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Characterization of high-quality free-standing GaN grown by HVPE
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. Linköping University, The Institute of Technology.
Research Institute for Technical Physics and Materials Science of the Hungarian Academy of Sci., Budapest, Hungary .
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2004 (English)In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T114, 18-21 p.Article in journal (Refereed) Published
Abstract [en]

Single-crystalline 330µm thick GaN has been grown on 2'' Al2O3 (0 0 0 1) by hydride vapour phase epitaxy (HVPE). Upon laser-induced lift-off the GaN was delaminated from the sapphire substrate, and bulk-like free-standing GaN was achieved. Various characterization methods were utilized to assess the structural and optical quality of the freestanding material. The X-ray rocking curves of the (1 0–1 4) and (0 0 0 2) diffraction peaks revealed full width at half maximum (FWHM) values of 96 and 129arcsec, respectively. These data compare well with the smallest corresponding values published so far for bulk-like HVPE-GaN. The dislocation density determined by plan-view transmission electron microscopy studies is 1–2 × 107cm–2. The low-temperature near-band-gap photoluminescence spectrum shows the main donor bound exciton (DBE) peak at 3.4718eV with a FWHM of 1.4meV, verifying the high crystalline quality of the bulk-like GaN. The DBE peak position suggests complete stress relief. The phonon spectra measured by infrared spectroscopic ellipsometry confirm as well, that the free-standing material is of high crystalline quality and virtually stress-free.

Place, publisher, year, edition, pages
2004. Vol. T114, 18-21 p.
National Category
Engineering and Technology
URN: urn:nbn:se:liu:diva-48267DOI: 10.1088/0031-8949/2004/T114/004OAI: diva2:269163
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2012-11-29
In thesis
1. Growth of thick GaN layers on sapphire by Hydride Vapour Phase Epitaxy
Open this publication in new window or tab >>Growth of thick GaN layers on sapphire by Hydride Vapour Phase Epitaxy
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Gallium nitride (GaN) is a wide bandgap material that is already extensively used in industrial production of optoelectronic devices (light emitters) that operate in the blue and ultraviolet wavelength range. GaN is interesting not only because it has a wide bandgap (3.5 eV), it is also chemically and physically inert and is environmental friendly for device production, as opposed to the lower bandgap III-V materials based on GaAs or InP.

Despite recent efforts there is still no bulk GaN substrates with sufficient crystal quality and size and sufficiently low price that they can be used commercially in devices. The problem in growing GaN is that because there are no native substrates the growth is done on foreign substrates (heteroepitaxy). When GaN is grown heteroepitaxially there will be a built in strain in the material because of the lattice mismatch and thermal expansion difference between the materials. This produces a number of different defects that degrades the crystal quality. Native GaN substrates are therefore strongly in demand, and many growth techniques are presently pursued worldwide to develop such substrates.

Hydride Vapor Phase Epitaxy (HVPE) is the growth technique most commonly used for growing bulk GaN material. Certainly it is the most developed method, and it can produce a high growth rate(> 100 μ/hr). HVPE has comparatively simple growth chemistry and is relatively economic compared to other growth techniques.

In the work involved in this PhD thesis the focus has been to optimize the growth of thick 2" diameter GaN layers on sapphire with a vertical HVPE system.

Paper I deal with how to grow thick GaN layers(> 300 μm) on sapphire, and reviews some of the problems that are involved in the growth process. The emphasis is on the growth related defects in such thick GaN layers.

In Paper II we have shown that it is possible to grow GaN with a very high growth rate and with good crystal quality.

Paper III shows that it is possible to produce a free-standing GaN layer that is strain free. This is done by separating the GaN layer from the sapphire substrate using a laser lift-off (LLO) process.

In paper IV the optical and structural properties of thick freestanding GaN layers are reported.

In paper V we have shown that it is possible to grow a GaN layer on sapphire over a 2" area that is virtually strain free over most part of the grown area. This is due to induced cracking in the starting sapphire substrate during the cool down phase.

In paper VI we have grown the GaN material on a starting template consisting of a two-step epitaxial lateral overgrowth (ELO) GaN layer grown by MOVPE on a sapphire substrate. The self separated GaN layer was then evaluated and the result showed a virtually strain free material.

In paper VII positron annihilation studies of a thick GaN layer is performed. The studies were done to identify native point defects (Ga vacancies) in the as-grown non-intentionally doped n-type GaN.

Paper VIII deals with μ-Raman scattering profiling studies on a thick free-standing GaN layer. The studies provided the vertical strain distribution and the evolution of the crystalline quality with increasing layer thickness.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2005. 45 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 958
National Category
Natural Sciences
urn:nbn:se:liu:diva-31201 (URN)16949 (Local ID)91-85299-75-8 (ISBN)16949 (Archive number)16949 (OAI)
Public defence
2005-06-15, Hörsal Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (Swedish)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2012-11-29

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