liu.seSearch for publications in DiVA
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Growth and Characterization of AlN: From Nano Structures to Bulk Material
Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Aluminum nitride (AlN) exhibits a large direct band gap, 6.2 eV, and is thus suitable forsolid state white-light-emitting devices. It is capable in spintronics because of its high Curietemperature if doped with transition metals. AlN can also be used as a buffer layer for growth ofdevice-grade GaN as well as for application in sensors, surface acoustic wave devices, and hightemperatureelectronics. AlN shows excellent field-emission performance in vacuummicroelectronic devices due to its small electron affinity value, which is from negative to 0.6 eV.In this sense, nanostructured AlN, such as AlN nanowires and nanorods, is important forextending our knowledge on the potential of nanodevice applications. For growth of bulk AlN thesublimation- recondensation (a kind of physical vapor transport growth) method is the mostsuccessful and promising crystal growth technique.

In thesis the physical vapor transport (PVT) principle has been implemented for synthesisof AlN on 4H-SiC in sublimation epitaxy close space configuration. It has been shown that theAlN crystal morphology is responsive to the growth conditions given by temperature (1650-1900oC) and nitrogen pressure (200-800 mbar) and each morphology kind (platelet-like, needles, columnar structure, continuous layers, and free-standing quasi bulk material) occurs within anarrow window of growth parameters. Controlled operation conditions for PVT growth of wellaligned perfectly oriented arrays of AlN highly symmetric hexagonal microrods have beenelaborated and the mechanism of microrod formation has been elucidated. Special patterned SiCsubstrates have been created which act as templates for the AlN selective area growth. Themicrorods revealed an excellent feature of boundary free coalescence with growth time,eventually forming ~120 μm thick AlN layer which can be easily detached from the SiC substratedue to a remarkable performance of structural evolution. It was discovered that the locally grownAlN microrods emerge from sharp tipped hexagonal pyramids, which consist of the rare 2H-SiCpolytype and a thin AlN layer on the surface. Two unique consequences appear from the finding,the first is that the 2H-SiC polytype facilitates the nucleation of wurtzite AlN, and the second isthat the bond between the low angle apex of the pyramids and the AlN layer is very week, thusallowing an easy separation to yield free standing wafers. AlN nanowires with an aspect ratioas high as 600 have been grown with a high growth rate. Again, they have perfect alignmentalong the c-axis of the wurtzite structure with small tilt given by the orientation of the SiCsubstrate. The nanowires possess a single crystal structure with high perfection, since neitherdislocations nor stacking faults were revealed.

The proposed growth concept can be further explored to enlarge the free standing AlNwafers up to a size provided by commercially available SiC four inch wafers. Also, AlN wafersfabricated by the present method may be used as seeds for large boule growth. AlN nanowires, asobtained in this study, can be used for creating a piezoelectric generator and field emitters withhigh efficiency.

Abstract [sv]

Aluminium nitrid (AlN) har ett stort direkt bandgap (6.2 eV) och är lämplig för lysdioder.Det är tillämpligt inom spinnelektronik eftersom det har en hög Marie Curie-temperatur när det ärdopad med övergångsmetaller. AlN kan även användas som ett buffertskikt för tillväxt avkomponentkvalitativt GaN likväl som för sensortillämpningar, ytvågsfilterkomponenter, ochhögtemperaturelektronik. Aluminium nitrid visar excellent fältemission i vakuumkomponenter pågrund av sin låga elektronaffinitet, som är från negativt till 0.6 eV. I det här fallet så ärnanostrukturer av AlN, som nanotrådar och -stavar, viktiga för att utöka vår kunskap ompotentiella nanokomponenter. För tillväxt av AlN är sublimeringsmetoden den mestframgångsrika och lovande framställningstekniken av kristaller.

I den här avhandlingen så har principen för den fysiska gastransporttekniken (PVT)implementerats för syntes av AlN på 4H-SiC filmer i en ny konfiguration genomsublimeringsepitaxi. Det demonstreras att morfologin hos AlN visar respons förtillväxtförhållandena som ges av temperatur (1650-1900oC) och kvävetryck (200-800 mbar) ocholika morfologityper (skivlika, trådar, kolumnstrukturer, kontinuerliga skikt, och friståendekvasibulkmaterial)uppstår inom ett snävt fönster av tillväxtparametrar. Kontrollerade operativaförhållanden för PVT-tillväxt av räta perfekt orienterade ansamlingar av symmetriska AlNmikrostavar har utvecklats och deras formationsmekanism diskuterats. Speciellt mönstrade SiCsubstrat har skapats som agerar utgångsmaterial för selektiv AlN tillväxt. Mikrostavarna avslöjarett särdrag av sammanväxning utan gränslinjer med tillväxttid, som formar 120 μm tjocka AlNskikt som lätt kan avskiljas från SiC substratet genom en anmärkningsvärd strukturell evolution.Upptäckten gjordes att lokal tillväxt av AlN mikrostavar uppkommer från skarpa hexagonalapyramider som består av den sällan förekommande 2H-SiC modifikationen och tunna AlN skiktpå ytan. Två unika följder uppkommer genom upptäckten, den första att 2H-SiC modifikationenfrämjar bildning av wurtzite AlN, och den andra att bindningen mellan spetsen av pyramiden ochAlN skiktet är väldigt svag, vilket medger en enkel separering för att erhålla fristående wafers.

AlN nanotrådar med ett aspektförhållande så stort som 600 har blivit framställda med högframställningshastighet. Återigen, de har perfekt linjering längs c-axeln av wurtzite-strukturenmed en låg vinkling som ges av orienteringen av SiC substratet. Nanotrådarna har en perfektkristallstruktur eftersom varken dislokationer eller stackningsfel kunde observeras.

Det föreslagna framställningskonceptet kan vidare utforskas för att utöka fristående AlNwafers upp till en storlek som ges av kommersiellt tillgängliga SiC fyratumssubstrat. Vidare såkan AlN wafers som framställs genom metoden användas som utgångsmaterial för kristaller förframställning av stora götar. AlN nanotrådar, som utvecklats i denna studie, kan användas för attskapa piezoelektriska generatorer och fältemissionskomponenter med hög effektivitet.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2008. , 87 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1200
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-14814ISBN: 978-91-7393-839-6 (print)OAI: oai:DiVA.org:liu-14814DiVA: diva2:25302
Public defence
2008-08-20, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2008-09-24 Created: 2008-09-24 Last updated: 2009-09-04Bibliographically approved
List of papers
1. Sublimation growth of AlN crystals: Growth mode and structure evolution
Open this publication in new window or tab >>Sublimation growth of AlN crystals: Growth mode and structure evolution
Show others...
2005 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 281, no 1, 81-86 p.Article in journal (Refereed) Published
Abstract [en]

The aim of this study has been to realize growth conditions suitable for seeded sublimation growth of AlN and to understand the relationship between external growth parameters and the initial stages of growth with respect to growth mode and structure evolution. Close space sublimation growth geometry has been used in a RF-heated furnace employing high-purity graphite coated by TaC with a possibility to change the growth environment from C- to Ta-rich. Influence of certain impurities on the initially formed crystallites with respect to their shape, size and population has been considered. It is shown that some impurity containing vapor molecules may act as transport agents and suppliers of nitrogen for the AlN growth. SiC seeds, both bare and with MOCVD AlN buffer, have been employed. By varying the process conditions we have grown crystals with different habits, e.g. from needles, columnar- and plate-like, to freestanding quasi-bulk material. The growth temperature ranged 1600–2000 °C whereas the optimal external nitrogen pressure varied from 200 to 700 mbar. There is a narrow parameter window in the relationship temperature–pressure for the evolution of different structural forms. Growth modes with respect to process conditions are discussed.

Keyword
A1. Crystal morphology and structure, A2. Growth from vapor, A3. Sublimation epitaxy, B1. Aluminium nitride
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:liu:diva-14801 (URN)10.1016/j.jcrysgro.2005.03.015 (DOI)
Available from: 2008-09-24 Created: 2008-09-24 Last updated: 2017-12-13
2. Fast epitaxy by PVT of SiC in hydrogen atmosphere
Open this publication in new window or tab >>Fast epitaxy by PVT of SiC in hydrogen atmosphere
2005 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 275, no 1-2, e1103-e1107 p.Article in journal (Refereed) Published
Abstract [en]

Epitaxial growth in hydrogen atmosphere has been studied in relation to sublimation epitaxial growth. A new type of features with a hexagonal shape are observed in the layers grown in hydrogen atmosphere. The morphological details of the features have been studied with optical microscopy and atomic force microscopy. An interactive relation of the defect appearance with the step flow growth mode seems to be present. The results are compared with growth in vacuum, argon, and helium conditions. The possible influence of thermal component to a reactive one in hydrogen etching is discussed.

Keyword
A1. Defects, A1. Nucleation, A3. Physical vapor deposition processes
National Category
Other Basic Medicine
Identifiers
urn:nbn:se:liu:diva-14802 (URN)10.1016/j.jcrysgro.2004.11.129 (DOI)
Available from: 2008-09-24 Created: 2008-09-24 Last updated: 2017-12-13
3. Growth and morphology of AlN crystals
Open this publication in new window or tab >>Growth and morphology of AlN crystals
2006 (English)In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T126, 127-130 p.Article in journal (Refereed) Published
Abstract [en]

This study focused on growth dependencies, morphological forms and initial nucleation of aluminium nitride (AlN) crystals. Epitaxial layers of AlN have been grown on 4H-SiC substrates by sublimation recondensation in a radio frequency (RF) heated graphite furnace. Both AlN nuclei size and growth rate increased as temperature was increased and decreased as the pressure was increased. The results of these effects are different kinds of surface morphology. We have observed three modes of AlN single crystals: plate-like, columnar and needle-like. Optical microscopy and scanning electron microscopy (SEM) along with atomic force microscopy (AFM) were used to characterize the crystal surface morphology. Cathodoluminescence (CL) and x-ray diffraction (XRD) were applied to determine crystal quality and crystallographic orientation of the grown crystals.

National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-14803 (URN)10.1088/0031-8949/2006/T126/028 (DOI)
Available from: 2008-09-24 Created: 2008-09-24 Last updated: 2017-12-13
4. Aligned AlN nanowires and microrods by self-patterning
Open this publication in new window or tab >>Aligned AlN nanowires and microrods by self-patterning
2007 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 90, no 12, 123103- p.Article in journal (Refereed) Published
Abstract [en]

Self-patterned AlN microrods and nanowires were grown on 4H-SiC substrate by a physical vapor transport method. AlN hexagonal pyramids were found to be nucleation sites for the evolution of the observed morphological forms. The average diameter and length of the nanowires are about 200  nm and 90  µm, respectively. The density of microrods corresponds to the concentration of the pyramids, while the nanowires are less compact. Low-temperature cathodoluminescence spectra of microrods show band gap emission of AlN at 208  nm, which confirms that they are AlN single crystals. A formation mechanism of the AlN structures is suggested.

National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-14805 (URN)10.1063/1.2715129 (DOI)
Available from: 2008-09-24 Created: 2008-09-24 Last updated: 2017-12-13
5. Formation of needle-like and columnar structures of AlN
Open this publication in new window or tab >>Formation of needle-like and columnar structures of AlN
2007 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 300, no 1, 130-135 p.Article in journal (Refereed) Published
Abstract [en]

The present study focused on understanding the formation of needle-like and columnar structures by investigating the initial nucleation of aluminium nitride (AlN) on SiC substrates with SEM, AFM, and XRD. The grown AlN consisted of high concentration (8×104 cm−2) hexagonal hillocks (HHs) that originate from threading dislocations in the substrate. The KOH etching technique has been used to examine the origin and formation process of HHs and defect reduction in the grown AlN crystals. A model is introduced to explain the AlN HH formation. The SEM result shows that the AlN columnar structure was formed by merging of needles, which are grown exactly on completed AlN HHs, followed by a lateral growth.

Keyword
A1. Nucleation; A2. Growth from vapor; A2. Single crystal growth; B1. Nitride; B2. Semiconducting III–V material
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-14806 (URN)10.1016/j.jcrysgro.2006.11.005 (DOI)
Available from: 2008-09-24 Created: 2008-09-24 Last updated: 2017-12-13
6. Fabrication of free-standing AlN crystals by controlled microrod growth
Open this publication in new window or tab >>Fabrication of free-standing AlN crystals by controlled microrod growth
2008 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 300, no 5, 935-939 p.Article in journal (Refereed) Published
Abstract [en]

The aim of this study was to propose a growth procedure for preparation of crack-free thick aluminum nitride (AlN) layers that can be easily separated from the substrate. The overall process is based on the physical vapor transport method employing a seed and a source material. In this case, the substrate is an epitaxial 4H-SiC layer and the growth of AlN is initiated at etch pits formed during the ramp up time prior to establishing growth temperature. Development of hexagonal pyramids on which arrays of microrods are formed is the core of the growth procedure. Free-standing wafers having 10 mm diameter and about 120 μm thick have been fabricated.

Keyword
A1. X-ray topography; A2. Growth from vapor; A2. Single-crystal growth; B2. Semiconducting III–V materials
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-14807 (URN)10.1016/j.jcrysgro.2007.11.124 (DOI)
Available from: 2008-09-24 Created: 2008-09-24 Last updated: 2017-12-13
7. Employing discontinuous and continuous growth modes for preparation of AlN nanostructures on SiC substrates
Open this publication in new window or tab >>Employing discontinuous and continuous growth modes for preparation of AlN nanostructures on SiC substrates
2007 (English)In: ECSCRM 2006, Newcastle, UK: Materials Science Forum Vols. 556-557, Trans Tech Publications, Switzerland , 2007, Vol. 556-557, 1031-1034 p.Conference paper, Published paper (Refereed)
Abstract [en]

In this report we present results on growth and characterization of AlN wires and thinfilms on SiC substrates. We have employed PVT technique in close space geometry for AlNdeposition on SiC off oriented substrates, most of which were prepared to have scratch-free smoothas-grown surface by SiC sublimation epitaxy. By manipulating the surface kinetics we have beenable to determine growth conditions yielding discontinuous or continuous morphologiescorresponding to nanowires and thin films, respectively. A particular feature of the latterexperiments is the fast temperature ramp up at the growth initiation. The AlN surface morphologywas characterized by optical, AFM and XRD tools, which showed good crystal quality independentof the growth mode.

Place, publisher, year, edition, pages
Trans Tech Publications, Switzerland, 2007
Keyword
AlN, Nanowires, Thin films, PVT, Structural
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-14808 (URN)10.4028/www.scientific.net/MSF.556-557.1031 (DOI)
Available from: 2008-09-24 Created: 2008-09-24 Last updated: 2009-05-19
8. Freestanding AlN single crystals enabled by self-organization of 2H-SiC pyramids on 4H-SiC substrates
Open this publication in new window or tab >>Freestanding AlN single crystals enabled by self-organization of 2H-SiC pyramids on 4H-SiC substrates
Show others...
2009 (English)In: APPLIED PHYSICS LETTERS, ISSN 0003-6951, Vol. 94, no 8, 082109- p.Article in journal (Refereed) Published
Abstract [en]

A sublimation-recondensation process is presented for high quality AlN (0001) crystals at a high growth rate by employing 4H-SiC substrates with a predeposited epilayer. It is based on the coalescence of well oriented AlN microrods, which evolve from the apex of 2H-SiC pyramids grown out of hexagonal pits formed by thermal etching of the substrate during a temperature ramp up. This process yields stress-free 120-mu m-thick AlN single crystals with a dislocation density as low as 2x10(6) cm(-2).

Keyword
aluminium compounds, condensation, crystal growth from vapour, dislocation density, etching, III-V semiconductors, semiconductor growth, silicon compounds, sublimation, wide band gap semiconductors
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-17388 (URN)10.1063/1.3085958 (DOI)
Available from: 2009-03-21 Created: 2009-03-21 Last updated: 2016-08-31
9. Defect-free Single Crystal AlN Nanowires by Physical Vapor Transport Growth
Open this publication in new window or tab >>Defect-free Single Crystal AlN Nanowires by Physical Vapor Transport Growth
Show others...
(English)Manuscript (Other academic)
Abstract [en]

Growth by vapor-solid mechanism of AlN nanowires with a diameter in the range of 40-500nm and a length reaching 100 μm, resulting in a max aspect ratio of 600, is reported. Theobjects are obtained at 1750 oC and 850 mbar nitrogen pressure on 4H-SiC patternedsubstrates by sublimation epitaxy, which is a version of the physical vapor transport techniqueand provides a high growth rate. The nanowires are hexagonally shaped and perfectly alignedalong the 0001 direction with a small tilt given by the substrate vicinality. It is observed thatunder nitrogen excess a preferential growth along the c-axis of the wurtzite structure takesplace, and switches to lateral growth below some critical value of nitrogen pressure.Investigations by SEM, TEM, CL and Raman spectroscopy measurements were carried out. Itis shown that the nanowires consist of wurtzitic AlN with defect free crystal structure.Possible applications have been depicted.

National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-14812 (URN)
Available from: 2008-09-24 Created: 2008-09-24 Last updated: 2016-08-31

Open Access in DiVA

fulltext(923 kB)2397 downloads
File information
File name FULLTEXT01.pdfFile size 923 kBChecksum SHA-512
c278a28d93577c804b424c652c89b82701add37c002ed4f0e0948e3e9c5fbb13d6451750fc64fc41d0fb9612091bb6d9f9b87f000af419ee9c8f38fc2a65625c
Type fulltextMimetype application/pdf
cover(3123 kB)234 downloads
File information
File name COVER01.pdfFile size 3123 kBChecksum SHA-512
30be0df724f2084e016589fe5aa385e2e73d598f6025c9f83c5d2d50f1c47e54b92d8763db43a1684aa77b6e10e588f912b635d5816d2c36c6afec5f2a9c2aa7
Type coverMimetype application/pdf

Authority records BETA

Yazdi, Gholamreza

Search in DiVA

By author/editor
Yazdi, Gholamreza
By organisation
Materials Science The Institute of Technology
Physical Sciences

Search outside of DiVA

GoogleGoogle Scholar
Total: 2397 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 2035 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf