispersive X-ray spectroscopy. 5 K cathodoluminescence spectroscopy of Al0.86In0.14N nanorods revealed band edge emission at ∼5.46 eV, which was accompanied by a strong defect-related emission at ∼3.38 eV

Place, publisher, year, edition, pages
Japan Society of Applied Physics, 2011
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-73161 (URN)10.1143/APEX.4.115002 (DOI)000298289700028 ()
Note
Funding agencies|Swedish Strategic Foundation (SSF)||Available from: 2011-12-19 Created: 2011-12-19 Last updated: 2016-08-31
4. Curved-lattice epitaxial growth of chiral AlInN twisted nanorods for optical applications
Open this publication in new window or tab >>Curved-lattice epitaxial growth of chiral AlInN twisted nanorods for optical applications
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2012 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Despite of using chiral metamaterials to manipulate light polarization states has been demonstrated their great potential for applications such as invisible cloaks, broadband or wavelength-tunable circular polarizers, microreflectors, etc. in the past decade [1-6], operating wavelength in ultraviolet-visible range is still a challenge issue. Since these chiral structures often consist of metallic materials, their operation is designed for the infrared and microwave regions [2-4]. Here, we show how a controlled curved-lattice epitaxial growth (CLEG) of wide-bandgap AlInN semiconductor curved nanocrystals [7] can be exploited as a novel route for tailoring chiral nanostructures in the form of twisted nanorods (TNRs). The fabricated TNRs are shown to reflect light with a high degree of polarization as well as a high degree of circular polarization (that is, nearly circularly polarized light) in the ultravioletvisible region. The obtained polarization is shown to be dependent on the handedness of the TNRs.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-85902 (URN)
Available from: 2012-12-03 Created: 2012-12-03 Last updated: 2016-08-31Bibliographically approved
5. Characterization of InGaN/GaN quantum well growth using monochromated valence electron energy loss spectroscopy
Open this publication in new window or tab >>Characterization of InGaN/GaN quantum well growth using monochromated valence electron energy loss spectroscopy
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2014 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, no 3, 034302- p.Article in journal (Refereed) Published
Abstract [en]

The early stages of InGaN/GaN quantum wells growth for In reduced conditions have been investigated for varying thickness and composition of the wells. The structures were studied by monochromated STEM–VEELS spectrum imaging at high spatial resolution. It is found that beyond a critical well thickness and composition, quantum dots (>20 nm) are formed inside the well. These are buried by compositionally graded InGaN, which is formed as GaN is grown while residual In is incorporated into the growing structure. It is proposed that these dots may act as carrier localization centers inside the quantum wells.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-85903 (URN)10.1063/1.4861179 (DOI)000330615500062 ()
Note

On the day of the defence date the status of this article was Manuscript.

Available from: 2012-12-03 Created: 2012-12-03 Last updated: 2017-12-07Bibliographically approved
6. Thermal stability of Al1−xInxN (0 0 0 1) throughout the compositional range as investigated during in situ thermal annealing in a scanning transmission electron microscope
Open this publication in new window or tab >>Thermal stability of Al1−xInxN (0 0 0 1) throughout the compositional range as investigated during in situ thermal annealing in a scanning transmission electron microscope
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2013 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 61, no 12, 4683-4688 p.Article in journal (Refereed) Published
Abstract [en]

The thermal stability of Al1−xInxN (0 ⩽ ⩽ 1) layers was investigated by scanning transmission electron microscopy (STEM) imaging, electron diffraction, and monochromated valence electron energy loss spectroscopy during in situ annealing from 750 to 950 °C. The results show two distinct decomposition paths for the layers richest in In (Al0.28In0.72N and Al0.41In0.59N) that independently lead to transformation of the layers into an In-deficient, nanocrystalline and a porous structure. The In-richest layer (Al0.28In0.72N) decomposes at 750 °C, where the decomposition process is initiated by In forming at grain boundaries and is characterized by an activation energy of 0.62 eV. The loss of In from the Al0.41In0.59N layer was initiated at 800 °C through continuous desorption. No In clusters were observed during this decomposition process, which is characterized by an activation energy of 1.95 eV. Finally, layers richest in Al (Al0.82In0.18N and Al0.71In0.29N) were found to resist thermal annealing, although the initial stages of decomposition were observed for the Al0.71In0.29N layer.

Place, publisher, year, edition, pages
Elsevier, 2013
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-85904 (URN)10.1016/j.actamat.2013.04.043 (DOI)000321086100036 ()
Available from: 2012-12-03 Created: 2012-12-03 Last updated: 2017-12-07Bibliographically approved
7. Spinodal decomposition of Al0.3In0.7N(0001) layers following in-situ thermal annealing as investigated by STEM-VEELS
Open this publication in new window or tab >>Spinodal decomposition of Al0.3In0.7N(0001) layers following in-situ thermal annealing as investigated by STEM-VEELS
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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.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-85906 (URN)
Available from: 2012-12-03 Created: 2012-12-03 Last updated: 2016-08-31Bibliographically approved

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