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  • 1.
    Bohnen, T.
    et al.
    Radboud University Nijmegen.
    Yazdi, Gholamreza
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    van Dreumel, G W G
    Radboud University Nijmegen.
    Hageman, P R
    Radboud University Nijmegen.
    Vlieg, E.
    Radboud University Nijmegen.
    Algra, R E
    Radboud University Nijmegen.
    Verheijen, M A
    Philips Res Labs.
    Edgar, J H
    Kansas State University.
    ScAlN nanowires: A cathodoluminescence study2009In: JOURNAL OF CRYSTAL GROWTH, ISSN 0022-0248, Vol. 311, no 11, p. 3147-3151Article in journal (Refereed)
    Abstract [en]

    Wurtzite ScAlN nanowires, grown on a scandium nitride (ScN) thin film by hydride vapor phase epitaxy (HVPE), were analyzed by energy dispersive analysis of X-rays (EDX), CL, high resolution transmission electron spectroscopy (HRTEM), and scanning electron microscopy (SEM). The wires were grown along the [0 0 0 1] axis, had an average length of 1 mu m, a diameter between 50 and 150 run, and a ScAlN composition with a 95:5 Al:Sc ratio. Cathodoluminescence studies on the individual wires showed a sharp emission near 2.4 eV, originating from the Sc atoms in the aluminum nitride (AlN) matrix. The formation of such a semiconducting ScAlN alloy could present a new alternative to InAlN for optoelectronic applications operating in the 200-550 nm range.

  • 2.
    Gogova, Daniela
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Larsson, Henrik
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Kasic, A.
    Yazdi, Gholam Reza
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Aujol, E.
    Frayssinet, E.
    Faurie, J-P.
    Beaumont, B.
    Gibart, P.
    High-Quality 2'' Bulk-Like Free-Standing GaN Grown by HydrideVapour Phase Epitaxy on a Si-doped Metal Organic Vapour Phase Epitaxial GaN Template with an Ultra Low Dislocation Density2005In: Japanese Journal of Applied Physics, ISSN 0021-4922, E-ISSN 1347-4065, Vol. 44, p. 1181-1185Article in journal (Refereed)
  • 3.
    Jokubavicius, Valdas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Sun, Jianwu
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Liu, Xinyu
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Yazdi, Gholamreza
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Growth optimization and applicability of thick on-axis SiC layers using sublimation epitaxy in vacuum2016In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 448, p. 51-57Article in journal (Refereed)
    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.

  • 4.
    Jokubavicius, Valdas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Yazdi, G. Reza
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Liljedahl, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Lateral Enlargement Growth Mechanism of 3C-SiC on Off-Oriented 4H-SiC Substrates2014In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 14, no 12, p. 6514-6520Article in journal (Refereed)
    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.

  • 5.
    Jokubavicius, Valdas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Yazdi, Gholam Reza
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Liljedahl, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Sun, Jianwu
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Liu, Xinyu
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Philipp, Schuh
    University of Erlangen, Erlangen, Germany.
    Wilhelm, Martin
    University of Erlangen, Erlangen, Germany.
    Wellmann, Peter
    University of Erlangen, Erlangen, Germany.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Single Domain 3C-SiC Growth on Off-Oriented 4H-SiC Substrates2015In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 15, no 6, p. 2940-2947Article in journal (Refereed)
    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.

  • 6.
    Khranovskyy, Volodymyr
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Tsiaoussis, I
    Aristotle University Thessaloniki.
    Yazdi, Gholamreza
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Heteroepitaxial ZnO nano hexagons on p-type SiC2010In: JOURNAL OF CRYSTAL GROWTH, ISSN 0022-0248, Vol. 312, no 2, p. 327-332Article in journal (Refereed)
    Abstract [en]

    ZnO single crystal nanohexagons have been grown heteroepitaxially on p-type Si-face 4H-SiC substrates with 8 degrees miscut from to [0 0 0 1] by catalyst-free atmospheric pressure metalorganic chemical vapor deposition and characterized by x-ray diffraction, scanning and transmission electron microscopy as well as energy disperse x-ray and cathodoluminescence analyses. The as-grown ZnO nanohexagons have a pillar shape terminated by a and c plane facets, and are aligned along the growth direction with the epitaxial relation [0 0 0 1](ZnO) parallel to[0 0 0 1](4H-SiC) and [1 0 (1) over bar 0](ZnO) parallel to[1 0 (1) over bar 0](4H-SiC). The ZnO nanohexagons demonstrate intense UV emission (lambda(NBE)=376 nm) and negligible defect-related luminescence.

  • 7.
    Khranovskyy, Volodymyr
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Yazdi, Gholamreza
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Larsson, Arvid
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Hussain, S
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Holtz, Per-Olof
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Yakimova, Rositsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Growth and characterization of ZnO nanostructured material2008In: Journal of Optoelectronics and Advanced Materials, ISSN 1454-4164, E-ISSN 1841-7132, Vol. 10, no 11, p. 2969-2975Article in journal (Refereed)
    Abstract [en]

    ZnO is a wide band gap (3.37 eV) semiconductor material with a high exciton binding energy (60 meV) at room temperature, which is a prerequisite for realization of efficient and stable optoelectronic systems. We demonstrated the APMOCVD growth of nanostructured ZnO material on Si and SiC with advanced emitting properties. The comparison of the properties of nanostructured polycrystalline layers with spatially disconnected ZnO nanocrystals clearly showed the advantage of the latter structures. Such structures distinctively luminesce in the UV range of the spectrum due to excitonic emission, while the contribution of the defect related luminescence is negligible. The significant improvement of the PL properties can be related to the decreased number of non-radiative recombination centers in the nanocrystals of high structural quality.

  • 8.
    Khranovskyy, Volodymyr
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Yazdi, Gholamreza
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Lashkarev, G.
    Inst Problems Mat Sci, UA-03680 Kiev, Ukraine.
    Ulyashin, A.
    Inst Energy Technol, N-2027 Kjeller, Norway.
    Yakimova, Rositsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Investigation of ZnO as a perspective material for photonics2008In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 205, no 1, p. 144-149Article in journal (Refereed)
    Abstract [en]

    Emissive properties of ZnO are of great interests in terms of the UV LED device design. The persistent "green" luminescence due to deep defect is an obstacle for obtaining an intense UV emission, expected from ZnO. We report the positive role of thermally diffused H toward quenching the defect emission in ZnO. It is suggested that hydrogen passivates defects responsible for DLE, resulting in efficient near band edge luminescence. As-grown ZnO/SiNx :H/Si films, deposited at 350 degrees C demonstrate intense narrow peaks of UV emission at 380 nm and a ratio of emission intensities, NBE/DLE approximate to 42. [GRAPHICS]

  • 9.
    Petoral, Rodrigo Jr
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Yazdi, Gholamreza
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Lloyd-Spets, Anita
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics.
    Yakimova, Rositsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Uvdal, Kajsa
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Organosilane-functionalized wide band gap semiconductor surfaces2007In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 90, no 22Article in journal (Refereed)
    Abstract [en]

    Surface functionalization of wide band gap semiconductors, SiC, ZnO, and GaN, with organosilane is reported. Formation of self-assembled monolayers of mercaptopropyltrimethoxysilane is confirmed by x-ray photoelectron spectroscopy and atomic force microscopy. The molecules are adsorbed on the surfaces through the silane groups with the free thiol groups molecularly oriented away from the surface. Moreover, chemisorption via the thiolate is observed for the ZnO surface. Immobilization of a model biomolecule to the functionalized surface is demonstrated. An amino acid derivative, i.e., phosphotyrosine derived thiol, is linked on the functionalized ZnO and GaN surfaces via formation of disulfide bridges. © 2007 American Institute of Physics.

  • 10.
    Petoral, Rodrigo Jr
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics .
    Yazdi, Gholamreza
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Vahlberg, Cecilia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics .
    Syväjärvi, Mikael
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Lloyd Spetz, Anita
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Uvdal, Kajsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics .
    Yakimova, Rositsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Surface Functionalization of SiC for Biosensor Applications2007In: ECSCRM 2006,2006, Material Science Forum, vol 556-557: Trans Tech Publications , 2007, p. 957-Conference paper (Refereed)
  • 11.
    Shi, Yuchen
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Jokubavicius, Valdas
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Höjer, Pontus
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Yazdi, Gholamreza
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Sun, Jianwu W.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    A comparative study of high-quality C-face and Si-face 3C-SiC(1 1 1) grown on off-oriented 4H-SiC substrates2019In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 52, no 34Article in journal (Refereed)
    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.

  • 12.
    Shi, Yuchen
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Zakharov, Alexei A.
    MAXIV Laboratory, Lund, Sweden.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Yazdi, Gholamreza Reza
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Jokubavicius, Valdas
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Sun, Jianwu
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Elimination of step bunching in the growth of large-area monolayer and multilayer graphene on off-axis 3CSiC (111)2018In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 140, p. 533-542Article in journal (Refereed)
    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.

    The full text will be freely available from 2020-08-24 11:11
  • 13.
    Shtepliuk, Ivan I.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. NASU, Ukraine.
    Vagin, Mikhail
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Iakimov, Tihomir
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Yazdi, Gholamreza
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Lead (Pb) interfacing with epitaxial graphene2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 25, p. 17105-17116Article in journal (Refereed)
    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.

  • 14.
    Sun, Jianwu W.
    et al.
    Université Montpellier 2 and CNRS, France.
    Khranovskyy, Volodymyr
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Mexis, M.
    Université Montpellier 2 and CNRS, France .
    Eriksson, Martin
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Tsiaoussis, I.
    Aristotle University of Thessaloniki, Greece.
    Yazdi, Gholamreza
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Peyre, H.
    Université Montpellier 2 and CNRS, France.
    Juillaguet, S.
    Université Montpellier 2 and CNRS, France.
    Camassel, J.
    Université Montpellier 2 and CNRS, France.
    Holtz, Per-Olof
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Bergman, Peder
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Comparative micro-photoluminescence investigation of ZnO hexagonal nanopillars and the seeding layer grown on 4H-SiC2012In: Journal of Luminescence, ISSN 0022-2313, E-ISSN 1872-7883, Vol. 132, no 1, p. 122-127Article in journal (Refereed)
    Abstract [en]

    We report on a comparative micro-photoluminescence investigation of ZnO hexagonal nanopillars (HNPs) and the seeding layer grown on the off-axis 4H-SiC substrate. Transmission electron microscope (TEM) results establish that a thin seeding layer continuously covers the terraces of 4H-SiC prior to the growth of ZnO HNPs. Low temperature photoluminescence (LTPL) shows that ZnO HNPs are only dominated by strong donor bound exciton emissions without any deep level emissions. Micro-LTPL mapping demonstrates that this is specific also for the seeding layer. To further understand the recombination mechanisms, time-resolved micro-PL spectra (micro-TRPL) have been collected at 5 K and identical bi-exponential decays have been found on both the HNPs and seeding layer. Temperature-dependent TRPL indicates that the decay time of donor bound exciton is mainly determined by the contributions of non-radiative recombinations. This could be explained by the TEM observation of the non-radiative defects in both the seeding layer and HNPs, like domain boundaries and dislocations, generated at the ZnO/SiC interface due to biaxial strain.

  • 15.
    Syväjärvi, Mikael
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Ciechonski, Rafal R.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Yazdi, Gholamreza R.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Fast epitaxy by PVT of SiC in hydrogen atmosphere2005In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 275, no 1-2, p. e1103-e1107 Article in journal (Refereed)
    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.

  • 16.
    Syväjärvi, Mikael
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Kakanakova-Georgieva, Anelia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Yazdi, Gholamreza
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Forsberg, Urban
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    A surface study of wet etched AlGaN epilayers grown by hot-wall MOCVD2007In: Journal of Crystal Growth, Vol. 300, 2007, Vol. 300, no 1, p. 242-245Conference paper (Refereed)
    Abstract [en]

    Epitaxial layers of AlGaN were grown by hot-wall MOCVD and their surfaces wet chemically etched with phosphorous acid. The as-grown surfaces and the development of the etched surfaces after 10 and 20 min of etching were studied with atomic force microscopy (AFM) and CL. In the as-grown layers growth features may be resolved while the RMS is as low as 1.4 Å in a scan area of 2×2 μm. Surfaces etched for 10 min had developed etch pits and a low RMS roughness of 7 Å indicating a uniform quality of the layers. Micrometer scale hexagonal features were observed after 20 min of etching. In some cases a deep hexagonal etch pit is observed in the centre of the hexagonal feature with a 30° rotation to each other, suggesting that the origin is substrate-induced defects. © 2006 Elsevier B.V. All rights reserved.

  • 17.
    Syväjärvi, Mikael
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Nasi, L.
    Yazdi, Gholamreza
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Salviati, G.
    Izadifard, Morteza
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Yakimova, Rositsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Formation of ferromagnetic SiC: Mn phases2005In: Materials Science Forum, Vols. 483-485, 2005, Vol. 483-485, p. 241-244Conference paper (Refereed)
    Abstract [en]

    Ferromagnetic phases in as-grown SiC have been studied. An interpretation about the formation based on details of the phase appearance in the layers from optical microscopy, AFM, and TEM investigations is related to the growth. Some phases were found to have a nucleation at the edge of the phase and detailed TEM investigations show that the phases have an increased grain density at the edge while the main part of the phase is monocrystalline.

  • 18.
    Vahlberg, Cecilia
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics .
    Yazdi, Gholam Reza
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Khranovskyy, V.
    Petoral, Rodrigo Jr
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics .
    Syväjärvi, Mikael
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Uvdal, Kajsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics .
    Lloyd-Spets, Anita
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Yakimova, Rositsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Surface engineering of functional materials for biosensors2006In: IEEE SENSORS 2005,2005, Proceedings IEEE SENSORS: ieee.org , 2006, p. 504-Conference paper (Refereed)
  • 19.
    Yakimova, Rositsa
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Iakimov, Tihomir
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Yazdi, Gholamreza
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Bouhafs, Chamseddine
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Eriksson, J.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Zakharov, A.
    MaxLab, Sweden .
    Boosalis, A.
    University of Nebraska, NE 68588 USA University of Nebraska, NE 68588 USA .
    Schubert, M.
    University of Nebraska, NE 68588 USA University of Nebraska, NE 68588 USA .
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Morphological and electronic properties of epitaxial graphene on SiC2014In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 439, p. 54-59Article in journal (Refereed)
    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.

  • 20.
    Yakimova, Rositsa
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kakanakova-Georgieva, Anelia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Yazdi, Gholamreza R.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Gueorguiev, Gueorgui K.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Sublimation growth of AlN crystals: Growth mode and structure evolution2005In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 281, no 1, p. 81-86Article in journal (Refereed)
    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.

  • 21.
    Yakimova, Rositsa
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Petoral, Rodrigo Jr
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Yazdi, Gholamreza
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Vahlberg, Cecilia
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Lloyd Spetz, Anita
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics.
    Uvdal, Kajsa
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Surface functionalization and biomedical applications based on SiC2007In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 40, no 20, p. 6435-6442Article in journal (Refereed)
    Abstract [en]

    The search for materials and systems, capable of operating long term under physiological conditions, has been a strategy for many research groups during the past years. Silicon carbide (SiC) is a material, which can meet the demands due to its high biocompatibility, high inertness to biological tissues and to aggressive environment, and the possibility to make all types of electronic devices. This paper reviews progress in biomedical and biosensor related research on SiC. For example, less biofouling and platelet aggregation when exposed to blood is taken advantage of in a variety of medical implantable materials while the robust semiconducting properties can be explored in surface functionalized bioelectronic devices. © 2007 IOP Publishing Ltd.

  • 22.
    Yakimova, Rositsa
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Steinhoff, Georg
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Petoral, Rodrigo Jr
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Vahlberg, Cecilia
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Khranovskyy, Volodymyr
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Yazdi, Gholamreza
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Uvdal, Kajsa
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Lloyd Spetz, Anita
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics.
    Novel material concepts of transducers for chemical and biosensors2007In: Biosensors & bioelectronics, ISSN 0956-5663, E-ISSN 1873-4235, Vol. 22, no 12, p. 2780-2785Article in journal (Refereed)
    Abstract [en]

    The objectives of this work are to contribute to the knowledge about physical and chemical properties of WBG semiconductors, such as ZnO and GaN towards development of advanced bio- and chemical sensors. For the semiconductors, growth techniques typically yielding single crystal material are applied. Thin epitaxial quality films of ZnO and GaN are fabricated on SiC or sapphire substrates. An emphasis is given to ZnO due to the interesting combination of the semiconductor and oxide properties. Surface bio-functionalization of ZnO is performed by APTES, MPA or MP-TMS molecules. We have compared some of the results to (hydroxylated) GaN surfaces functionalized by MP-TMS. The covalent attachment of the self-assembled biomolecular layers has been proven by XPS analysis. For complementary electrical characterization impedance spectroscopy measurements were performed. The results are intended to serve the realization of bioelectronic transducer devices based on SiC or GaN transistors with a ZnO gate layer. To take advantage of the catalytic properties of ZnO, initial prototypes of chemical sensors for gas sensing are processed on ZnO deposited either on SiC or on sapphire and they are further tested for the response to reducing or oxidizing gas ambient. The sensor devices show sensitivity to oxygen in the surface resistivity mode while a Pt Schottky contact ZnO/SiC device responds to reducing gases. These results are compared to published results on Pt/GaN Schottky diodes. © 2007 Elsevier B.V. All rights reserved.

  • 23.
    Yakimova, Rositsa
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Yazdi, Gholam Reza
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Nguyen, Son Tien
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Ivanov, Ivan Gueorguiev
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Syväjärvi, Mikael
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Sun, S.
    Tompa, G.
    Kuznetsov, A.
    Svensson, B.
    Optical and Morphological Features of Bulk and Homoepitaxial ZnO2006In: Superlattices and Microstructures, ISSN 0749-6036, E-ISSN 1096-3677, Vol. 39, p. 247-256Article in journal (Refereed)
    Abstract [en]

    ZnO substrate crystals from two different sources, and epitaxial layers have been studied by SEM, AFM, photoluminescence (T=2-135K) and EPR. Although fabricated by the same growth principle, i.e. the hydrothermal technique, the substrates differ in terms of purity and structural quality. In the PL spectra of all samples the dominating emission originates from the donor bound exciton (BE) recombination positioned at about 3361 meV. The temperature dependence of the spectra confirms the assignment of the free exciton emission in the purest sample, the line at 3376 meV evolves into a broad peak at higher temperatures, probably including both A and B excitons. Another FE-related emission appears as a shoulder on the high-energy side of FEA,B above 40 K. It is expected and associated with the crystal-field split-off counterpart of the valence band. Free-exciton related emission in the less pure sample can only be seen if the temperature is above 45 K. At T=135K all bound excitons are quenched and the spectrum in both samples consists of the free exciton no-phonon lines and their replicas. However, the emission from the pure samples is several orders of magnitude stronger than that from the other sample, which indicates strong non-radiative quenching of the excitons in the latter sample. The EPR measurements reveal a possible scenario of impurity re-arrangement, e.g. annealing at 950 °C may dissociate existing complexes and release Fe as isolated ions. The AFM and SEM investigations of an epilayer grown by MOCVD on one of the studied substrates have indicated growth instabilities and structural irregularities, thus pointing to the need for substrate quality and epitaxial process optimization.

  • 24.
    Yakimova, Rositsa
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Yazdi, Gholam Reza
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Sritirawisarn, N.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Structure Evolution of 3C-SiC on Cubic and Hexagonal Substrates2006In: Materials Science Forum, Vols. 527-529, 2006, Vol. 527-529, p. 283-286Conference paper (Refereed)
  • 25.
    Yakimova, Rositsa
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Yazdi, Gholamreza
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Iakimov, Tihomir
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Eriksson, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Applied Sensor Science. Linköping University, Faculty of Science & Engineering.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Challenges of Graphene Growth on Silicon Carbide2013In: ECS Transactions, Vol. 53, no 1, p. 9-16Article in journal (Refereed)
    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.

  • 26.
    Yazdi, G. Reza
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Vasiliauskas, Remigijus
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Iakimov, Tihomir
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Zakharov, A.
    Maxlab, Lund University, S-22100 Lund, Sweden.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Yakimova, Risitza
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Growth of quality graphene on cubic silicon carbideManuscript (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.

  • 27.
    Yazdi, Gholamreza
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Growth and Characterization of AlN: From Nano Structures to Bulk Material2008Doctoral 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.

    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, p. 81-86Article 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.

    Keywords
    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, p. e1103-e1107 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.

    Keywords
    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: 2018-01-13
    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, p. 127-130Article 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, p. 123103-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, p. 130-135 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.

    Keywords
    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, p. 935-939 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.

    Keywords
    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, p. 1031-1034Conference 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
    Keywords
    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, p. 082109-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).

    Keywords
    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
  • 28.
    Yazdi, Gholamreza R.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Persson, Per O. Å.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Gogova, Daniela
    Leibniz Institute for Crystal Growth, 12 489 Berlin, Germany.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Yakimova, Rosita
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Defect-free Single Crystal AlN Nanowires by Physical Vapor Transport GrowthManuscript (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.

  • 29.
    Yazdi, Gholamreza
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Beckers, Manfred
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Giuliani, Finn
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Freestanding AlN single crystals enabled by self-organization of 2H-SiC pyramids on 4H-SiC substrates2009In: APPLIED PHYSICS LETTERS, ISSN 0003-6951, Vol. 94, no 8, p. 082109-Article in journal (Refereed)
    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).

  • 30.
    Yazdi, Gholamreza
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Iakimov, Tihomir
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Epitaxial Graphene on SiC: A Review of Growth and Characterization2016In: Crystals, ISSN 2073-4352, Vol. 6, no 5, article id 53Article, review/survey (Refereed)
    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.

  • 31.
    Yazdi, Gholamreza
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Persson, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Gogova, D
    Leibniz Institute Crystal Growth.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Aligned AlN nanowires by self-organized vapor-solid growth2009In: NANOTECHNOLOGY, ISSN 0957-4484, Vol. 20, no 49, p. 495304-Article in journal (Refereed)
    Abstract [en]

    Highly oriented AlN single crystal nanowires with aspect ratio up to 600, diameter in the range of 40-500 nm, and 100 mu m lengths, have been synthesized via a vapor-solid growth mechanism. The results were obtained at 1750 degrees C and 850 mbar nitrogen pressure on vicinal SiC substrates pretreated by SiC sublimation epitaxy in order to attain distinguishable terraces. It was found that the nanowires change in thickness after they have reached a critical length, and this fact contributes to an understanding of the growth mechanism of AlN nanowires. The nanowires are hexagonally shaped and perfectly aligned along the [0001] direction with a small tilt given by the substrate vicinality. Under nitrogen excess a preferential growth along the c-axis of the wurtzite structure takes place while below some critical value of nitrogen pressure the growth mode switches to lateral. The AlN nanowires are shown to have a dislocation free wurtzite crystal structure. Some possible applications are discussed.

  • 32.
    Yazdi, Gholamreza
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Vasiliauskas, Remigijus
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Employing discontinuous and continuous growth modes for preparation of AlN nanostructures on SiC substrates2007In: ECSCRM 2006, Newcastle, UK: Materials Science Forum Vols. 556-557, Trans Tech Publications, Switzerland , 2007, Vol. 556-557, p. 1031-1034Conference 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.

  • 33.
    Yazdi, Gholamreza
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Aligned AlN nanowires and microrods by self-patterning2007In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 90, no 12, p. 123103-Article in journal (Refereed)
    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.

  • 34.
    Yazdi, Gholamreza
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Formation of needle-like and columnar structures of AlN2007In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 300, no 1, p. 130-135 Article in journal (Refereed)
    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.

  • 35.
    Yazdi, Gholamreza
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Growth and morphology of AlN crystals2006In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T126, p. 127-130Article in journal (Refereed)
    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.

  • 36.
    Yazdi, Gholamreza
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Syväjärvi, Mikael
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Yakimova, Rositsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Novel approach to AlN growth for power device applications2007In: WASMPE 2007,2007, 2007, p. 29-30Conference paper (Other academic)
  • 37.
    Yazdi, Gholamreza
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Vasiliauskas, Remigijus
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Iakimov, Tihomir
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Zakharov, Alexei
    Lund University, Sweden .
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Growth of large area monolayer graphene on 3C-SiC and a comparison with other SiC polytypes2013In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 57, p. 477-484Article in journal (Refereed)
    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.

  • 38.
    Yazdi, Gholamreza
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Vasiliauskas, Remigijus
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Fabrication of free-standing AlN crystals by controlled microrod growth2008In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 300, no 5, p. 935-939 Article in journal (Refereed)
    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.

  • 39.
    Yazdi, Gholamreza
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Vassilevski, K.
    Newcastle University.
    Cordoba Gallego, Jose Manuel
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials . Linköping University, The Institute of Technology.
    Gogova, Daniela
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Nikitina, I. P.
    Newcastle University.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials . Linköping University, The Institute of Technology.
    Wright, N.G.
    Newcastle University.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Free standing AIN single crystal grown on pre-patterned and in situ patterned 4H-SiC substrates2010In: Materials Science Forum, Vols. 645-648, Transtec Publications; 1999 , 2010, Vol. 645-648, p. 1187-1190Conference paper (Refereed)
    Abstract [en]

    Free standing AIN wafers were grown on pre-patterned and in situ patterned 4H-SiC substrates by a physical vapor transport method. It is based on the coalescence of AIN microrods, which evolve from the apex of SiC pyramids grown on the SIC substrate during a temperature ramp up for in situ patterned substrate and SiC pyramids formed by reactive ion etching (RIE). This process yields stress-free (according XRD and Raman results) AIN single crystals with a thickness up to 400 mu m and low dislocation density.

1 - 39 of 39
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