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Growth of thick GaN layers on sapphire by Hydride Vapour Phase Epitaxy
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
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.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 958
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-31201Local ID: 16949ISBN: 91-85299-75-8 (print)OAI: oai:DiVA.org:liu-31201DiVA: diva2:252024
Public defence
2005-06-15, Hörsal Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (Swedish)
Opponent
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2012-11-29
List of papers
1. Growth of thick GaN layers with hydride vapour phase epitaxy
Open this publication in new window or tab >>Growth of thick GaN layers with hydride vapour phase epitaxy
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2005 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 281, no 1, 17-31 p.Article in journal (Refereed) Published
Abstract [en]

In this paper we describe recent experimental efforts to produce high quality thick (⩾300 μm) GaN layers on sapphire, the removal of such a layer from the sapphire substrate, and the properties of the so obtained free-standing GaN material. The growth process is described in some detail in the vertical reactor geometry used in this work. Defects like dislocations, micro-cracks and pits produced during growth are discussed, along with procedures to minimize their concentration on the growing surface. The laser lift-off technique is shown to be a feasible technology, in particular if a powerful laser with a large spot size can be used. A major problem with the free-standing material is the typically large bowing of such a wafer, due to the built in defect concentrations near the former GaN-sapphire interface. This bowing typically causes a rather large width of the XRD rocking curve of the free-standing material, while optical data confirm virtually strain free material of excellent quality at the top surface.

Keyword
characterization, computer simulation, defects, chloride vapour phase deposition, gallium nitride
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-46086 (URN)10.1016/j.jcrysgro.2005.03.040 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
2. Fast growth of high quality GaN
Open this publication in new window or tab >>Fast growth of high quality GaN
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2003 (English)In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 200, no 1, 13-17 p.Article in journal (Refereed) Published
Abstract [en]

We have grown bulk-like GaN with a thickness up to 335 μm on 2″ sapphire substrates in a vertical HVPE reactor with a bottom-fed design. A very high growth rate of 250 μm/h is reached with high crystalline quality of the grown material. The low temperature PL spectra show the free A-exciton line at 3.483 eV and rather narrow I2 lines with FWHM of 1–2 meV indicating high crystalline quality and low doping concentration. This HVPE-GaN has the potential to provide lattice-matched and thermally-matched substrates for further epitaxial growth of high quality GaN with a low dislocation density for advanced heterostructure devices.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-46338 (URN)10.1002/pssa.200303342 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
3. Free-standing HVPE-GaN Layers
Open this publication in new window or tab >>Free-standing HVPE-GaN Layers
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2003 (English)In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 0, no 7, 1985-1988 p.Article in journal (Refereed) Published
Abstract [en]

We have grown GaN layers with a thickness up to 340 μm in an rf-heated vertical HVPE reactor with a bottom-fed design. The GaN layers were separated from the sapphire substrate by a LLO process. The free-standing GaN was investigated by HRXRD, AFM and low temperature CL. The FWHM values of the ω-scans are 96 and 129 arcsec for the (104) and (002) reflection, respectively, which indicates high crystalline quality. The c and a lattice parameters are determined as c = 0.51850 ± 0.00004 nm and a = 0.31890 ± 0.00004 nm, indicating stress free material. The etch pit density was estimated to be 1 × 107 cm−2. The used HVPE growth procedure together with the subsequent LLO are obviously capable to provide high-quality free-standing GaN material for further epitaxial overgrowth.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-85826 (URN)10.1002/pssc.200303333 (DOI)
Available from: 2012-11-29 Created: 2012-11-29 Last updated: 2017-12-07
4. Characterization of high-quality free-standing GaN grown by HVPE
Open this publication in new window or tab >>Characterization of high-quality free-standing GaN grown by HVPE
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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.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-48267 (URN)10.1088/0031-8949/2004/T114/004 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
5. Characterization of crack-free relaxed GaN grown on 2″ sapphire
Open this publication in new window or tab >>Characterization of crack-free relaxed GaN grown on 2″ sapphire
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2005 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 98, no 7, 73525- p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate the growth of high-quality and virtually strain-free bulklike GaN by hydride vapor-phase epitaxy in a vertical atmospheric-pressure reactor with a bottom-fed design. The 300‐μm-thick GaN layer was grown on a 2″ (0 0 0 1) sapphire substrate buffered with a ∼ 2‐μm-thick GaN layer grown by metal-organic chemical-vapor deposition. During the cool down process to room temperature, cracking was induced in the sapphire substrate, thereby allowing the bulklike GaN layer to relax without provoking cracking of itself. The crystalline quality and the residual strain in the 2″ GaN wafer were investigated by various characterization techniques. The lateral homogeneity of the wafer was monitored by low-temperature photoluminescence mapping. High-resolution x-ray diffraction and photoluminescence measurements proved the high crystalline quality of the material grown. The position of the main near-band-gap photoluminescence line and the phonon spectra obtained from infrared spectroscopic ellipsometry show consistently that the 2″ crack-free GaN is virtually strain-free over a diameter of approximately 4 cm.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-30711 (URN)10.1063/1.2064311 (DOI)16323 (Local ID)16323 (Archive number)16323 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
6. Strain-free bulk-like GaN grown by hydride-vapor-phase-epitaxy on two-step epitaxial lateral overgrown GaN template
Open this publication in new window or tab >>Strain-free bulk-like GaN grown by hydride-vapor-phase-epitaxy on two-step epitaxial lateral overgrown GaN template
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2004 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 96, no 1, 799-806 p.Article in journal (Refereed) Published
Abstract [en]

Crack-free bulk-like GaN with high crystalline quality has been obtained by hydride-vapor-phase-epitaxy (HVPE) growth on a two-step epitaxial lateral overgrown GaN template on sapphire. During the cooling down stage, the as-grown 270-μm-thick GaN layer was self-separated from the sapphire substrate. Plan-view transmission electron microscopy images show the dislocation density of the free-standing HVPE-GaN to be ∼2.5×107 cm−2 on the Ga-polar face. A low Ga vacancy related defect concentration of about 8×1015 cm−3 is extracted from positron annihilation spectroscopy data. The residual stress and the crystalline quality of the material are studied by two complementary techniques. Low-temperature photoluminescence spectra show the main neutral donor bound exciton line to be composed of a doublet structure at 3.4715 (3.4712) eV and 3.4721 (3.4718) eV for the Ga- (N-) polar face with the higher-energy component dominating. These line positions suggest virtually strain-free material on both surfaces with high crystalline quality as indicated by the small full width at half maximum values of the donor bound exciton lines. The E1(TO) phonon mode position measured at 558.52 cm−1 (Ga face) by infrared spectroscopic ellipsometry confirms the small residual stress in the material, which is hence well suited to act as a lattice-constant and thermal-expansion-coefficient matched substrate for further homoepitaxy, as needed for high-quality III-nitride device applications. © 2004 American Institute of Physics.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-24593 (URN)10.1063/1.1753073 (DOI)6769 (Local ID)6769 (Archive number)6769 (OAI)
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2017-12-13
7. Positron annihilation study of HVPE grown thick GaN layers
Open this publication in new window or tab >>Positron annihilation study of HVPE grown thick GaN layers
2005 (English)In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 202, no 5, 713-717 p.Article in journal (Refereed) Published
Abstract [en]

Single-crystalline GaN layers with a thickness up to 330 µm were grown by hydride vapor phase epitaxy on basal plane sapphire at gallium stable conditions in a bottom-fed vertical reactor at atmospheric pressure. Positron annihilation spectroscopy experiments were implemented in order to identify native point defects in the as-grown non-intentionally doped n-type GaN. Comparatively low concentrations of Ga vacancy related defects in the order of 1016 to 1017 cm–3 were extracted from the positron annihilation spectroscopy data. The Ga vacancy defect concentration was related to the intensity of the yellow photoluminescence band centered at 2.2 eV. The influence of the growth rate on the Ga vacancy related defect concentration was investigated. A trend of decreasing of the defect concentration with increasing of layer thickness is observed, which correlates with improving crystalline quality with the thickness.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-46094 (URN)10.1002/pssa.200461420 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-05-11
8. Micro-Raman scattering profiling studies on HVPE-grown free-standing GaN
Open this publication in new window or tab >>Micro-Raman scattering profiling studies on HVPE-grown free-standing GaN
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2004 (English)In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 201, no 12, 2773-2776 p.Article in journal (Refereed) Published
Abstract [en]

Free-standing GaN of ∼330 μm thickness with low defect density was prepared by hydride vapor-phase epitaxy (HVPE) on sapphire in a vertical atmospheric-pressure reactor and a subsequent laser-induced lift-off process. The structural and optical properties of the material were assessed by various characterization techniques, like X-ray diffraction, photo- and cathodoluminescence, spectroscopic ellipsometry, positron annihilation spectroscopy, and transmission electron microscopy. Here, we focus on μ-Raman scattering profiling studies providing the vertical strain distribution and the evolution of the crystalline quality with increasing layer thickness. Profiles of the free-carrier concentration are obtained from monitoring the LO-phonon plasmon coupled mode. Comparative investigations are performed on the material before and after separation of the sapphire substrate. The GaN material presented here is well capable of serving as a substrate for further homoepitaxial strain-relaxed and crack-free growth needed for fabrication of high-quality III-nitride device heterostructures.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-46173 (URN)10.1002/pssa.200405013 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13

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