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Sublimation Growth of 3C-SiC: From Thick Layers to Bulk Material
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Silicon carbide (SiC) is a semiconductor material which holds high promises for various device applications. It can be obtained in different crystal structures called polytypes. The most common ones are hexagonal (6H- and 4H-SiC) and cubic (3C-SiC) silicon carbide. The 6H- and 4H-SiC single crystal substrates are commercially available, while technologies for the growth of 3C-SiC are still under development. The unique 3C-SiC properties like isotropy, narrower bandgap (2.4 eV)  compared to hexagonal polytypes (about 3 eV) and high electron mobility make it better over hexagonal counterparts for some semiconductor applications, for example, metal oxide semiconductor field effect transistors (MOSFETs). However, due to lack of high quality material, the full potential of 3C-SiC in device applications has not been revealed. In addition, it has properties suitable to explore new concepts in efficient photovoltaics or solar driven hydrogen generation by water splitting.

There is a need for 3C-SiC seeds to grow large 3C-SiC crystals by the widely used Physical Vapor Transport (PVT) technique. In case of hexagonal SiC polytypes such seeds were produced by the Lely method during which hexagonal SiC crystals spontaneously nucleate on the inner walls of a crucible. However, the formation of 3C-SiC using the Lely method is rarely observed. Therefore, the 3C-SiC has to be heteroepitaxially grown on silicon or hexagonal SiC substrates. Silicon is an inexpensive material with very high crystalline quality. However, due to almost 20% mismatch in lattice parameters and 8% difference in thermal expansion coefficient there is a high density of structural defects formed at the 3C-SiC/Si interface. In contrast, the 3C-SiC/hexagonal SiC material system does not encounter such problems, but there are other challenges like polytype stability or formation of structural defects called double positioning boundaries (DPBs).

This thesis work mainly focuses on the growth of 3C-SiC on hexagonal SiC substrates using sublimation epitaxy. The research covers the development of growth process for thick (~1 mm) 3C-SiC layers, advancement of the growth process to eliminate DPBs and growth of bulk material using thick 3C-SiC layers as seeds. The 3C-SiC was grown on off-oriented hexagonal SiC substrates. The surfaces of such substrates contain high density of steps. Therefore, they have mostly been used for the growth of homoepitaxial hexagonal layers or bulk crystals via step flow mechanism. However, as demonstrated in this thesis, under special conditions the 3C-SiC with high crystalline quality can also be grown on off-oriented hexagonal substrates. The stability window for the growth of hexagonal and cubic polytypes on nominally on-axis hexagonal SiC substrates is also explored. Moreover, it is demonstrated how the temperature profile inside the graphite crucible is influenced by the change in thermal insulation properties and how such change results in enhanced polytype stability during the growth of thick SiC layers. In addition, different sources for sublimation epitaxial growth of doped SiC layers were analyzed to gain further understanding of new parameter windows.

As a part of this thesis, a sublimation etching of 6H-, 4H- and 3C-SiC polytypes is presented using two different etching arrangements in vacuum (10-5 mbar) and Ar ambient. It is demonstrated that this technique can be used to remove residual scratches on the surface as well as to obtain various surface step structures which could be used for the growth of graphene nanostructures.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2016. , 45 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1760
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-127802ISBN: 978-91-7685-778-6 (print)OAI: oai:DiVA.org:liu-127802DiVA: diva2:927799
Public defence
2016-06-09, Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2016-05-13 Created: 2016-05-13 Last updated: 2016-11-23Bibliographically approved
List of papers
1. Lateral Enlargement Growth Mechanism of 3C-SiC on Off-Oriented 4H-SiC Substrates
Open this publication in new window or tab >>Lateral Enlargement Growth Mechanism of 3C-SiC on Off-Oriented 4H-SiC Substrates
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2014 (English)In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 14, no 12, 6514-6520 p.Article in journal (Refereed) Published
Abstract [en]

We introduce a 3C-SiC growth concept on off-oriented 4H-SiC substrates using a sublimation epitaxial method. A growth model of 3C-SiC layer development via a controlled cubic polytype nucleation on in situ formed on-axis area followed by a lateral enlargement of 3C-SiC domains along the step-flow direction is outlined. Growth process stability and reproducibility of high crystalline quality material are demonstrated in a series of 3C-SiC samples with a thickness of about 1 mm. The average values of full width at half-maximum of ω rocking curves on these samples vary from 34 to 48 arcsec indicating high crystalline quality compared to values found in the literature. The low temperature photoluminescence measurements also confirm a high crystalline quality of 3C-SiC and indicate that the residual nitrogen concentration is about 1–2 × 1016 cm–3. Such a 3C-SiC growth concept may be applied to produce substrates for homoepitaxial 3C-SiC growth or seeds which could be explored in bulk growth of 3C-SiC.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2014
National Category
Physical Sciences Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-112510 (URN)10.1021/cg501424e (DOI)000345884000043 ()
Available from: 2014-11-29 Created: 2014-11-29 Last updated: 2016-05-13Bibliographically approved
2. Single Domain 3C-SiC Growth on Off-Oriented 4H-SiC Substrates
Open this publication in new window or tab >>Single Domain 3C-SiC Growth on Off-Oriented 4H-SiC Substrates
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2015 (English)In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 15, no 6, 2940-2947 p.Article in journal (Refereed) Published
Abstract [en]

We investigated the formation of structural defects in thick (∼1 mm) cubic silicon carbide (3C-SiC) layers grown on off-oriented 4H-SiC substrates via a lateral enlargement mechanism using different growth conditions. A two-step growth process based on this technique was developed, which provides a trade-off between the growth rate and the number of defects in the 3C-SiC layers. Moreover, we demonstrated that the two-step growth process combined with a geometrically controlled lateral enlargement mechanism allows the formation of a single 3C-SiC domain which enlarges and completely covers the substrate surface. High crystalline quality of the grown 3C-SiC layers is confirmed using high resolution X-ray diffraction and low temperature photoluminescence measurements.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2015
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-118525 (URN)10.1021/acs.cgd.5b00368 (DOI)000355890400051 ()
Note

Swedish Energy Agency; Swedish Research Council; Swedish Governmental Agency for Innovation Systems (Vinnova)

Available from: 2015-05-29 Created: 2015-05-29 Last updated: 2016-05-13
3. Growth optimization and applicability of thick on-axis SiC layers using sublimation epitaxy in vacuum
Open this publication in new window or tab >>Growth optimization and applicability of thick on-axis SiC layers using sublimation epitaxy in vacuum
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2016 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 448, 51-57 p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate growth of thick SiC layers (100–200 µm) on nominally on-axis hexagonal substrates using sublimation epitaxy in vacuum (10−5 mbar) at temperatures varying from 1700 to 1975 °C with growth rates up to 270 µm/h and 70 µm/h for 6H- and 4H–SiC, respectively. The stability of hexagonal polytypes are related to process growth parameters and temperature profile which can be engineered using different thermal insulation materials and adjustment of the induction coil position with respect to the graphite crucible. We show that there exists a range of growth rates for which single-hexagonal polytype free of foreign polytype inclusions can be maintained. Further on, foreign polytypes like 3C–SiC can be stabilized by moving out of the process window. The applicability of on-axis growth is demonstrated by growing a 200 µm thick homoepitaxial 6H–SiC layer co-doped with nitrogen and boron in a range of 1018 cm−3 at a growth rate of about 270 µm/h. Such layers are of interest as a near UV to visible light converters in a monolithic white light emitting diode concept, where subsequent nitride-stack growth benefits from the on-axis orientation of the SiC layer.

Keyword
Mass transfer;Substrates;Single crystal growth;Semiconducting materials
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-128610 (URN)10.1016/j.jcrysgro.2016.05.017 (DOI)
Available from: 2016-05-25 Created: 2016-05-25 Last updated: 2016-11-23
4. Surface engineering of SiC via sublimation etching
Open this publication in new window or tab >>Surface engineering of SiC via sublimation etching
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2016 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 390, 816-822 p.Article in journal (Refereed) Published
Abstract [en]

We present a technique for etching of SiC which is based on sublimation and can be used to modify the morphology and reconstruction of silicon carbide surface for subsequent epitaxial growth of various materials, for example graphene. The sublimation etching of 6H-, 4H- and 3C-SiC was explored in vacuum (10−5 mbar) and Ar (700 mbar) ambient using two different etching arrangements which can be considered as Si-C and Si-C-Ta chemical systems exhibiting different vapor phase stoichiometry at a given temperature. The surfaces of different polytypes etched under similar conditions are compared and the etching mechanism is discussed with an emphasis on the role of tantalum as a carbon getter. To demonstrate applicability of such etching process graphene nanoribbons were grown on a 4H-SiC surface that was pre-patterned using the thermal etching technique presented in this study.

Place, publisher, year, edition, pages
Amsterdam: Elsevier, 2016
National Category
Natural Sciences Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-131817 (URN)10.1016/j.apsusc.2016.08.149 (DOI)000385900700098 ()
Note

Funding agencies: Swedish Research Council [621-2014-5825]; Graphene Flagship [CNECT-ICT-604391]; AForsk foundation [16-576]; Swedish Foundation for Strategic Research (SSF); Knut and Allice Wallenberg Foundation

Available from: 2016-10-08 Created: 2016-10-08 Last updated: 2016-11-23Bibliographically approved
5. Effects of source material on epitaxial growth of fluorescent SiC
Open this publication in new window or tab >>Effects of source material on epitaxial growth of fluorescent SiC
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2012 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 522, 7-10 p.Article in journal (Refereed) Published
Abstract [en]

The growth of fluorescent SiC using Fast Sublimation Growth Process was demonstrated using different types of SiC source materials. These were prepared by (i) high-temperature hot pressing, (ii) chemical vapor deposition and (iii) physical vapor transport. The optimized growth rates of 50 μm/h, 170 μm/h and 200 μm/h were achieved using the three types of sources, respectively. The best results in respect to growth rates are obtained using higher density sources. Fluorescent SiC layers with mirror-like morphology, very good crystal quality and yellowish or warm white light photoluminescence at room temperature were grown using all three types of the source materials.

Place, publisher, year, edition, pages
Elsevier, 2012
Keyword
Sublimation growth; Fluorescence; Photoluminescence; Silicon carbide
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-73709 (URN)10.1016/j.tsf.2011.10.176 (DOI)000310782000003 ()
Available from: 2012-01-11 Created: 2012-01-11 Last updated: 2016-05-13

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