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  • 101.
    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.

  • 102.
    Jokubavicius, Valdas
    et al.
    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.
    Silicon Carbide Surface Cleaning and Etching2018In: Advancing Silicon Carbide Electronics Technology I / [ed] Konstantinos Zekentes and Konstantin Vasilevskiy, Materials Research Forum LLC , 2018, p. 1-26Chapter in book (Refereed)
    Abstract [en]

    Silicon carbide (SiC) surface cleaning and etching (wet, electrochemical, thermal) are important technological processes in preparation of SiC wafers for crystal growth, defect analysis or device processing. While removal of organic, particulate and metallic contaminants by chemical cleaning is a routine process in research and industrial production, the etching which, in addition to structural defects analysis, can also be used to modify wafer surface structure, is very interesting for development of innovative device concepts. In this book chapter we review SiC chemical cleaning and etching procedures and present perspectives of SiC etching for new device development.

  • 103.
    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.

  • 104.
    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.

  • 105.
    Junige, Marcel
    et al.
    Technical University of Dresden, Germany.
    Oddoy, Tim
    Technical University of Dresden, Germany.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Wenger, Christian
    IHP GmbH, Germany.
    Lupina, Grzegorz
    IHP GmbH, Germany.
    Kitzmann, Julia
    IHP GmbH, Germany.
    Albert, Matthias
    Technical University of Dresden, Germany.
    Bartha, Johann W.
    Technical University of Dresden, Germany.
    Atomic Layer Deposition of Al2O3 on NF3-pre-treated graphene2015In: NANOTECHNOLOGY VII, Society of Photo-optical Instrumentation Engineers (SPIE) , 2015, Vol. 9519, no 951915Conference paper (Refereed)
    Abstract [en]

    Graphene has been considered for a variety of applications including novel nanoelectronic device concepts. However, the deposition of ultra-thin high-k dielectrics on top of graphene has still been challenging due to graphenes lack of dangling bonds. The formation of large islands and leaky films has been observed resulting from a much delayed growth initiation. In order to address this issue, we tested a pre-treatment with NF3 instead of XeF2 on CVD graphene as well as epitaxial graphene monolayers prior to the Atomic Layer Deposition (ALD) of Al2O3. All experiments were conducted in vacuo; i. e. the pristine graphene samples were exposed to NF3 in the same reactor immediately before applying 30 (TMA-H2O) ALD cycles and the samples were transferred between the ALD reactor and a surface analysis unit under high vacuum conditions. The ALD growth initiation was observed by in-situ real-time Spectroscopic Ellipsometry (irtSE) with a sampling rate above 1Hz. The total amount of Al2O3 material deposited by the applied 30 ALD cycles was cross-checked by in-vacuo X-ray Photoelectron Spectroscopy (XPS). The Al2O3 morphology was determined by Atomic Force Microscopy (AFM). The presence of graphene and its defect status was examined by in-vacuo XPS and RAMAN Spectroscopy before and after the coating procedure, respectively.

  • 106.
    Kakanakova-Georgieva, Anelia
    et al.
    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.
    Magnusson, Björn
    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.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Growth of AlN films by hot-wall CVD and sublimation techniques: Effect of growth cell pressure2002In: Materials Science Forum, Vols. 389-393, 2002, Vol. 389-3, p. 1469-1472Conference paper (Refereed)
    Abstract [en]

    Aluminum nitride (AlN) films were grown on off-axis, Si-terminated 4H-SiC substrates by hot-wall CVD and sublimation techniques. The films were investigated by Infrared reflectance, Optical microscopy, Energy Dispersive X-ray analysis and Cathodoluminescence in a Scanning Electron Microscope with respect to their thickness, morphological, compositional and luminescence properties, in order to examine the influence of the growth cell pressure in either of the two deposition methods. Good quality thick AlN films were obtained by hot-wall CVD at temperature of 1200degreesC and reduced pressure of 100 mbar as reflected in the near stoichiometric N/Al ratio in these layers and in the appearance of the characteristic AlN near band edge emission. The AlN sublimation grown films at temperature of 2100degreesC suffered from island growth irrespective of the background pressure. The supersaturation conditions that affect strongly the growth mode became more favorable when the temperature was reduced to 1900degreesC.

  • 107.
    Kakanakova-Georgieva, Anelia
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Gueorguiev, Gueorgui Kostov
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Yakimova, Rositsa
    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.
    Effect of impurity incorporation on crystallization in AlN sublimation epitaxy2004In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 96, no 9, p. 5293-5297Article in journal (Refereed)
    Abstract [en]

    We have implemented graphite, graphite-tantalum (Ta), and Ta growth environment to the sublimation epitaxy of aluminum nitride (AlN) and have studied development, morphological, and cathodoluminescence emission properties of AlN crystallites. Three apparently different types of crystallites form in the three different types of growth environment, which presumably manifests the relationship between crystallite-habit-type and impurities. Comparison between the cathodoluminescence spectra reveals certain dynamics in the incorporation into AlN of the main residual dopants, oxygen and carbon, when the growth environment changes. At high temperatures, in addition to Al and N2, which constitute the vapor over AlN, vapor molecules of CN, NO, Al2C, and many more can be present in the vapor from which AlN grows and both oxygen and carbon can be incorporated into AlN in varying ratios. Involving calculations of the cohesive energy per atom of such vapor molecules and also of Ta containing molecules, we have considered possible mechanisms how oxygen and carbon get incorporated into AlN and how this kinetics interferes with the growth environment. The positive effect of Ta consists in the marked reduction of residual oxygen and carbon impurities in the vapor from which AlN is growing. However, on the account of this reduction, the overall composition of the vapor changes. We speculate that during AlN nucleation stage small impurity levels may be beneficial in order to provide a better balance between the AlN crystallites development and impurity incorporation issues. We have shown that some impurity containing vapor molecules are acting as essential transport agents and suppliers of nitrogen for the AlN growth. © 2004 American Institute of Physics.

  • 108.
    Kakanakova-Georgieva, Anelia
    et al.
    Sofia University.
    Paskova, T.
    Sofia University.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hallin, Christer
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Trifonova, E.P.
    Sofia University.
    Surtchev, M.
    Sofia University.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Structural properties of 6H-SiC epilayers grown by two different techniques1997In: Materials Science and Engineering B, ISSN 0921-5107, Vol. 46, no 1-3, p. 345-348Article in journal (Refereed)
    Abstract [en]

    In the present work we investigated the structural properties of 6H-SiC homoepitaxial layers utilizing microhardness and X-ray characterization techniques. The growth was performed by chemical vapour deposition (CVD) and liquid phase epitaxy (LPE) under various growth conditions. The depth Knoop hardness profiles represent decreasing curves due to the indentation size effect. With load increasing the curves saturate reaching microhardness values comparable with the known Vickers ones. At about 0.4 μm beneath the layer surfaces the curves show small plateaus which may be attributed to structural inhomogeneity. This is suggested by X-ray diffraction spectra taken from the same samples, which contain additional peaks besides the typical ones for 6H-SiC.

  • 109.
    Kakanakova-Georgieva, Anelia
    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.
    Yakimova, Rositsa
    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.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Sublimation epitaxy of AlN on SiC: Growth morphology and structural features2004In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 273, no 1-2, p. 161-166Article in journal (Refereed)
    Abstract [en]

    In order to study the development of individual AlN crystallites, sublimation epitaxy of AlN was performed on 4H-SiC, off-axis substrates in an inductively heated setup. Growth process variables like temperature, extrinsic nitrogen pressure and time were changed in an attempt to favor the lateral growth of individual AlN crystallites and thus open possibilities to prepare continuous patterns. Scanning and transmission electron microscopy and cathodoluminescence were used to obtain plan-view and cross-sectional images of the grown patterns and to study their morphology and structural features. The growth at 1900°C/200mbar results in AlN pattern consisting of individual single wurzite AlN crystallites with plate-like shape aligned along [1 1̄ 0 0] direction. The only defects these AlN crystallites contain are threading dislocations, some of which are terminated by forming half-loops. Because of the uniform distribution of the crystallites and their high structural perfection, this AlN pattern could represent interest as a template for bulk AlN growth. Alternative growth approaches to AlN crystallite formation are possible resulting in variation of the final AlN pattern structure. From a viewpoint of obtaining continuous patterns, the more favorable growth conditions involve applying of increased extrinsic gas pressure, 700 mbar in our case. © 2004 Elsevier B.V. All rights reserved.

  • 110.
    Kakanakova-Georgieva, Anelia
    et al.
    University of Sofia.
    Trifonova, E.P.
    University of Sofia.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    MacMillan, M.F.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Microhardness of 6H-SiC epitaxial layers grown by sublimation1999In: Crystal research and technology (1981), ISSN 0232-1300, E-ISSN 1521-4079, Vol. 34, no 8, p. 943-947Article in journal (Refereed)
    Abstract [en]

    Knoop microhardness of 6H-SiC layers grown by sublimation epitaxy was investigated. The microhardness-load curves for all of the samples were measured and then used to extract the load-independent microhardness values. The relationships of these values to the growth time and growth rate were studied. The microhardness-depth profiles indicated that the layer/substrate interface region had a microhardness value that differed significantly from that of both the epi-layer and the substrate.

  • 111.
    Kakanakova-Georgieva, Anelia
    et al.
    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.
    Gueorguiev, G.K.
    Departamento De Fisica Da Universidade, 3004-516 Coimbra, Portugal.
    Linnarsson, M.K.
    Solid State Electronics, Royal Institute of Technology, P.O. Box E229, S-164 40 Kista, Sweden.
    Syväjärvi, Mikael
    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.
    Kinetics of residual doping in 4H-SiC epitaxial layers grown in vacuum2002In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 240, no 3-4, p. 501-507Article in journal (Refereed)
    Abstract [en]

    Investigation on residual Al, B, and N co-doping of 4H-SiC epitaxial layers is reported. The layers were produced by sublimation epitaxy in Ta growth cell environment at different growth temperatures and characterized by secondary ion mass spectrometry. The vapor interaction with Ta was considered through calculations of cohesive energies of several Si-, Al-, B-, and N-containing vapor molecules and also of diatomic Ta-X molecules. An analysis of kinetic mechanisms responsible for impurity incorporation is performed. Among residuals, B exhibits a stronger incorporation dependence on temperature and growth at lower temperatures can favor B decrease in the layers. Under the growth conditions in this study (Ta environment and presence of attendant Al and N), B incorporation is assisted by Si2C vapor molecule. Boron tends to occupy carbon sites at higher temperatures, i.e. higher growth rates. © 2002 Elsevier Science B.V. All rights reserved.

  • 112.
    Kakanakova-Georgieva, Anelia
    et al.
    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.
    Henry, Anne
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Linnarsson, M.K.
    Royal Institute of Technology, PO Box E229, S-16440 Kista, Sweden.
    Syväjärvi, Mikael
    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.
    Cathodoluminescence identification of donor-acceptor related emissions in as-grown 4H-SiC layers2002In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 91, no 5, p. 2890-2895Article in journal (Refereed)
    Abstract [en]

    A comparative analysis of cathodoluminescence spectra in 4H-SiC layers with different N, Al, and B content is reported. The layers were produced by sublimation epitaxy and residual impurity concentrations were determined by secondary ion mass spectrometry. Epilayers doped with B in a wide concentration range, 5×1015-3×1018cm-3, were achieved. Evidence of N, Al, and B related emissions by cathodoluminescence experiments is presented. Differences in the luminescence emitted by the layers are established that are attributed to different B content and impurity cooperation. The characteristics of broad green emission, originating from B-related centers, at 4.6 K, 300 K, as well as in high temperature annealed layers are discussed. The experimental results suggest that boron is involved in more than one deep acceptor center. © 2002 American Institute of Physics.

  • 113.
    Kakanakova-Georgieva, Anelia
    et al.
    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.
    Linnarsson, M.K.
    Solid State Electronics, Royal Institute of Technology, P.O. Box E229, S-16440 Kista, Sweden.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Site-occupying behavior of boron in compensated p-type 4H-SiC grown by sublimation epitaxy2002In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 91, no 5, p. 3471-3473Article in journal (Refereed)
    Abstract [en]

    Results from electrical and optical measurements of boron in compensated p-type 4H-SiC layers doped with Al, N, and B are reported. The layers were produced by sublimation epitaxy and characterized by secondary ion mass spectrometry, capacitance-voltage, and cathodoluminescence techniques. The boron-related contribution to the net acceptor concentration in the layers as well as the boron-related emission at ~505 nm are detected for various growth conditions. The effect of the concentrations of the attendant impurities Al and N, concentration ratio of Al to N atoms, and growth rate on the site-occupying behavior of boron in the layers is discussed. © 2002 American Institute of Physics.

  • 114.
    Kakanakova-Georgieva, Anelia
    et al.
    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.
    Syväjärvi, Mikael
    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.
    Behavior of background impurities in thick 4H-SiC epitaxial layers2001In: Appl. Surf. Sci., Vol. 184, 2001, Vol. 184, no 1-4, p. 242-246Conference paper (Refereed)
    Abstract [en]

    Behavior of background impurities in 4H-SiC layers is studied in terms of several growth process parameters. The layers were produced by sublimation epitaxy in Ta and Hf, as well as in graphite growth cell environment. Cathodoluminescence imaging and spectroscopy of cleaved samples demonstrate the impurity - thickness uniformity along thick (40-260 µm) layers. The effect of the Ta and Hf environment on the levels of residual impurities is considered through calculations of cohesive energies of Ta-X and Hf-X diatomic molecules and comparing them with those obtained for N-, Al- and B-containing vapor molecules. © 2001 Elsevier Science B.V. All rights reserved.

  • 115.
    Kakanakova-Georgieva, Anelia
    et al.
    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.
    Zhang, J
    Storasta, Liutauras
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Syväjärvi, Mikael
    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.
    Characteristics of boron in 4H-SiC layers produced by high-temperature techniques2002In: Materials Science Forum, Vols. 389-393, 2002, Vol. 389-3, p. 259-262Conference paper (Refereed)
    Abstract [en]

    Characteristics of boron in as-grown 4H-SiC layers produced by fast epitaxy, i.e. sublimation and vertical hot-wall CVD, were studied by electrical and optical measurements. The boron-related contribution to the net acceptor concentration in the layers (as determined by CV on p-type residual doped sublimation epitaxy layers), the presence of deep boron centers (as indicated by DLTS) and boron-related "green" emission at similar to 505 nm (as observed by CL) are detected for various growth temperatures and C/Si ratios. The results are discussed in relation with the C vacancies in the lattice that may be affected by growth rate and input C/Si ratio in the CVD process.

  • 116. Kalabukhova, E.N.
    et al.
    Lukin, S.N.
    Savchenko, D.V.
    Mitchel, W.C.
    Greulich-Weber, S.
    Gerstmann, U.
    Pöppl, A.
    Hoentsch, J.
    Rauls, E.
    Rozentzveig, Y.
    Mokhov, E.N.
    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 .
    EPR, ESE and Pulsed ENDOR Study of Nitrogen Related Centers in 4H-SiC Wafers Grown by Different Technologies2007In: ECSCRM 2006,2006, Material Science Forum, vol. 556-557: Trans Tech Publications , 2007, p. 355-Conference paper (Refereed)
  • 117.
    Kamiyama, Satoshi
    et al.
    Department of Materials Science and Engineering, Meijo University, 1-501 Shiogamaguchi, Tenpaku-ku,.
    Iwaya, Motoaki
    Department of Materials Science and Engineering, Meijo University, 1-501 Shiogamaguchi, Tenpaku-ku,.
    Takeuchi, Tetsuya
    Department of Materials Science and Engineering, Meijo University, 1-501 Shiogamaguchi, Tenpaku-ku,.
    Akasaki, Isamu
    Department of Materials Science and Engineering, Meijo University, 1-501 Shiogamaguchi, Tenpaku-ku,.
    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.
    Fluorescent SiC and its application to white light-emitting diodes2011In: Journal of semiconductors, ISSN 1674-4926, Vol. 32, no 1, p. 013004-1-013004-3Article in journal (Refereed)
    Abstract [en]

    Fluorescent-SiC (f-SiC), which contains donor and acceptor impurities with optimum concentrations, has high conversion efficiency from NUV to visible light caused by donor-acceptor-pair (DAP) recombination. This material can be used as a substrate for a near UV light-emitting diode (LED) stack, and leads to monolithic white LED device with suitable spectral property for general lighting applications. In this paper, we describe basic technologies of the white LED, such as optical properties of f-SiC substrate, and epitaxial growth of NUV stack on the f-SiC substrate.

  • 118.
    Kamiyama, Satoshi
    et al.
    Meijo University, Japan .
    Iwaya, Motoaki
    Meijo University, Japan .
    Takeuchi, Tetsuya
    Meijo University, Japan .
    Akasaki, Isamu
    Meijo University, Japan .
    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.
    White light-emitting diode based on fluorescent SiC2012In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 522, p. 23-25Article in journal (Refereed)
    Abstract [en]

    A monolithic white light-emitting diode (LED,) comprising a combination of a fluorescent-SiC (f-SiC) substrate and a nitride-based near-UV LED stack, is proposed. On the basis of the recombination of donor and acceptor pairs, the f-SiC substrate works as a phosphor for visible light emission. By employing the Fast Sublimation Growth Process method, the high-quality f-SiC substrate doped with N and B exhibited a nonradiative carrier lifetime of 55 mu s and an internal quantum efficiency (IQE) of 40%. With increasing donor and acceptor doping concentrations, a high IQE was estimated even at a high excitation level.

  • 119.
    Karch, J
    et al.
    Terahertz Center, University of Regensburg, Germany.
    Drexler, C
    Terahertz Center, University of Regensburg, Germany.
    Olbrich, P
    Terahertz Center, University of Regensburg, Germany.
    Fehrenbacher, M
    Terahertz Center, University of Regensburg, Germany.
    Hirmer, M
    Terahertz Center, University of Regensburg, Germany.
    Glazov, M. M.
    Ioffe Physical-Technical Institute, Russian Academy of Sciences, St. Petersburg.
    Tarasenko, S. A.
    Ioffe Physical-Technical Institute, Russian Academy of Sciences, St. Petersburg.
    Ivchenko, E. L.
    Ioffe Physical-Technical Institute, Russian Academy of Sciences, St. Petersburg.
    Birkner, B
    Terahertz Center, University of Regensburg, Germany.
    Eroms, J
    Terahertz Center, University of Regensburg, Germany.
    Weiss, D
    Terahertz Center, University of Regensburg, Germany.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Lara-Avila, S
    Chalmers University of Technology.
    Kubatkin, S
    Chalmers University of Technology.
    Ostler, M
    University of Erlangen-Nürnberg, Germany.
    Seyller, T
    University of Erlangen-Nürnberg, Germany.
    Ganichev, S. D.
    Terahertz Center, University of Regensburg, Germany.
    Terahertz Radiation Driven Chiral Edge Currents in Graphene2011In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 107, no 27, p. 276601-1-276601-5Article in journal (Refereed)
    Abstract [en]

    We observe photocurrents induced in single-layer graphene samples by illumination of the graphene edges with circularly polarized terahertz radiation at normal incidence. The photocurrent flows along the sample edges and forms a vortex. Its winding direction reverses by switching the light helicity from left to right handed. We demonstrate that the photocurrent stems from the sample edges, which reduce the spatial symmetry and result in an asymmetric scattering of carriers driven by the radiation electric field. The developed theory based on Boltzmann’s kinetic equation is in a good agreement with the experiment. We show that the edge photocurrents can be applied for determination of the conductivity type and the momentum scattering time of the charge carriers in the graphene edge vicinity.

  • 120.
    Karch, J.
    et al.
    University of Regensburg.
    Olbrich, P.
    University of Regensburg.
    Schmalzbauer, M.
    University of Regensburg.
    Zoth, C.
    University of Regensburg.
    Brinsteiner, C.
    University of Regensburg.
    Fehrenbacher, M.
    University of Regensburg.
    Wurstbauer, U.
    University of Regensburg.
    Glazov, M.M.
    Russian Academy of Science.
    Tarasenko, S.A.
    Russian Academy of Science.
    Ivchenko, E.L.
    Russian Academy of Science.
    Weiss, D.
    University of Regensburg.
    Eroms, J.
    University of Regensburg.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Lara-Avila, S.
    Chalmers.
    Kubatkin, S.
    Chalmers.
    Ganichev, S.D.
    University of Regensburg.
    Dynamic Hall Effect Driven by Circularly Polarized Light in a Graphene Layer2010In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 105, no 22, p. 227402-Article in journal (Refereed)
    Abstract [en]

    We report the observation of the circular ac Hall effect where the current is solely driven by the crossed ac electric and magnetic fields of circularly polarized radiation. Illuminating an unbiased monolayer sheet of graphene with circularly polarized terahertz radiation at room temperature generates-under oblique incidence-an electric current perpendicular to the plane of incidence, whose sign is reversed by switching the radiation helicity. Alike the classical dc Hall effect, the voltage is caused by crossed E and B fields which are, however rotating with the lights frequency.

  • 121.
    Karlsson, Mikael
    et al.
    Department of Sensor System, Acreo Swedish ICT AB, Box 1070, SE-16440 Kista, Sweden; Department of Materials and Nano Physics, KTH-Royal Institute of Technology, Kista, Sweden .
    Wang, Qin
    Department of Sensor System, Acreo Swedish ICT AB, Box 1070, SE-16440 Kista, Sweden.
    Zhao, Yichen
    Department of Materials and Nano Physics, KTH-Royal Institute of Technology, Kista, Sweden.
    Zhao, Wei
    Department of Sensor System, Acreo Swedish ICT AB, Box 1070, SE-16440 Kista, Sweden; Department of Materials and Nano Physics, KTH-Royal Institute of Technology, Kista, Sweden.
    Toprak, Muhammet S.
    Department of Materials and Nano Physics, KTH-Royal Institute of Technology, Kista, Sweden.
    Iakimov, Tihomir
    Graphensic AB, Mjärdevi Science Park, Teknikringen 1F, SE-58330 Linköping, Sweden.
    Ali, Amer
    Graphensic AB, Mjärdevi Science Park, Teknikringen 1F, SE-58330 Linköping, Sweden.
    Yakimova, Rositsa
    Graphensic AB, Mjärdevi Science Park, Teknikringen 1F, SE-58330 Linköping, Sweden.
    Syväjärvi, Mikael
    Graphensic AB, Mjärdevi Science Park, Teknikringen 1F, SE-58330 Linköping, Sweden.
    Ivanov, Ivan G.
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Wafer-scale epitaxial graphene on SiC for sensing applications2015In: Micro+Nano Materials, Devices, and Systems / [ed] Benjamin J. Eggleton, Stefano Palomba, SPIE - International Society for Optical Engineering, 2015, Vol. 9668, p. 96685T-1-96685T-7Conference paper (Refereed)
    Abstract [en]

    The epitaxial graphene-on-silicon carbide (SiC-G) has advantages of high quality and large area coverage owing to a natural interface between graphene and SiC substrate with dimension up to 100 mm. It enables cost effective and reliable solutions for bridging the graphene-based sensors/devices from lab to industrial applications and commercialization. In this work, the structural, optical and electrical properties of wafer-scale graphene grown on 2’’ 4H semi-insulating (SI) SiC utilizing sublimation process were systemically investigated with focus on evaluation of the graphene’s uniformity across the wafer. As proof of concept, two types of glucose sensors based on SiC-G/Nafion/Glucose-oxidase (GOx) and SiC-G/Nafion/Chitosan/GOx were fabricated and their electrochemical properties were characterized by cyclic voltammetry (CV) measurements. In addition, a few similar glucose sensors based on graphene by chemical synthesis using modified Hummer’s method were also fabricated for comparison. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

  • 122.
    Karpyna, V A
    et al.
    NASU, Ukraine.
    Evtukh, A A
    NASU, Ukraine.
    Semenenko, M O
    NASU, Ukraine.
    Lazorenko, V I
    NASU, Ukraine.
    Lashkarev, G V
    NASU, Ukraine.
    Khranovskyy, Volodymyr
    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.
    Fedorchenko , D A
    NASU, Ukraine.
    Electron field emission from ZnO self-organized nanostructures and doped ZnO: Ga nanostructured films2009In: Microelectronics Journal, ISSN 0959-8324, Vol. 40, no 2, p. 229-231Article in journal (Refereed)
    Abstract [en]

    Self-organized ZnO nanostructures were grown by thermal decomposition of metalorganic precursors as well as by carbothermal reduction process. Nanostructured undoped and gallium-doped ZnO nanostructured films were deposited by plasma-enhanced chemical vapor deposition from metalorganic compounds. Electron field emission follows Fowler-Nordheim equation. Efficient electron emission was obtained from self-organized nanorstructures due to their geometric shape. Enhanced field emission from ZnO:Ga nanorstructured films in comparison with undoped ZnO films is obliged to lowering work function at doping by gallium.

  • 123. Kasamakova-Kolaklieva, L
    et al.
    Yakimova, Rositsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Kakanakov, R
    Kakanakova-Georgieva, Anelia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Syväjärvi, Mikael
    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.
    Characteristics of Ni Schottky contacts on compensated 4H-SiC layers2003In: Materials Science Forum, Vols. 433-436, Trans Tech Publications , 2003, Vol. 433-4, p. 709-712Conference paper (Refereed)
    Abstract [en]

    The electrical properties of Ni Schottky contacts to compensated 4H-SiC layers have been characterized by means of IN and C-V measurements and the key parameters have been determined. The measured barrier heights were between 0.90 eV and 2.90 eV depending on the conductivity type and the donor/acceptor concentration as well as the measurement techniques used. Inhomogeneties in IN characteristics of some rectifiers at lower forward-bias voltages have been observed. This may suggest enhanced trapping mechanism due to the nonuniform boron compensation of the epilayers.

  • 124.
    Kasic, A.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Gogova, Daniela
    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.
    Hemmingsson, Carl
    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, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Heuken, M.
    Aixtron AG, Germany .
    Characterization of crack-free relaxed GaN grown on 2″ sapphire2005In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 98, no 7, p. 73525-Article in journal (Refereed)
    Abstract [en]

    We demonstrate the growth of high-quality and virtually strain-free bulklike GaN by hydride vapor-phase epitaxy in a vertical atmospheric-pressure reactor with a bottom-fed design. The 300‐μm-thick GaN layer was grown on a 2″ (0 0 0 1) sapphire substrate buffered with a ∼ 2‐μm-thick GaN layer grown by metal-organic chemical-vapor deposition. During the cool down process to room temperature, cracking was induced in the sapphire substrate, thereby allowing the bulklike GaN layer to relax without provoking cracking of itself. The crystalline quality and the residual strain in the 2″ GaN wafer were investigated by various characterization techniques. The lateral homogeneity of the wafer was monitored by low-temperature photoluminescence mapping. High-resolution x-ray diffraction and photoluminescence measurements proved the high crystalline quality of the material grown. The position of the main near-band-gap photoluminescence line and the phonon spectra obtained from infrared spectroscopic ellipsometry show consistently that the 2″ crack-free GaN is virtually strain-free over a diameter of approximately 4 cm.

  • 125.
    Kassamakova, L
    et al.
    Bulgarian Acad Sci, Inst Appl Phys, BG-4000 Plovdiv, Bulgaria Linkoping Univ, Dept Phys & Measurement Technol, SE-58183 Linkoping, Sweden.
    Kakanakov, R
    Bulgarian Acad Sci, Inst Appl Phys, BG-4000 Plovdiv, Bulgaria Linkoping Univ, Dept Phys & Measurement Technol, SE-58183 Linkoping, Sweden.
    Yakimova, Rositsa
    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.
    Syväjärvi, Mikael
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Wilzén, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Effect of temperature treatment on Au/Pd Schottky contacts to 4H-SiC2002In: Materials Science Forum, Vols. 389-393, 2002, Vol. 389-3, p. 929-932Conference paper (Refereed)
    Abstract [en]

    Au/Pd/SiC Schottky baffler contacts have been formed on n-type 4H-SiC grown by sublimation epitaxy. The effect of annealing temperature on the electrical properties of these contacts was studied using IN and C-V measurements. The barrier height was found to increase slightly from 1.14 eV for as-deposited contacts to 1.2 eV after annealing at 500 degreesC, while the more pronounced effect was observed with decrease of the ideality factor, Auger analysis was used to study the metallurgy of the annealed contacts. Strong diffusion between Au and Pd was established after 500 degreesC anneal, while the Pd/SiC interface remained almost steep, The electrical properties of annealed contacts have been study during the thermal treatment at temperatures up to 350 degreesC and prolonged ageing at 300 degreesC and 400 degreesC in nitrogen.

  • 126.
    Kayambaki, M.
    et al.
    Found. for Res. and Technol.-Hellas, Heraklion, Crete 71110, Greece.
    Tsagaraki, K.
    Found. for Res. and Technol.-Hellas, Heraklion, Crete 71110, Greece.
    Cimalla, V.
    Found. for Res. and Technol.-Hellas, Heraklion, Crete 71110, Greece.
    Zekentes, K.
    Found. for Res. and Technol.-Hellas, Heraklion, Crete 71110, Greece.
    Yakimova, Rositsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Crystal quality evaluation by electrochemical preferential etching of p-type SiC crystals2000In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 147, no 7, p. 2744-2748Article in journal (Refereed)
    Abstract [en]

    An electrochemical etching process is used for evaluating the types and the distribution of crystal defects on both the Si and C faces of p-type 6H and 4H-SiC. The surface morphology of the etched area is different for the two surface polarities. Dislocation-related etch-pits appeared on the etched surfaces due to a preferential etching process. The etching experiments were conducted in a commercial apparatus in combination with accurate capacitance-voltage profiling, showing that this characterization method is highly useful and simple for evaluating SiC material quality.

  • 127.
    Kayambaki, M
    et al.
    Fdn Res & Technol Hellas, Microelect Res Grp, IESL, GR-71110 Iraklion, Greece INPG, ENSPG, UMR CNRS 5628, Mat & Genie Phys Lab, FR-38402 St Martin Dheres, France Linkoping Univ, Dept Phys & Measurement Technol, SE-58183 Linkoping, Sweden.
    Zekentes, K
    Fdn Res & Technol Hellas, Microelect Res Grp, IESL, GR-71110 Iraklion, Greece INPG, ENSPG, UMR CNRS 5628, Mat & Genie Phys Lab, FR-38402 St Martin Dheres, France Linkoping Univ, Dept Phys & Measurement Technol, SE-58183 Linkoping, Sweden.
    Tsagaraki, K
    Fdn Res & Technol Hellas, Microelect Res Grp, IESL, GR-71110 Iraklion, Greece INPG, ENSPG, UMR CNRS 5628, Mat & Genie Phys Lab, FR-38402 St Martin Dheres, France Linkoping Univ, Dept Phys & Measurement Technol, SE-58183 Linkoping, Sweden.
    Pernot, E
    Fdn Res & Technol Hellas, Microelect Res Grp, IESL, GR-71110 Iraklion, Greece INPG, ENSPG, UMR CNRS 5628, Mat & Genie Phys Lab, FR-38402 St Martin Dheres, France Linkoping Univ, Dept Phys & Measurement Technol, SE-58183 Linkoping, Sweden.
    Yakimova, Rositsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Electrochemical characterization of p-type hexagonal SiC2001In: Materials Science Forum, Vols. 353-356, 2001, Vol. 353-3, p. 619-622Conference paper (Refereed)
    Abstract [en]

    Electrochemical etching experiments in combination with C-V measurements: of 6H and 4H-SiC p-type material can be used to determine the doping profile and the evaluation of the types and distribution of crystal defects. Dislocation-related etch-l,its appeared on the etched surfaces due to a preferential etching process. Doping profiles were obtained for etched depths down to 84 mum. The experiments were conducted in a simple commercial apparatus and the reproducibility of the method was demonstrated.

  • 128.
    Kazakova, O
    et al.
    National Phys Lab, England .
    Burnett, T L.
    National Phys Lab, England .
    Patten, J
    National Phys Lab, England .
    Yang, L
    National Phys Lab, England .
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Epitaxial graphene on SiC(000(1)over-bar): functional electrical microscopy studies and effect of atmosphere2013In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 24, no 21Article in journal (Refereed)
    Abstract [en]

    Surface potential distribution, V-CPD, and evolution of atmospheric adsorbates on few and multiple layers (FLG and MLG) of graphene grown on SiC(000 (1) over bar) substrate have been investigated by electrostatic and Kelvin force microscopy techniques at T = 20-120 degrees C. The change of the surface potential distribution, Delta V-CPD, between FLG and MLG is shown to be temperature dependent. The enhanced Delta V-CPD value at 120 degrees C is associated with desorption of adsorbates at high temperatures and the corresponding change of the carrier balance. The nature of the adsorbates and their evolution with temperature are considered to be related to the process of adsorption and desorption of the atmospheric water on MLG domains. We demonstrate that both the nano- and microscale wettability of the material are strongly dependent on the number of graphene layers.

  • 129.
    Khomyak, V.
    et al.
    Fedkovich Chernivtsi National University, Ukraine.
    Shtepliuk, I.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. NAS Ukraine, Ukraine.
    Khranovskyy, Volodymyr
    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.
    Band-gap engineering of ZnO1-xSx films grown by rf magnetron sputtering of ZnS target2015In: Vacuum, ISSN 0042-207X, E-ISSN 1879-2715, Vol. 121, p. 120-124Article in journal (Refereed)
    Abstract [en]

    Structural and optical properties of ZnO1-xSx (0 less than= x less than= 1.0) thin films grown onto sapphire substrates (c-Al2O3) at 300 degrees C by radio frequency (rf) magnetron sputtering of ZnS ceramic target are studied. A possibility of purposeful controlling sulfur content and, as consequence, ZnO1-xSx band gap energy via changing the ratio of the partial pressures of argon and oxygen are revealed. Linear dependence of ZnO lattice parameter c on S content suggests that structural properties of single-phase ternary alloys in the composition range between ZnO and ZnS obey Vegards law. The mechanisms of influence of gas mixing ratio on film growth and band gap energy are discussed. Cu(In,Ga)Se-2 (CIGS)-based heterojunction solar cells with ZnO1-xSx buffer layers were fabricated by one-cycle magnetron sputtering procedure. Electrical characteristics of Cd-free devices are comparable to those of CdS-containing photovoltaic heterostructures, thereby indicating prospects of using ZnO1-xSx layers for fabrication of CIGS solar cells. (C) 2015 Elsevier Ltd. All rights reserved.

  • 130. Khranovskyy, V.
    et al.
    Grossner, U.
    Kopylova, L.I.
    Lazorenko, V.
    Budnikov, A.T.
    Lashkarev, G.V.
    Svensson, B.G.
    Yakimova, Rositsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Conductivity increase of ZnO: Ga films by rapid thermal annealing2007In: Superlattices and Microstructures, ISSN 0749-6036, E-ISSN 1096-3677, Vol. 42, no 1-6, p. 379-386Article in journal (Refereed)
    Abstract [en]

    Due to a constant increase in demands for transparent electronic devices the search for alternative transparent conducting oxides (TCO) is a major field of research now. New materials should be low-cost and have comparable or better optical and electrical characteristics in comparison to ITO. The use of n-type ZnO was proposed many years ago, but until now the best n-type dopant and its optimal concentration is still under discussion. Ga was proposed as the best dopant for ZnO due to similar atomic radius of Ga3+ compared to Zn2+ and its lower reactivity with oxygen. The resistivity ρ of ZnO:Ga/Si (100) films grown by PEMOCVD was found to be 3×10-2 Ω cm. Rapid thermal annealing (RTA) was applied to increase the conductivity of ZnO:Ga (1 wt%) films and the optimal regime was determined to be 800  {ring operator}C in oxygen media for 35 s. The resistivity ratio ρbefore / ρafter before and after the annealing and the corresponding surface morphologies were investigated. The resistivity reduction (ρbefore / ρafter ≈ 80) was observed after annealing at optimal regime and the final film resistivity was approximately ≈4×10-4 Ω cm, due to effective Ga dopant activation. The route mean square roughness (Rq) of the films was found to decrease with increasing annealing time and the grain size has been found to increase slightly for all annealed samples. These results allow us to prove that highly conductive ZnO films can be obtained by simple post-growth RTA in oxygen using only 1% of Ga precursor in the precursor mix. © 2007 Elsevier Ltd. All rights reserved.

  • 131. Khranovskyy, V.
    et al.
    Grossner, U.
    Lashkarev, G.V.
    Svensson, B.G.
    Yakimova, Rositsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    PEMOCVD of ZnO thin films, doped by Ga and some of their properties2006In: Superlattices and Microstructures, ISSN 0749-6036, E-ISSN 1096-3677, Vol. 39, no 1-4, p. 275-281Article in journal (Refereed)
    Abstract [en]

    Zinc oxide (ZnO) is a promising semiconductor material with a great variety of applications, for example for highly conductive films for transparent electronics. Recently, Ga has been proposed as a dopant, exhibiting the advantages of a very similar atomic radius compared to Zn, a smaller reactivity, and a higher resistivity to oxidation compared to its competitor Al. In this study ZnO films, doped by Ga, were produced on Al2O3(0001) substrates by PEMOCVD. The doping was realized with 1, 3, 5 and 10 wt% gallium precursor content in the mixture. The resistivity of the prepared films, as well as the morphology and the transmittance, was investigated. All the deposited films have demonstrated a high optical transmittance above 93% in the range between 400 and 800 nm. A strong correlation between the electrical resistivity and the optical band gap depending on the Ga content was observed. An AFM analysis demonstrated highly uniform and smooth surfaces. The average grain size and route mean square roughness decreased with increasing Ga content. © 2005 Elsevier Ltd. All rights reserved.

  • 132. Khranovskyy, V.
    et al.
    Grossner, U.
    Lazorenko, V.
    Lashkarev, G.
    Svensson, B.G.
    Yakimova, Rositsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Study of annealing influence on electrical and morphological properties of ZnO: Ga thin films2006In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 3, no 4, p. 780784-Article in journal (Refereed)
  • 133.
    Khranovskyy, V.
    et al.
    Institute for Problems of Material Science, Krzhyzhanovskyy str. 3, 03142 Kiev, Ukraine, University of Oslo, Physics Department, Centre for Materials Science and Nanotechnology, N-0316 Oslo, Norway.
    Grossner, U.
    University of Oslo, Physics Department, Centre for Materials Science and Nanotechnology, N-0316 Oslo, Norway.
    Nilsen, O.
    University of Oslo, Chemistry Department, Centre for Materials Science and Nanotechnology, N-0316 Oslo, Norway.
    Lazorenko, V.
    Institute for Problems of Material Science, Krzhyzhanovskyy str. 3, 03142 Kiev, Ukraine.
    Lashkarev, G.V.
    Institute for Problems of Material Science, Krzhyzhanovskyy str. 3, 03142 Kiev, Ukraine.
    Svensson, B.G.
    University of Oslo, Physics Department, Centre for Materials Science and Nanotechnology, N-0316 Oslo, Norway.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Structural and morphological properties of ZnO: Ga thin films2006In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 515, no 2 SPEC. ISS., p. 472-476Article in journal (Refereed)
    Abstract [en]

    Zinc oxide (ZnO) is a promising semiconductor material with a great variety of applications. Compared to undoped ZnO, impurity-doped ZnO has a lower resistivity and better stability. With this aim, Ga has been proposed as a dopant. In this study, the structural characteristics and surface morphology of ZnO films produced by PEMOCVD at a substrate temperature of 250 °C on the c-plane (001) of sapphire were investigated. Doping was realized with 1, 3, 5 and 10 wt.% of Ga2(AA)3 in the precursor's mixture. At lower contents, Ga stimulates growth of (002) oriented textured films and the smallest FWHM was obtained as low as 0.17° for ZnO:Ga with 1 wt.%. A change in preferential orientation as well as surface smoothing and roughness decreasing of the films were observed with further increasing Ga content in precursor's mixture. We assume a key role of Ga and note that such a feature would be beneficial for the application of ZnO thin films for formation of abrupt junctions in p-n device structures. © 2005 Elsevier B.V. All rights reserved.

  • 134.
    Khranovskyy, V.
    et al.
    Institute for Problems of Material Science, Krzhyzhanovskyy Str. 3, 03630 Kyiv, Ukraine, Linkoping University, Department of Physics, Chemistry and Biology, SE-58183 Linkoping, Sweden.
    Minikayev, R.
    Institute of Physics, P.A.S., Al. Lotników 32/46, 02-668 Warsaw, Poland.
    Trushkin, S.
    Institute of Physics, P.A.S., Al. Lotników 32/46, 02-668 Warsaw, Poland.
    Lashkarev, G.
    Institute for Problems of Material Science, Krzhyzhanovskyy Str. 3, 03630 Kyiv, Ukraine.
    Lazorenko, V.
    Institute for Problems of Material Science, Krzhyzhanovskyy Str. 3, 03630 Kyiv, Ukraine.
    Grossner, U.
    University of Oslo, Physics Department, Centre for Materials Science and Nanotechnology, N-0316 Oslo, Norway.
    Paszkowicz, W.
    Institute of Physics, P.A.S., Al. Lotników 32/46, 02-668 Warsaw, Poland.
    Suchocki, A.
    Institute of Physics, P.A.S., Al. Lotników 32/46, 02-668 Warsaw, Poland.
    Svensson, B.G.
    University of Oslo, Physics Department, Centre for Materials Science and Nanotechnology, N-0316 Oslo, Norway.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Improvement of ZnO thin film properties by application of ZnO buffer layers2007In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 308, no 1, p. 93-98Article in journal (Refereed)
    Abstract [en]

    The effect of ZnO buffer layers prepared at different temperatures on the structural, optical and morphological properties of the ZnO main layer is reported. ZnO thin films (comprising a buffer and a main layer) were deposited on (0 0 0 1) c-sapphire substrates by PEMOCVD. Two-step growth regimes were applied to realize a homoepitaxial growth on ZnO buffers: low-temperature ZnO buffer layer deposited at Ts=300 °C and the main layer at Ts=500 °C, high-temperature ZnO buffer layer deposited at Ts=500 °C and the main layer at Ts=300 °C. For comparison, a sample grown at high-temperature Ts=500 °C by one-step procedure was used. The low-temperature buffer layer has shown the most beneficial effect on the structural and morphological properties, as expressed by the narrowing of the (0 0 2) diffraction peak (FWHM=0.07°) and crystallite size enlargement. However, the surface roughness of this sample is higher then that of the sample grown by one-step procedure and this needs further considerations. The photoluminescence results seem to support a conclusion that the application of a low-temperature buffer layer among the studied temperature regimes is the most advantageous. © 2007 Elsevier B.V. All rights reserved.

  • 135. Khranovskyy, V
    et al.
    Tsiaoussis, I
    Syväjärvi, Mikael
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Larsson, Arvid
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Holtz, Per-Olof
    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 .
    Size tuning of uniformly oriented ZnO nanostructures2008In: Nanotech 2008,2008, 2008Conference paper (Refereed)
  • 136.
    Khranovskyy, V.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ulyashin, A.
    University of Oslo, Physics Department, Centre for Materials Science and Nanotechnology, N-0316 Oslo, Norway.
    Lashkarev, G.
    Institute for Problems of Material Science, Krzhyzhanovskyy str. 3, 03680 Kiev, Ukraine.
    Svensson, B.G.
    University of Oslo, Physics Department, Centre for Materials Science and Nanotechnology, N-0316 Oslo, Norway.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Morphology, electrical and optical properties of undoped ZnO layers deposited on silicon substrates by PEMOCVD2008In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 516, no 7, p. 1396-1400Article in journal (Refereed)
    Abstract [en]

    The goal of this work is to investigate the morphology, electrical and optical properties of undoped ZnO (i-ZnO) thin layers deposited on Si substrates with (100) and (111) orientations. Plasma enhanced metalorganic chemical vapor deposition (PEMOCVD) was used for the deposition of i-ZnO layers at different temperatures. Atomic force microscopy (AFM), ellipsometry and four-probe method were used for the analysis. It is found that substrate orientation and growth temperature determine the morphological (grains size, surface roughness) as well as electrical properties of ZnO films. It is shown that the refractive index value depends on the surface morphology. It is concluded that properties of i-ZnO layers deposited on different Si substrates at different conditions exhibit some trends and peculiarities, which have to be taken into account for the processing of heterojunction solar cells by the PEMOCVD method. © 2007 Elsevier B.V. All rights reserved.

  • 137.
    Khranovskyy, Volodymyr
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ekblad, Tobias
    Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular 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.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Surface morphology effects on the light-controlled wettability of ZnO nanostructures2012In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 258, no 20, p. 8146-8152Article in journal (Refereed)
    Abstract [en]

    ZnO nanostructures of diverse morphology with shapes of corrals and cabbages as well as open and filled hexagons and sheaves prepared by APMOCVD technique, are investigated with water contact angle (CA) analysis. The as-grown ZnO nanostructures exhibit pure hydrophobic behavior, which is enhanced with the increase of the nanostructures surface area. The most hydrophobic structures (CA = 124 degrees) were found to be the complex nanosheaf, containing both the macro-and nanoscale features. It is concluded that the nanoscale roughness contributes significantly to the hydrophobicity increase. The character of wettability was possible to switch from hydrophobic-to-superhydrophilic state upon ultra violet irradiation. Both the rate and amplitude of the contact angle depend on the characteristic size of nanostructure. The observed effect is explained due to the semiconductor properties of zinc oxide enhanced by increased surface chemistry effect in nanostructures.

  • 138.
    Khranovskyy, Volodymyr
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Eriksson, Jens
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Lloyd Spetz, 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.
    Oxygen absorption effect on the sensitivity and material stability of ZnO nanostructured films2008In: Proceedings of IEEE Sensors, IEEE , 2008, p. 874-877Conference paper (Refereed)
    Abstract [en]

    In this work the effect of ambient influence on the electrical conductivity of ZnO films has been studied. Nanostructured ZnO films (undoped and Ga, Co, Mn doped) were exposed to oxygen (1-80 vol.%) at temperature range 300-500degC. A dominant effect of ambient influence via oxygen absorption was observed: the intensity of conductivity decrease was found to be proportional with temperature and tends to saturation with time. After oxygen saturation the reversible effect of oxygen adsorption became dominant and contributed to the films conductivity. Oxygen exposed undoped ZnO films revealed high sensitivity for oxygen content change in the ambience, therefore they have been further processed for gas sensor fabrication.

  • 139.
    Khranovskyy, Volodymyr
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Eriksson, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, The Institute of Technology.
    Lloyd Spetz, Anita
    Linköping University, Department of Physics, Chemistry and Biology, Applied 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.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Effect of oxygen exposure on the electrical conductivity and gas sensitivity of nanostructured ZnO films2009In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 517, no 6, p. 2073-2078Article in journal (Refereed)
    Abstract [en]

    Nanostructured ZnO films (Undoped and Ga, Co, Mn doped) were exposed to oxygen (1-80 vol.%) at temperature range of 300-500 degrees C in order to reveal the ambience-temperature effect oil the electrical conductivity. The dominant effect of ambient influence via oxygen absorption was observed: the intensity of conductivity decrease was found to be proportional with temperature and tends to saturate with time. It is demonstrated that oxygen absorption occurs accordingly to diffusion law and the quantifying of oxygen diffusion was realized for different samples. It is revealed that the type of dopant affects the diffusion in ZnO and the tendency to increase the diffusion intensity with dopant content has been observed. After oxygen saturation the reversible effect of oxygen adsorption became dominant and contributed to the films conductivity. Oxygen exposure undoped ZnO films revealed high sensitivity for oxygen content change in the ambience therefore they have been preceded further for gas sensor design and the detailed investigation of films sensing properties has been carried out.

  • 140.
    Khranovskyy, Volodymyr
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Eriksson, Martin O.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Radnóczi, György Zoltán
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Khalid, Abbas
    University of Dublin Trinity Coll, Ireland.
    Zhang, Hongzhou
    University of Dublin Trinity Coll, Ireland.
    Holtz, Per-Olof
    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.
    Correction: Photoluminescence study of basal plane stacking faults in ZnO nanowires (vol 4639, pg 50, 2014)2014In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 454, p. 279-279Article in journal (Other academic)
    Abstract [en]

    n/a

  • 141.
    Khranovskyy, Volodymyr
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Eriksson, M.O.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Zoltán Radnóczi, György
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Khalid, A.
    University of Dublin Trinity Coll, Ireland University of Dublin Trinity Coll, Ireland .
    Zhang, H.
    University of Dublin Trinity Coll, Ireland University of Dublin Trinity Coll, Ireland .
    Holtz, Per-Olof
    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.
    Photoluminescence study of basal plane stacking faults in ZnO nanowires2014In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 439, p. 50-53Article in journal (Refereed)
    Abstract [en]

    We have investigated the photoluminescence (PL) of ZnO nanowires (NWs) containing a high density (similar to 1 x 10(6) cm(-1)) of basal plane stacking faults (BSFs). It was observed that the BSFs result in a specific PL peak at similar to 3.329 eV along with a donor bound excitonic emission (D degrees X) peak at 5 K. The observed BSF-related emission is of excitonic type and possesses longer PL lifetime than D degrees X (similar to 360 ps vs. similar to 70 ps). Via comparison of the microstructural and the PL properties of the ZnO NWs, it is shown that the observed BSF-related emission is due to the formation of crystal phase quantum wells (QWs). This is explained by the fact that BSF in wurtzite (WZ) ZnO is the thinnest segment of zinc blende (ZB) phase ZnO inserted in the WZ matrix, resulting in band alignment of type II due to the conduction and valence band offsets of ZB with respect to WZ ZnO. The mechanism of the BSF related PL is suggested to be an indirect exciton transitions clue to the recombination of electrons confined in the ZB QWs to holes in the WZ barriers localized near the BSFs.

  • 142.
    Khranovskyy, Volodymyr
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Glushenkov, Alexey M.
    Deakin University, Australia .
    Chen, Y
    Deakin University, Australia .
    Khalid, A
    Trinity Coll Dublin, Ireland .
    Zhang, H
    Trinity Coll Dublin, Ireland .
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Monemar, Bo
    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.
    Crystal phase engineered quantum wells in ZnO nanowires2013In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 24, no 21Article in journal (Refereed)
    Abstract [en]

    We report the fabrication of quantum wells in ZnO nanowires (NWs) by a crystal phase engineering approach. Basal plane stacking faults (BSFs) in the wurtzite structure can be considered as a minimal segment of zinc blende. Due to the existing band offsets at the wurtzite (WZ)/zinc blende (ZB) material interface, incorporation of a high density of BSFs into ZnO NWs results in type II band alignment. Thus, the BSF structure acts as a quantum well for electrons and a potential barrier for holes in the valence band. We have studied the photoluminescence properties of ZnO NWs containing high concentrations of BSFs in comparison to high-quality ZnO NWs of pure wurtzite structure. It is revealed that BSFs form quantum wells in WZ ZnO nanowires, providing an additional luminescence peak at 3.329 eV at 4 K. The luminescence mechanism is explained as an indirect exciton transition due to the recombination of electrons in the QW conduction band with holes localized near the BSF. The binding energy of electrons is found to be around 100 meV, while the excitons are localized with the binding energy of holes of ~5 meV, due to the coupling of BSFs, which form QW-like structures.

  • 143.
    Khranovskyy, Volodymyr
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Lashkarev, G
    Lazorenko, V
    Eriksson, Jens
    Lloyd Spetz, 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 .
    Investigation of oxygen exposure effect on electrical properties of ZnO based nanostructures films - a premise for sensor design2008In: Sensors electronics and Microsystem Technology Conference,2008, 2008Conference paper (Refereed)
    Abstract [en]

          

  • 144.
    Khranovskyy, Volodymyr
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Lazorenko, V
    Institute Problems Mat Science, Ukraine .
    Lashkarev, G
    Institute Problems Mat Science, Ukraine .
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Luminescence anisotropy of ZnO microrods2012In: Journal of Luminescence, ISSN 0022-2313, E-ISSN 1872-7883, Vol. 132, no 10, p. 2643-2647Article in journal (Refereed)
    Abstract [en]

    The local features of light emission from ZnO microrods were studied: it is revealed that ZnO luminescence spectra are significantly influenced by the crystal morphology. It is shown that the near and edge ultraviolet emission occurs primarily from the top (0001) planes of ZnO microrods; while the defect related visible emission was found to occur dominantly from the side facets. The room temperature cathodoluminescence analysis revealed that visible emission consists of a few overlapping peaks, arising due to recombination on common points and surface defects (Zn-i, V-o, V-o(O)/V-o(**) V-o(**) and surface defects.). While at low temperature, only the luminescence due to neutral donor bound exciton ((DX)-X-0) emission is observed. The data obtained suggest that the light emission spectra of ZnO material of diverse morphology cannot be directly compared, although some common spectral features are present.

  • 145.
    Khranovskyy, Volodymyr
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Shtepliuk, Ivan
    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.
    Tsiaoussis, I.
    Aristotle University of Thessaloniki, Thessaloniki, Greece.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Light emission enhancement from ZnO nanostructured films grown on Gr/SiC substrates2016In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 99, p. 295-301Article in journal (Refereed)
    Abstract [en]

    We report on the application of a single layer graphene substrates for the growth of polycrystalline ZnO films with advanced light emission properties. Unusually high ultraviolet (UV) and visible (VIS) photoluminesce was observed from the ZnO/Gr/SiC structures in comparison to identical samples without graphene. The photoluminescence intensity depends non-monotonically on the films thickness, reaching its maximum for 150 nm thick films. The phenomena observed is explained as due to the dual graphene role: i) the dangling bond free substrate, providing growth of relaxed thin ZnO layers ii) a back reflector active mirror of the Fabry-Perot cavity that is formed. The reported results demonstrate the potential of two-dimensional carbon materials integration with light emitting wide band gap semiconductors and can be of practical importance for the design of future optoelectronic devices.

  • 146.
    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.
    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.
    Selective homoepitaxial growth and luminescent properties of ZnO nanopillars2011In: NANOTECHNOLOGY, ISSN 0957-4484, Vol. 22, no 18, p. 185603-Article in journal (Refereed)
    Abstract [en]

    High spatial density ZnO nanopillars (NPs) have been fabricated on catalyst-and pattern-free Si wafers using atmospheric pressure metal organic chemical vapor deposition (APMOCVD) at a moderate temperature (500 degrees C). The nanopillar diameter is similar to 35 nm and the length is similar to 150 nm, with a density of similar to 2 x 10(9) cm(-2). The growth evolution of the nanopillars, providing the (0001)(NP) parallel to (0001)(ZnO) (grain) parallel to (100)(Si) (surface) epitaxial relationship, is extensively studied by scanning and high resolution transmission microscopy. The approach to obtaining the ZnO 1D structures is explained in terms of selective homoepitaxial growth via the crystallographic anisotropy of the seeding layer. The advanced PL properties of ZnO NPs, e. g. indications of free excitonic and absence of defect emission, are related to their single crystalline nature within one pillar and most probably better stoichiometry and less contamination. The observed efficient monochromatic UV emission from the ZnO NPs at room temperature points toward their potential application as building blocks for nanoscale optoelectronic devices.

  • 147.
    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, GR-54006 Thessaloniki, Greece .
    Larsson, Arvid
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Holtz, Per-Olof
    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.
    Nanointegration of ZnO with Si and SiC2009In: PHYSICA B-CONDENSED MATTER, ISSN 0921-4526, Vol. 404, no 22, p. 4359-4363Article in journal (Refereed)
    Abstract [en]

    The study is dedicated to some aspects of the controlled heteroepitaxial growth of nanoscaled ZnO structures and an investigation of their general and dimension mediated properties. ZnO nanostructures were synthesized by optimized MOCVD process via two growth approaches: (i) catalyst free self-organized growth of ZnO on Si substrates and (ii) ZnO heteroepitaxy on p-type hexagonal 4H-SiC substrates. The SiC substrate was prepared by sublimation epitaxy and served as a template for the ZnO epitaxial growth. The epitaxial growth of n-ZnO on p-SiC resulted in a regular matrix of well-faceted hexagonally shaped ZnO single crystals. The achievement of ZnO integration with Si encompasses controlled growth of vertically oriented nanosized ZnO pillars. The grown structures were characterized by transmission electron microscopy and microphotoluminescence. Low concentration of native defects due to a stoichiometry balance, advanced optical emission, (excitonic type near-band-edge emission and negligible defect related luminescence) and continuous interfaces (epitaxial relationship ZnO[0 0 0 1]/ SiC[0 0 0 1]) are evidenced. The ZnO nanopillars were further probed as field emitters: the grown structures exhibits advanced field emission properties, which are explained in term of dimensionality and spatial uniformity of the nanopillars. The present results contribute to understanding and resolving growth and device related issues of ZnO as a functional nanostructured material.

  • 148.
    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.

  • 149.
    Khranovskyy, Volodymyr
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Tsiaoussis, Ioannis
    Aristotle University of Thessaloniki, Greece.
    Eriksson, Martin
    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.
    Effect of Ag doping on the microstructure and photoluminescence of ZnO nanostructures2014In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 211, no 9, p. 2109-2114Article in journal (Refereed)
    Abstract [en]

    ZnO nanostructures were obtained by metal-organic chemical vapor deposition via Ag catalyst-assisted growth in a temperature range of 200-500 degrees C. Growth at temperatures above 500 degrees C resulted in vertically aligned ZnO nanorods (NLs). Ag incorporation into ZnO up to 0.4 at.% promoted creation of basal plane stacking fault (BSF) defects and corrugation of the side facets of the NLs. The presence of BSFs give rise to an additional photoluminescence peak with a wavelength of similar to 386 nm, which is slightly red-shifted compared to the commonly observed NBE emission at similar to 375 nm. The observed emission was found to be specifically observed from the side facets of the NLs. It is suggested that this emission is due to a high concentration of BSFs in the ZnO as a result of an incorporation of Ag as acceptor dopant. [GRAPHICS] SEM image of an Ag-doped ZnO nanorod with corrugated side facets. The observed corrugation is accompanied by a high concentration of basal plane stacking faults.

  • 150.
    Khranovskyy, Volodymyr
    et al.
    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.
    Morphology engineering of ZnO nanostructures2012In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 407, no 10, p. 1533-1537Article in journal (Refereed)
    Abstract [en]

    Nanosized ZnO structures were grown by atmospheric pressure metalorganic chemical vapor deposition (APMOCVD) in the temperature range 200-500 degrees C at variable precursor pressure. Temperature induced evolution of the ZnO microstructure was observed, resulting in regular transformation of the material from conventional polycrystalline layers to hierarchically arranged sheaves of ZnO nanowires. The structures obtained were uniformly planarly located over the substrate and possessed as low nanowires diameter as 30-45 nm at the tips. The observed growth evolution is explained in terms of ZnO crystal planes free energy difference and growth kinetics. For comparison, the convenient growth at constant precursor pressure on Si and SiC substrates has been performed, resulting in island-type grown ZnO nanostructures. The demonstrated nanosized ZnO structures may have unique possible areas of application, which are listed here.

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