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Yazdi, Gholamreza
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Shi, Y., Jokubavicius, V., Höjer, P., Ivanov, I. G., Yazdi, G., Yakimova, R., . . . Sun, J. W. (2019). A comparative study of high-quality C-face and Si-face 3C-SiC(1 1 1) grown on off-oriented 4H-SiC substrates. Journal of Physics D: Applied Physics, 52(34)
Öppna denna publikation i ny flik eller fönster >>A comparative study of high-quality C-face and Si-face 3C-SiC(1 1 1) grown on off-oriented 4H-SiC substrates
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2019 (Engelska)Ingår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 52, nr 34Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We present a comparative study of the C-face and Si-face of 3C-SiC(111) grown on off-oriented 4H-SiC substrates by the sublimation epitaxy. By the lateral enlargement method, we demonstrate that the high-quality bulk-like C-face 3C-SiC with thickness of ~1 mm can be grown over a large single domain without double positioning boundaries (DPBs), which are known to have a strongly negative impact on the electronic properties of the material. Moreover, the C-face sample exhibits a smoother surface with one unit cell height steps while the surface of the Si-face sample exhibits steps twice as high as on the C-face due to step-bunching. High-resolution XRD and low temperature photoluminescence measurements show that C-face 3C-SiC can reach the same high crystalline quality as the Si-face 3C-SiC. Furthermore, cross-section studies of the C- and Si-face 3C-SiC demonstrate that in both cases an initial homoepitaxial 4H-SiC layer followed by a polytype transition layer are formed prior to the formation and lateral expansion of 3C-SiC layer. However, the transition layer in the C-face sample is extending along the step-flow direction less than that on the Si-face sample, giving rise to a more fairly consistent crystalline quality 3C-SiC epilayer over the whole sample compared to the Si-face 3C-SiC where more defects appeared on the surface at the edge. This facilitates the lateral enlargement of 3C-SiC growth on hexagonal SiC substrates.

Ort, förlag, år, upplaga, sidor
Biopress Ltd, 2019
Nationell ämneskategori
Den kondenserade materiens fysik
Identifikatorer
urn:nbn:se:liu:diva-159101 (URN)10.1088/1361-6463/ab2859 (DOI)000475964100002 ()
Anmärkning

Funding agencies:  Swedish Research Council (Vetenskapsradet) [621-2014-5461, 2018-04670, 2016-05362, 621-2014-5825]; Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS) [2016-00559]; Swedish Foundation for International Cooperation

Tillgänglig från: 2019-07-24 Skapad: 2019-07-24 Senast uppdaterad: 2019-08-07
Shi, Y., Zakharov, A. A., Ivanov, I. G., Yazdi, G. R., Jokubavicius, V., Syväjärvi, M., . . . Sun, J. (2018). Elimination of step bunching in the growth of large-area monolayer and multilayer graphene on off-axis 3CSiC (111). Carbon, 140, 533-542
Öppna denna publikation i ny flik eller fönster >>Elimination of step bunching in the growth of large-area monolayer and multilayer graphene on off-axis 3CSiC (111)
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2018 (Engelska)Ingår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 140, s. 533-542Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Multilayer graphene has exhibited distinct electronic properties such as the tunable bandgap for optoelectronic applications. Among all graphene growth techniques, thermal decomposition of SiC is regarded as a promising method for production of device-quality graphene. However, it is still very challenging to grow uniform graphene over a large-area, especially multilayer graphene. One of the main obstacles is the occurrence of step bunching on the SiC surface, which significantly influences the formation process and the uniformity of the multilayer graphene. In this work, we have systematically studied the growth of monolayer and multilayer graphene on off-axis 3CSiC(111). Taking advantage of the synergistic effect of periodic SiC step edges as graphene nucleation sites and the unique thermal decomposition energy of 3CSiC steps, we demonstrate that the step bunching can be fully eliminated during graphene growth and large-area monolayer, bilayer, and four-layer graphene can be controllably obtained on high-quality off-axis 3CSiC(111) surface. The low energy electron microscopy results demonstrate that a uniform four-layer graphene has been grown over areas of tens of square micrometers, which opens the possibility to tune the bandgap for optoelectronic devices. Furthermore, a model for graphene growth along with the step bunching elimination is proposed.

Ort, förlag, år, upplaga, sidor
Elsevier, 2018
Nationell ämneskategori
Materialkemi
Identifikatorer
urn:nbn:se:liu:diva-151054 (URN)10.1016/j.carbon.2018.08.042 (DOI)000450120200057 ()
Anmärkning

Funding agencies: Swedish Research Council (Vetenskapsradet) [621-2014-5461, 621-2014-5825]; Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS) [2016-00559]; Swedish Foundation for International Cooperation in Research and Higher 

Tillgänglig från: 2018-09-12 Skapad: 2018-09-12 Senast uppdaterad: 2019-07-24
Shtepliuk, I. I., Vagin, M., Ivanov, I. G., Iakimov, T., Yazdi, G. & Yakimova, R. (2018). Lead (Pb) interfacing with epitaxial graphene. Physical Chemistry, Chemical Physics - PCCP, 20(25), 17105-17116
Öppna denna publikation i ny flik eller fönster >>Lead (Pb) interfacing with epitaxial graphene
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2018 (Engelska)Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, nr 25, s. 17105-17116Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Here, we report the electrochemical deposition of lead (Pb) as a model metal on epitaxial graphene fabricated on silicon carbide (Gr/SiC). The kinetics of electrodeposition and morphological characteristics of the deposits were evaluated by complementary electrochemical, physical and computational methods. The use of Gr/SiC as an electrode allowed the tracking of lead-associated redox conversions. The analysis of current transients passed during the deposition revealed an instantaneous nucleation mechanism controlled by convergent mass transport on the nuclei locally randomly distributed on epitaxial graphene. This key observation of the deposit topology was confirmed by low values of the experimentally-estimated apparent diffusion coefficient, Raman spectroscopy and scanning electron microscopy (SEM) studies. First principles calculations showed that the nucleation of Pb clusters on the graphene surface leads to weakening of the interaction strength of the metal-graphene complex, and only spatially separated Pb adatoms adsorbed on bridge and/or edge-plane sites can affect the vibrational properties of graphene. We expect that the lead adatoms can merge in large metallic clusters only at defect sites that reinforce the metal-graphene interactions. Our findings provide valuable insights into both heavy metal ion electrochemical analysis and metal electroplating on graphene interfaces that are important for designing effective detectors of toxic heavy metals.

Ort, förlag, år, upplaga, sidor
Royal Society of Chemistry, 2018
Nationell ämneskategori
Den kondenserade materiens fysik
Identifikatorer
urn:nbn:se:liu:diva-149854 (URN)10.1039/c8cp01814f (DOI)000436571800024 ()29896595 (PubMedID)
Anmärkning

Funding Agencies|VR grant [621-2014-5805]; SSF [SSF GMT14-0077, SSF RMA15-0024]; Angpanneforeningens Forskningsstiftelse [16-541]

Tillgänglig från: 2018-08-02 Skapad: 2018-08-02 Senast uppdaterad: 2018-08-20
Yazdi, G., Iakimov, T. & Yakimova, R. (2016). Epitaxial Graphene on SiC: A Review of Growth and Characterization. Crystals, 6(5), Article ID 53.
Öppna denna publikation i ny flik eller fönster >>Epitaxial Graphene on SiC: A Review of Growth and Characterization
2016 (Engelska)Ingår i: Crystals, ISSN 2073-4352, Vol. 6, nr 5, artikel-id 53Artikel, forskningsöversikt (Refereegranskat) Published
Abstract [en]

This review is devoted to one of the most promising two-dimensional (2D) materials, graphene. Graphene can be prepared by different methods and the one discussed here is fabricated by the thermal decomposition of SiC. The aim of the paper is to overview the fabrication aspects, growth mechanisms, and structural and electronic properties of graphene on SiC and the means of their assessment. Starting from historical aspects, it is shown that the most optimal conditions resulting in a large area of one ML graphene comprise high temperature and argon ambience, which allow better controllability and reproducibility of the graphene quality. Elemental intercalation as a means to overcome the problem of substrate influence on graphene carrier mobility has been described. The most common characterization techniques used are low-energy electron microscopy (LEEM), angle-resolved photoelectron spectroscopy (ARPES), Raman spectroscopy, atomic force microscopy (AFM) in different modes, Hall measurements, etc. The main results point to the applicability of graphene on SiC in quantum metrology, and the understanding of new physics and growth phenomena of 2D materials and devices.

Ort, förlag, år, upplaga, sidor
MDPI AG, 2016
Nyckelord
graphene; epitaxial; SiC; sublimation
Nationell ämneskategori
Den kondenserade materiens fysik
Identifikatorer
urn:nbn:se:liu:diva-129674 (URN)10.3390/cryst6050053 (DOI)000377262000006 ()
Anmärkning

Funding Agencies|European Union Seventh Framework Program [604391]; Swedish Research Council [VR 621-2014-5805]; SSF; KAW funding

Tillgänglig från: 2016-06-27 Skapad: 2016-06-23 Senast uppdaterad: 2017-11-28
Jokubavicius, V., Sun, J., Liu, X., Yazdi, G., Ivanov, I. G., Yakimova, R. & Syväjärvi, M. (2016). Growth optimization and applicability of thick on-axis SiC layers using sublimation epitaxy in vacuum. Journal of Crystal Growth, 448, 51-57
Öppna denna publikation i ny flik eller fönster >>Growth optimization and applicability of thick on-axis SiC layers using sublimation epitaxy in vacuum
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2016 (Engelska)Ingår i: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 448, s. 51-57Artikel i tidskrift (Refereegranskat) 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.

Nyckelord
Mass transfer;Substrates;Single crystal growth;Semiconducting materials
Nationell ämneskategori
Materialkemi
Identifikatorer
urn:nbn:se:liu:diva-128610 (URN)10.1016/j.jcrysgro.2016.05.017 (DOI)
Tillgänglig från: 2016-05-25 Skapad: 2016-05-25 Senast uppdaterad: 2017-11-30
Jokubavicius, V., Yazdi, G. R., Liljedahl, R., Ivanov, I. G., Sun, J., Liu, X., . . . Syväjärvi, M. (2015). Single Domain 3C-SiC Growth on Off-Oriented 4H-SiC Substrates. Crystal Growth & Design, 15(6), 2940-2947
Öppna denna publikation i ny flik eller fönster >>Single Domain 3C-SiC Growth on Off-Oriented 4H-SiC Substrates
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2015 (Engelska)Ingår i: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 15, nr 6, s. 2940-2947Artikel i tidskrift (Refereegranskat) 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.

Ort, förlag, år, upplaga, sidor
American Chemical Society (ACS), 2015
Nationell ämneskategori
Materialkemi
Identifikatorer
urn:nbn:se:liu:diva-118525 (URN)10.1021/acs.cgd.5b00368 (DOI)000355890400051 ()
Anmärkning

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

Tillgänglig från: 2015-05-29 Skapad: 2015-05-29 Senast uppdaterad: 2017-12-04
Jokubavicius, V., Yazdi, G. R., Liljedahl, R., Ivanov, I. G., Yakimova, R. & Syväjärvi, M. (2014). Lateral Enlargement Growth Mechanism of 3C-SiC on Off-Oriented 4H-SiC Substrates. Crystal Growth & Design, 14(12), 6514-6520
Öppna denna publikation i ny flik eller fönster >>Lateral Enlargement Growth Mechanism of 3C-SiC on Off-Oriented 4H-SiC Substrates
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2014 (Engelska)Ingår i: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 14, nr 12, s. 6514-6520Artikel i tidskrift (Refereegranskat) 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.

Ort, förlag, år, upplaga, sidor
American Chemical Society (ACS), 2014
Nationell ämneskategori
Fysik Kemi
Identifikatorer
urn:nbn:se:liu:diva-112510 (URN)10.1021/cg501424e (DOI)000345884000043 ()
Tillgänglig från: 2014-11-29 Skapad: 2014-11-29 Senast uppdaterad: 2017-12-05Bibliografiskt granskad
Yakimova, R., Iakimov, T., Yazdi, G., Bouhafs, C., Eriksson, J., Zakharov, A., . . . Darakchieva, V. (2014). Morphological and electronic properties of epitaxial graphene on SiC. Physica. B, Condensed matter, 439, 54-59
Öppna denna publikation i ny flik eller fönster >>Morphological and electronic properties of epitaxial graphene on SiC
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2014 (Engelska)Ingår i: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 439, s. 54-59Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We report on the structural and electronic properties of graphene grown on SiC by high-temperature sublimation. We have studied thickness uniformity of graphene grown on 4H-SiC (0 0 0 1), 6H-SiC (0 0 0 1), and 3C-SiC (1 1 1) substrates and investigated in detail graphene surface morphology and electronic properties. Differences in the thickness uniformity of the graphene layers on different SiC polytypes is related mainly to the minimization of the terrace surface energy during the step bunching process. It is also shown that a lower substrate surface roughness results in more uniform step bunching and consequently better quality of the grown graphene. We have compared the three SiC polytypes with a clear conclusion in favor of 3C-SiC. Localized lateral variations in the Fermi energy of graphene are mapped by scanning Kelvin probe microscopy It is found that the overall single-layer graphene coverage depends strongly on the surface terrace width, where a more homogeneous coverage is favored by wider terraces, It is observed that the step distance is a dominating, factor in determining the unintentional doping of graphene from the SiC substrate. Microfocal spectroscopic ellipsometry mapping of the electronic properties and thickness of epitaxial graphene on 3C-SiC (1 1 1) is also reported. Growth of one monolayer graphene is demonstrated on both Si- and C-polarity of the 3C-SiC substrates and it is shown that large area homogeneous single monolayer graphene can be achieved on the Si-face substrates. Correlations between the number of graphene monolayers on one hand and the main transition associated with an exciton enhanced van Hove singularity at similar to 4.5 eV and the free-charge carrier scattering time, on the other are established It is shown that the interface structure on the Si- and C-polarity of the 3C-SiC (1 1 1) differs and has a determining role for the thickness and electronic properties homogeneity of the epitaxial graphene.

Ort, förlag, år, upplaga, sidor
Elsevier, 2014
Nyckelord
Epitaxial graphene; Sublimation of SiC; Electronic properties; Step-bunching; Spectroscopic ellipsometry mapping
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
urn:nbn:se:liu:diva-105565 (URN)10.1016/j.physb.2013.12.048 (DOI)000331620700012 ()
Tillgänglig från: 2014-03-31 Skapad: 2014-03-27 Senast uppdaterad: 2017-12-05
Yakimova, R., Yazdi, G., Iakimov, T., Eriksson, J. & Darakchieva, V. (2013). Challenges of Graphene Growth on Silicon Carbide. ECS Transactions, 53(1), 9-16
Öppna denna publikation i ny flik eller fönster >>Challenges of Graphene Growth on Silicon Carbide
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2013 (Engelska)Ingår i: ECS Transactions, Vol. 53, nr 1, s. 9-16Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

One of the main challenges in the fabrication of device quality graphene is the achievement of large area monolayer graphene that is processing compatible. Here, the impact of the substrate properties on the thickness uniformity and electronic characteristics for epitaxial graphene on SiC produced by high temperature sublimation has been evidenced and discussed. Several powerful techniques have been used to collect data, among them large scale ellipsometry mapping has been demonstrated for the first time. The study is covering all three SiC polytype, e.g. 4H-, 6H- and 3C-SiC in order to reveal eventual peculiarities that have to be controlled during graphene growth. The advantage of the cubic polytype is unambiguously demonstrated.

Nationell ämneskategori
Den kondenserade materiens fysik
Identifikatorer
urn:nbn:se:liu:diva-118762 (URN)10.1149/05301.0009ecst (DOI)
Tillgänglig från: 2015-06-03 Skapad: 2015-06-03 Senast uppdaterad: 2015-06-18
Yazdi, G., Vasiliauskas, R., Iakimov, T., Zakharov, A., Syväjärvi, M. & Yakimova, R. (2013). Growth of large area monolayer graphene on 3C-SiC and a comparison with other SiC polytypes. Carbon, 57, 477-484
Öppna denna publikation i ny flik eller fönster >>Growth of large area monolayer graphene on 3C-SiC and a comparison with other SiC polytypes
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2013 (Engelska)Ingår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 57, s. 477-484Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Epitaxial graphene growth was performed on the Si-terminated face of 4H-, 6H-, and 3C-SiC substrates by silicon sublimation from SiC in argon atmosphere at a temperature of 2000 degrees C. Graphene surface morphology, thickness and band structure have been assessed by using atomic force microscopy, low-energy electron microscopy, and angle-resolved photoemission spectroscopy, respectively. Differences in the morphology of the graphene layers on different SiC polytypes is related mainly to the minimization of the terrace surface energy during the step bunching process. The uniformity of silicon sublimation is a decisive factor for obtaining large area homogenous graphene. It is also shown that a lower substrate surface roughness results in more uniform step bunching with a lower distribution of step heights and consequently better quality of the grown graphene. Large homogeneous areas of graphene monolayers (over 50 x 50 mu m(2)) have been grown on 3C-SiC (1 1 1) substrates. The comparison with the other polytypes suggests a similarity in the surface behaviour of 3C- and 6H-SiC.

Ort, förlag, år, upplaga, sidor
Elsevier, 2013
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
urn:nbn:se:liu:diva-94597 (URN)10.1016/j.carbon.2013.02.022 (DOI)000319030000055 ()
Anmärkning

Funding Agencies|FP7 EU project Concept Graphene and the Swedish Research Council (VR)|2011-44472010-3511 Grafic ESF|

Tillgänglig från: 2013-06-27 Skapad: 2013-06-27 Senast uppdaterad: 2017-12-06
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