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Magnetron Sputter Epitaxy of High-Quality GaN Nanorods on Functional and Cost-Effective Templates/Substrates
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0002-9796-8995
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0003-3203-7935
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
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2017 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 10, no 9, article id 1322Article in journal (Refereed) Published
Abstract [en]

We demonstrate the versatility of magnetron sputter epitaxy by achieving high-quality GaN nanorods on different substrate/template combinations, specifically Si, SiC, TiN/Si, ZrB2/Si, ZrB2/SiC, Mo, and Ti. Growth temperature was optimized on Si, TiN/Si, and ZrB2/Si, resulting in increased nanorod aspect ratio with temperature. All nanorods exhibit high purity and quality, proved by the strong bandedge emission recorded with cathodoluminescence spectroscopy at room temperature as well as transmission electron microscopy. These substrates/templates are affordable compared to many conventional substrates, and the direct deposition onto them eliminates cumbersome post-processing steps in device fabrication. Thus, magnetron sputter epitaxy offers an attractive alternative for simple and affordable fabrication in optoelectronic device technology.

Place, publisher, year, edition, pages
Basel, Switzerland: MDPI AG , 2017. Vol. 10, no 9, article id 1322
Keywords [en]
GaN, nanorods, Si, SiC, Ti, Mo, TiN and ZrB2 templates, magnetron sputtering, epitaxy
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:liu:diva-141597DOI: 10.3390/en10091322ISI: 000411225200078Scopus ID: 2-s2.0-85029362447OAI: oai:DiVA.org:liu-141597DiVA, id: diva2:1146156
Note

Funding agencies: Swedish Research Council (VR) [621-2012-4420, 621-2013-5360, 2016-04412]; Swedish Governmental Agency for Innovation Systems (VINNOVA) under the VINNMER international qualification program; Swedish Foundation for Strategic Research (SSF) through the Resea

Available from: 2017-10-02 Created: 2017-10-02 Last updated: 2018-05-03Bibliographically approved
In thesis
1. Magnetron Sputter Epitaxy of Group III-Nitride Semiconductor Nanorods
Open this publication in new window or tab >>Magnetron Sputter Epitaxy of Group III-Nitride Semiconductor Nanorods
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The III-nitride semiconductors family includes gallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN), and related ternary and quaternary alloys. The research interest on this group of materials is sparked by the direct bandgaps, and excellent physical and chemical properties. Moreover, the ternary alloys (InGaN, InAlN and AlGaN) present the advantage of bandgap tuning, giving access to the whole visible spectrum, from near infrared into deep ultraviolet wavelengths. The intrinsic properties of III-nitride materials can be combined with characteristical features of nanodimension and geometry in nanorod structures. Moreover, nanorods offer the advantage of avoiding problems arising from the lack of native substrates, like lattice and thermal expansion, film – substrate mismatch.

The growth and characterization of group III-nitride semiconductos nanorods, namely InAlN and GaN nanorods, is presented in this thesis. All the nanostructures were grown by employing direct-current reactive magnetron sputter epitaxy. InxAl1−xN self-assembled, core-shell nanorods on Si(111) substrates were demonstrated. A comprehensive study of temperature effect upon the morphology and composition of the nanorods was realized. The radial nanorod heterostructure consists of In-rich cores surrounded by Al-rich shells with different thicknesses. The spontaneous formation of core-shell nanorods is suggested to originate from phase separation due to spinodal decomposition. As the growth temperature increase, In desorption is favored, resulting in thicker Al-rich shells and larger nanorod diameters.

Both self-assembled and selective-area grown GaN nanorods are presented. Self-assembled growth of GaN nanorods on cost-effective substrates offers a cheaper alternative and simplifies device processing. Successful growth of high- quality GaN (exhibiting strong bandedge emission and high crystalline quality) on conductive templates/substrates such as Si, SiC, TiN/Si, ZrB2/Si, ZrB2/SiC, Mo, and Ti is supported by the possibility to be used as electrodes when integrated in optoelectronic devices.

The self-assembled growth leads to mainly random nucleation, resulting in nanorods with large varieties of diameters, heights and densities within a single growth run. This translates into non-uniform properties and complicates device processing. These problems can be circumvented by employing selective-area growth. Pre-patterned substrates by nano-sphere lithography resulted in GaN nanorods with controlled length, diameter, shape, and density. Well-faceted c-axis oriented GaN nanorods were grown directly onto the native SiOx layer inside nano-opening areas, exhibiting strong bandedge emission at room- temperature and single-mode lasing. Our studies on the growth mechanism revealed a different growth behavior when compared with selective-area grown GaN nanorods by MBE and MOCVD. The time-dependent growth series helped define a comprehensive growth mechanism from the initial thin wetting layer formed inside the openings, to the well-defined, uniform, hexagonal NRs resulted from the coalescence of multiple initial nuclei.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2017. p. 38
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1788
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-141595 (URN)10.3384/lic.diva-141595 (DOI)9789176854396 (ISBN)
Presentation
2017-10-13, Planck, Campus Valla, Linköping, 13:15 (English)
Opponent
Supervisors
Available from: 2017-10-02 Created: 2017-10-02 Last updated: 2017-10-11Bibliographically approved
2. Self-Assembled and Selective-Area Growth of Group III-Nitride Semiconductor Nanorods by Magnetron Sputter Epitaxy
Open this publication in new window or tab >>Self-Assembled and Selective-Area Growth of Group III-Nitride Semiconductor Nanorods by Magnetron Sputter Epitaxy
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The III-nitride semiconductor family includes gallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN), and the related ternary and quaternary alloys. The research interest on this group of materials is sparked by the direct bandgaps, and excellent physical and chemical properties. Moreover, the ternary alloys (InGaN, InAlN and AlGaN) present the advantage of bandgap tuning, giving access to the whole visible spectrum, from near infrared into deep ultraviolet wavelengths. The intrinsic properties of III-nitride materials can be combined with characteristic features of nanodimension and geometry in nanorod structures. Moreover, nanorods offer the advantage of avoiding problems arising from the lack of native substrates with film/substrate lattice and thermal expansion mismatch.

The growth and characterization of group III-nitride semiconductor nanorods, namely InAlN and GaN nanorods, is presented in this Thesis. All the nanostructures were grown by employing direct-current reactive magnetron sputter epitaxy. The results include the growth and study of both self-assembled and site-controlled grown nanorods.

InxAl1−xN self-assembled, core-shell nanorods on Si(111) substrates were demonstrated. A comprehensive study of temperature effect upon the morphology and composition of the nanorods was realized. The radial nanorod heterostructure consists of In-rich cores surrounded by Al-rich shells with different thicknesses. The spontaneous formation of core-shell nanorods is suggested to originate from phase separation due to spinodal decomposition. As the growth temperature increases, In desorption is favored, resulting in thicker Al-rich shells and larger nanorod diameters. Moreover, the in-plane crystallographic relationship of the nanorods and substrate was modified from a fiber-textured to an epitaxial growth by removing the native SiOx layer from the substrate.

Self-assembled growth of GaN nanorods on cost-effective substrates offers a cheaper alternative and simplifies device processing. Successful growth of high-quality GaN (exhibiting strong bandedge emission and high crystalline quality) on conductive templates/substrates such as Si, SiC, TiN/Si, ZrB2/Si, ZrB2/SiC, Mo, and Ti is supported by the possibility to be used as electrodes when integrated in optoelectronic devices. The influence of growth temperature upon the resulting size and optical properties of the nanorods was investigated. By applying a kinetic model, average diffusion length was calculated in correlation with growth temperature in order to explain the nanorods’ morphology evolution.

The self-assembled growth leads to random nucleation, resulting in nanorods with large varieties of diameters, heights and densities within a single growth run. This translates into non-uniform properties and complicates device processing. These problems can be circumvented by employing selective-area growth. Pre-patterned substrates by nanosphere lithography resulted in GaN nanorods with controlled length, diameter, shape, and density. Well-faceted caxis oriented GaN nanorods were grown directly onto the native SiOx layer inside opening areas exhibiting strong bandedge emission at room-temperature and single-mode lasing. The time-dependent growth series helped define a comprehensive growth mechanism from the initial thin wetting layer formed inside the openings, to the well-defined, uniform, hexagonal nanorods resulted from the coalescence of multiple initial nuclei.

Although nanosphere lithography is a fast and cheap patterning method, it does not offer the control on the size, position or density. The growth parameters were transferred onto focused ion beam lithography - patterned substrates which offers more control on the design. Focused ion beam lithography optimization included tailoring of the milling current (2-50 pA) and milling time (5-50 s). The patterning process optimisation enabled the minimization of mask and substrate damage, the key to attain uniform, welldefined, single, and straight nanorods. Destruction of the mask results in selective-area growth failure, while damage of the substrate surface promotes inclined nanorods grown into the openings, owning to random oriented nucleation. At lower growth temperatures (950 °C) nanostructures resulted from the coalescence of multiple, tilted, and irregular nanorods are observed. The tilting of the nanorods is reduced when increasing the growth temperature to 980 °C resulting in single and straight nanorods. The partial pressure of the Ar/N2 working gas was also varied for achieving selectivity and single nanorods, and study the growth behaviour. By increasing the amount of Ar in the working gas from 0 to 50%, we observe a transition of the target from a nitridized to metallic-state, affecting the sputtering conditions of the GaN nanorods. The change in the sputtering and deposition conditions influences the growth selectivity, coalescence, and growth rates. By balancing these effects, the selective growth of faceted, single nanorods was achieved.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2018. p. 47
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1935
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-147647 (URN)10.3384/diss.diva-147647 (DOI)9789176853085 (ISBN)
Public defence
2018-06-08, Schrödinger, E324, Fysikhuset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2018-05-03 Created: 2018-05-03 Last updated: 2018-05-03Bibliographically approved

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