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Liquid-target Reactive Magnetron Sputter Epitaxy of High Quality GaN(0001ɸ)ɸ Nanorods on Si(111)
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.
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.
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2015 (English)In: Materials Science in Semiconductor Processing, ISSN 1369-8001, E-ISSN 1873-4081, Vol. 39, 702-710 p.Article in journal (Refereed) Published
Abstract [en]

Direct current magnetron sputter epitaxy with a liquid Ga sputtering target hasbeen used to grow single-crystal GaN(0001) nanorods directly on Si(111)substrates at different working pressures ranging from 5 to 20 mTorr of pure N2,.The as-grown GaN nanorods exhibit very good crystal quality from bottom to topwithout stacking faults, as determined by transmission electron microscopy. Thecrystal quality is found to increase with increasing working pressure. X-raydiffraction results show that all the rods are highly (0001)-oriented. Thenanorods exhibit an N-polarity, as determined by convergent beam electrondiffraction methods. Sharp and well-resolved 4 K photoluminescence peaks at ~3.474 eV with a FWHM ranging from 1.7 meV to 35 meV are attributed to theintrinsic GaN band edge emission and corroborate the superior structuralproperties of the material. Texture measurements reveal that the rods haverandom in-plane orientation when grown on Si(111) with native oxide, while theyhave an in-plane epitaxial relationship of GaN[110] // Si[110] when grown onsubstrates without surface oxide.

Place, publisher, year, edition, pages
Elsevier, 2015. Vol. 39, 702-710 p.
Keyword [en]
GaN, Nanorods, X-ray Diffraction, TEM, PL, magnetron sputter epitaxy, sputtering
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-84653DOI: 10.1016/j.mssp.2015.05.055ISI: 000361774100097OAI: oai:DiVA.org:liu-84653DiVA: diva2:560991
Note

Funding: Swedish Foundation for Strategic Research; Swedish Research Council Linnaeus [2008-6572]; Swedish Government Strategic Research Area Grant in Materials Science AFM-SFO MatLiU [2009-00971]; Knut and Alice Wallenberg Foundation

Available from: 2012-10-16 Created: 2012-10-16 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Magnetron Sputter Epitaxy of GaN Epilayers and Nanorods
Open this publication in new window or tab >>Magnetron Sputter Epitaxy of GaN Epilayers and Nanorods
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this research, electronic-grade GaN(0001) epilayers and nanorods have been grown onto Al2O3(0001) and Si(111) substrates, respectively, by reactive magnetron sputter epitaxy (MSE) using liquid Ga as a sputtering target. MSE, employing ultra high vacuum conditions, high-purity source materials, and lowenergy ion assisted deposition from substrate biasing, is a scalable method, lending itself to large area GaN synthesis.

For the growth of epitaxial GaN films two types of sputtering techniques, direct current (DC) magnetron sputtering and high power impulse magnetron sputtering (HiPIMS) were studied. The GaN epitaxial films grown by DC-MSE directly on to Al2O3(0001) in a mixture of Ar and N2, feature low threading dislocation densities on the order of ≤ 1010 cm-2, as determined by transmission electron microscopy (TEM) and modified Williamson-Hall plots. X-ray rocking curves reveal a narrow full-width at half maximum (FWHM) of 1054 arcsec of the 0002 reflection. A sharp 4 K photoluminescence (PL) peak at 3.474 eV with a FWHM of 6.3 meV is attributed to intrinsic GaN band edge emission. GaN(0001) epitaxial films grown on Al2O3 substrates by HiPIMS deposition in a mixed N2/Ar discharge contain both strained domains and almost relaxed domains in the same epilayers, which was determined by a combination of x-ray diffraction (XRD), TEM, atomic force microscopy (AFM), μ-Raman microscopy, μ-PL, and Cathodoluminescence (CL). The almost fully relaxed domains show superior structural and optical properties evidenced by a rocking curves with full width at half maximum of 885 arc sec and a low temperature band edge luminescence at 3.47 eV with the FWHM of 10 meV. The other domain exhibits a 14 times higher isotropic strain component, which is due to higher densities of point and extended defects, resulting from  bombardment of energetic species during growth.

Single-crystal GaN(0001) nanorods have been grown directly on Si(111) substrates by DC-MSE in a pure N2environment. The as-grown GaN nanorods exhibit very high crystal quality from bottom to the top without any stacking faults, as determined by TEM. The crystal quality is found to increase with increasing working pressure. XRD results show that all the rods are highly 0001 oriented. All nanorods exhibit an N-polarity, as determined by convergent beam electron diffraction methods. Sharp and well-resolved 4 K μ-PL peaks at ~3.474 eV with a FWHM ranging from 1.7 meV to 22 meV are attributed to the intrinsic GaN band edge emission and corroborate the exceptional crystal quality of the material. Texture measurements reveal that the rods have random in-plane orientation when grown on Si(111) with its native oxide while they have an inplane epitaxial relationship of GaN[11̅20] // Si[1̅10] when grown on Si(111) without the surface oxide. The best structural and optical properties of the rods were achieved at N2 partial pressures of 15 to 20 mTorr. By diluting the reactive N2 working gas in DC-MSE with Ar, it is possible to achieve favorable growth conditions for high quality GaN nanorods onto Si(111) at a low total pressure of 5 mTorr. With an addition of small amount of Ar (0.5 mTorr), we observe an increase in nanorod aspect ratio from 8 to ~35, a decrease in average diameter from 74 nm to 35 nm, and a 2-fold increase in nanorod density compared to pure N2 conditions. By further dilution, the aspect ratio continuously decreases to 14 while the diameter increases to 60 nm and the nanorod density increases to a maximum of 2.4×109 cm-1. The changes in nanorod morphology upon Ar-dilution of the N2 working gas are explained by a transition from N-rich growth conditions, promoting the diffusion induced nanorods growth mode, to Ga-rich growth conditions, in qualitative agreement with GaN nanorods growth by MBE. At N2 partial pressure of 2.5 mTorr, the Ga-target is close to a non-poisoned state which gives the most perfect crystal quality which is reflected in an exceptionally narrow band edge emission at 3.479 eV with a FWHM of only 1.7 meV. Such structural and optical properties are comparable to rods previously grown at 3 to 4 time higher total working pressures of pure N2.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. 66 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1482
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-84655 (URN)978-91-7519-782-1 (ISBN)
Public defence
2012-11-05, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
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Available from: 2012-10-16 Created: 2012-10-16 Last updated: 2016-08-31Bibliographically approved

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Muhammad, JunaidChen, Yen-TingPalisaitis, JustinasGarbrecht, MagnusHsiao, Ching-LienPersson, PerHultman, LarsBirch, Jens

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