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Sublimation Growth and Performance of Cubic Silicon Carbide
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Silicon carbide (SiC) is a wide band gap semiconductor satisfying requirements to replace silicon in devices operating at high power and high frequency at high temperature, and in harsh environments. Hexagonal polytypes of SiC, such as 6H-SiC and 4H-SiC are available on the power device markets. However, the cubic SiC (3C-SiC) polytype is still not industrially used, essentially due to the lack of 3CSiC substrates. This is mainly because of a high density of defects appearing in the  crystals. Thus, it is critical to understand material growth and defect formation, and learn to control their appearance. Ensuring, that growth methods capable of large scale industrial production can be applied.

The aim of this work was to develop operation conditions for fabrication of 3C-SiC crystals via understanding fundamentals of the growth process and to explore structural and electrical properties of the grown material, including its suitability for substrate applications. The physical vapor transport or sublimation process has already shown a capability to produce substantial quantities of large area and high quality hexagonal SiC substrates. In the present study a similar growth principle, but in a different geometry, namely sublimation epitaxy, was applied. Using this method very high growth rates (up to 1 mm/h) can be achieved for hexagonal polytypes while maintaining high material quality. Additionally, the growth process does not require expensive or hazardous materials, thus making the method very attractive for industrial use.

When growing 3C-SiC directly on 6H-SiC, the substrate roughness does not have significant influence on the yield and quality of 3C-SiC. This is mostly due to the growth of homoepitaxial 6H-SiC which appears before the 3C-SiC. Structural characterization showed that 3C-SiC grown directly on 6HSiC exhibited the highest quality as compared with other substrate preparation, such as annealing or deposition of a 3C-SiC buffer layer. Thus, further investigation was devoted to the growth of 3C-SiC on 6H-SiC substrates.

The parameter window for the growth of 3C-SiC is quite narrow. The temperature interval is from ~1675oC, where the material starts to nucleate, to ~1850oC, where an uncontrolled growth process begins. Si-rich conditions (high Si/C ratio) and high supersaturation are needed in the growth chamber for preferable 3C-SiC nucleation. Deviation from these parameters leads to the growth of homoepitaxial 6HSiC in spiral or 2D island mode along with cubic SiC with high defect density.

Nucleation is the most important step in the growth process. The growth on 6H-SiC substrates commences from homoepitaxial 6H-SiC growth in spiral mode, which makes the surface perfect for 3CSiC nucleation. At temperature of ~1675oC the supersaturation is high enough and the 3C-SiC nucleation initiates in two-dimensional islands on the 6H-SiC spiral terraces. Control of the homoepitaxial 6H-SiC growth is a key element in the growth of 3C-SiC.

SiC is a polar material having surfaces terminated by either silicon or carbon atoms, called Si- and C-face, respectively. The growth is different on both faces due to the different free surface energies. The lower surface free energy on the C-face causes more uniform nucleation of 3C-SiC and thereafter more uniform twinned domain distribution. Additionally, calculations showed that increase of growth temperature from 1675oC to 1775oC does not change the supersaturation ratio on the C-face due to a much higher surface diffusion length. This results in appearance of pits in the 3C-SiC layer with a 6H-SiC spiral. The pits were not observed on Si-face material as the supersaturation ratio was much higher. Pits formed in the early stages of growth were overgrown more effectively during the later stages.

Characterization by transmission electron microscopy showed that transformation from 6H-SiC to 3C-SiC is not abrupt and can appear in two different modes. The first one is forming a few micrometers of polytypic transition zone consisting predominantly of 15R-, 6H- and 3C-SiC. The second one appears due to a competition between 3C-SiC and 6H-SiC resulting in a step-like intermixing zone between these polytypes. Four-fold twins were observed, which resulted in depressions at the surface of 3C-SiC. These defects expand proportionally to the layer thickness, thus drastically reducing usable area of thick layers.

Electrical measurements revealed carrier mobility ~200 cm2/Vs at room temperature and the dominant charge carrier scattering is by neutral centers and phonons. The neutral centers originate from extended defects, such as 6H-SiC inclusions, stacking faults and twin boundaries. By growing 3C-SiC on atomically flat and vicinal substrates a preferential orientation of twin boundaries (TBs) was achieved. The mobility was higher in the material with twin boundaries parallel to the current flow, and lower when twin boundaries were perpendicular to the current flow. This was less pronounced at higher temperature as relatively fewer carriers have to overcome barriers created by TBs.

Finally, the substrate capability of the 3C-SiC (111) was demonstrated by growth of a monolayer graphene, which was compared with graphene grown on hexagonal SiC poytypes. The quality of the graphene in terms of thickness uniformity and pit appearance was the best when grown on 3C-SiC. The lower quality on hexagonal substrates was attributed to a more difficult process control which is due to the more complex crystal structure.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. , 68 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1435
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-76371ISBN: 978-91-7519-935-1 (print)OAI: oai:DiVA.org:liu-76371DiVA: diva2:514133
Public defence
2012-05-03, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2012-04-05 Created: 2012-04-05 Last updated: 2012-04-06Bibliographically approved
List of papers
1. Effect of initial substrate conditions on growth of cubic silicon carbide
Open this publication in new window or tab >>Effect of initial substrate conditions on growth of cubic silicon carbide
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2011 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 324, no 1, 7-14 p.Article in journal (Refereed) Published
Abstract [en]

In order to analyze the epitaxial growth of cubic silicon carbide by sublimation epitaxy on different substrates, four different 6H-SiC substrate preparations were used: (i) as-received, (ii) re-polished, (iii) annealed and covered by silicon layer and (iv) with (1 1 1) 3C-SiC buffer layer. Almost 100% coverage and low twin density was achieved when grown on the buffer layer. The XRD and TEM characterizations show better material quality when the layer is grown directly on 6H-SiC substrates. Background doping evaluated by LTPL is in the range of 10(16) cm(-3) for N and 10(16) cm(-3) for Al in all grown layers.

Place, publisher, year, edition, pages
Elsevier Science B.V., Amsterdam., 2011
Keyword
Nucleation; Characterization; Substrates; Vapor phase epitaxy; Cubic silicon carbide
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-69870 (URN)10.1016/j.jcrysgro.2011.03.024 (DOI)000292362600002 ()
Note
Original Publication: Remigijus Vasiliauskas, M. Marinova, Mikael Syväjärvi, Rickard Liljedahl, G. Zoulis, J. Lorenzzi, G. Ferro, S. Juillaguet, J. Camassel, E. K. Polychroniadis and Rositsa Yakimova, Effect of initial substrate conditions on growth of cubic silicon carbide, 2011, Journal of Crystal Growth, (324), 1, 7-14. http://dx.doi.org/10.1016/j.jcrysgro.2011.03.024 Copyright: Elsevier http://www.elsevier.com/ Available from: 2011-08-09 Created: 2011-08-08 Last updated: 2017-12-08
2. Nucleation Control of Cubic Silicon Carbide on 6H- Substrates
Open this publication in new window or tab >>Nucleation Control of Cubic Silicon Carbide on 6H- Substrates
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2012 (English)In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 12, no 1, 197-204 p.Article in journal (Refereed) Published
Abstract [en]

The nucleation of cubic (3C) SiC on on-axis 6H-SiC was investigated in the temperature range 1500–1775 °C by the technique of sublimation epitaxy. We have studied two different cases: (i) the initial homoepitaxial growth of 6H-SiC followed by nucleation of 3C-SiC and (ii) nucleation of homoepitaxial 6H-SiC islands. The supersaturation in the growth cell was calculated using the modeled source to substrate temperature difference. We show that, at low temperature and supersaturation, growth of 6H-SiC commences in spiral growth mode, which prepares the surface for 3C-SiC nucleation. Provided the supersaturation is high enough, the 3C-SiC nucleates as two-dimensional islands on terraces of the homoepitaxial 6H-SiC. Detailed structural study indicates that the 3C-SiC began to grow on defect free surfaces. From the experimental and modeling results, we show that the growth parameter window for 3C-SiC is rather narrow. Deviation from it can result in 6H-SiC growth in spiral or 2D-nucleation mode, which suggests the importance of knowledge of supersaturation.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2012
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-73583 (URN)10.1021/cg200929r (DOI)000298726300030 ()
Note
Funding agencies|Swedish Research Council| 1220100821 |Research and Training Network - MANSiC| 035735 |Angpanneforeningen Research Foundation||Swedish Energy Agency||Bundesministerium fur Bildung und Forschung (BMBF)| 03SF0393 |Available from: 2012-01-09 Created: 2012-01-09 Last updated: 2017-12-08
3. Cubic SiC formation on the C-face of 6H-SiC (0001) substrates
Open this publication in new window or tab >>Cubic SiC formation on the C-face of 6H-SiC (0001) substrates
2012 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 348, no 1, 91-96 p.Article in journal (Refereed) Published
Abstract [en]

Nucleation and subsequent growth of cubic SiC (111) on Si- and C-faces of nominally on-axis 6H-SiC substrates was investigated.  More uniform nuclei and twin boundary distribution was observed when 3C-SiC was grown on the C-face. This was attributed to a lower critical supersaturation ratio. A new type of defects which appear as pits in the C-face 3C-SiC layers related to homoepitaxial  6H-SiC  spiral growth was found and described.  The evaluation  of the growth driving force for both polar faces showed that the homoepitaxial 6H-SiC spirals were not overgrown on the C-face  due to low maximum  supersaturation  ratio. The XRD ω-rocking  characterization shows a better structural quality of the 3C-SiC was grown on the Si-face, however on the C-face the uniformity over the whole sample was higher. Unintentional doping by N (~1016  cm-3) was slightly higher on the C-face while Al doping was higher (~1014  cm-3) on the Si-face of the grown material, similarly to the doping of hexagonal SiC polytypes.

Keyword
A1. Nucleation, A1. Characterization, A1. Polar surfaces A3. Vapor phase epitaxy, B1. Cubic Silicon Carbide.
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-76363 (URN)10.1016/j.jcrysgro.2012.03.053 (DOI)000303937900017 ()
Note
funding agencies|Swedish Research Council (VR)| 2008-5753 |Angpanneforeningens Forskningsstiftelse||Ericssons Research Foundation||Available from: 2012-04-05 Created: 2012-04-05 Last updated: 2017-12-07Bibliographically approved
4. Polytype transformation and structural characteristics of 3C-SiC on 6H-SiC substrates
Open this publication in new window or tab >>Polytype transformation and structural characteristics of 3C-SiC on 6H-SiC substrates
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2014 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 395, 109-115 p.Article in journal (Refereed) Published
Abstract [en]

The 3C-SiC (111) was grown on on-axis 6H-SiC substrates in a temperature interval ranging from 1675oC where 3C-SiC nucleated, to 1825oC where coverage of the substrate by 3C-SiC was  nearly  100%.  The  6H-  to  3C-SiC  transformation  was  not  abrupt  and  two  different transitions could be observed. The first one occurs before or during 3C-SiC nucleation and consists  of 6H-,  3C-, 15R-SiC  and other  unresolved  stacking  sequences.  The second  one appears due to 6H-SiC and 3C-SiC competition  during the growth and results in non flat needle-like interface. A proposed model elucidates connection between four-fold twins nucleating at the 6H-/3C-SiC interface and the formation of depressions at the surface of the 3C-SiC layer.

Keyword
Nucleation; Characterization; Crystal structure; Vapor phase cpitaxy; Cubic silicon carbide
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-76364 (URN)10.1016/j.jcrysgro.2014.03.021 (DOI)000335906000019 ()
Available from: 2012-04-05 Created: 2012-04-05 Last updated: 2017-12-07Bibliographically approved
5. Impact of extended defects on Hall and magnetoresistivity effects in cubic silicon carbide
Open this publication in new window or tab >>Impact of extended defects on Hall and magnetoresistivity effects in cubic silicon carbide
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2012 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 45, no 22, 225102- p.Article in journal (Refereed) Published
Abstract [en]

From magnetoresistivity effect measurements the carrier mobility at room- temperature is 200 cm2/Vs in heteroepitaxially grown 3C-SiC on 6H-SiC by sublimation epitaxy. The main scattering mechanisms are found to be scattering by neutral impurities at low temperature and by phonons at higher temperature. The carrier concentration is in the range of 1016  cm-3, which corresponds to the concentration of residual doping by nitrogen acquired  from  photoluminescence  measurements.  Using  magnetoresistance  and  Hall mobility data we have created a simple model which quantifies the volume of the samples influenced by extended defects. A higher doping near extended defects is either not present in the samples or might be screened by the electrostatic field created by these defects.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2012
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-76365 (URN)10.1088/0022-3727/45/22/225102 (DOI)000305175100004 ()
Available from: 2012-04-05 Created: 2012-04-05 Last updated: 2017-12-07Bibliographically approved
6. Influence of twin boundary orientation on magnetoresistivity effect in free standing 3C–SiC
Open this publication in new window or tab >>Influence of twin boundary orientation on magnetoresistivity effect in free standing 3C–SiC
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2012 (English)In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 74, 203-205 p.Article in journal (Refereed) Published
Abstract [en]

Free standing 3C–SiC (111) samples with differently oriented twin boundaries were prepared using on-axis and slightly off-axis 6H–SiC substrates. The orientation of twin boundaries causes either an enhancement or suppression of the magnetoresistance mobility. The origin of carrier mobility difference is attributed to the specific structure of these defects. The height of the barriers created by twin boundaries was found to be 0.2 eV.

Keyword
Magnetoresistance, Carrier mobility, Twin boundaries, 3C–SiC
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-76368 (URN)10.1016/j.matlet.2012.01.120 (DOI)000302763200058 ()
Note
funding agencies|Swedish Research Council| 1220100821 |Swedish Energy Agency||Available from: 2012-04-05 Created: 2012-04-05 Last updated: 2017-12-07Bibliographically approved
7. Growth of quality graphene on cubic silicon carbide
Open this publication in new window or tab >>Growth of quality graphene on cubic silicon carbide
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The growth of epitaxial graphene was performed on the Si-face of 4H-SiC, 6H-SiC and 3C-SiC substrates by Si sublimation of SiC in Ar atmosphere at a temperature of 2000oC. Graphene surface morphology and thickness have been evaluated using low-energy electron microscopy (LEEM)  and  atomic  force  microscopy   (AFM).  Large  homogeneous   areas  of  graphene monolayers (over 50x50 μm2) have been successfully grown on 3C-SiC substrates. Differences in the morphology of graphene layers, grown on different SiC polytypes, are related to a large extent to minimization of the terrace surface energy during the step bunching process. The uniformity  of  Si  sublimation  is  a  decisive  factor  for  obtaining  large  area  homogeneous graphene. It is also shown that better quality graphene is grown on 3C-SiC substrates with smoother  surface,  because of less pronounced  step bunching  and lower distribution  of step heights on polished surface.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-76370 (URN)
Available from: 2012-04-05 Created: 2012-04-05 Last updated: 2012-04-05Bibliographically approved

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