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  • 101.
    Monemar, Bo
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Paskova, Tanja
    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.
    Larsson, Henrik
    IFM Linköpings universitet.
    Paskov, Plamen
    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.
    Kasic, Aleksander
    Growth of thick GaN layers by hydride vapor phase epitaxy2005In: Journal of Ceramic Processing Research, ISSN 1229-9162, Vol. 6, no 2, p. 153-162Article in journal (Refereed)
    Abstract [en]

    In this paper we describe recent experimental work on the growth of thick GaN layers (up to >300 μm) on sapphire with hydride vapour phase epitaxy (HVPE), the removal of the sapphire substrate by the laser liftoff technique, and the properties of these thick GaN layers. Two different growth setups were used, one horizontal and one vertical system. Specific conditions in the growth procedure, like gas flow pattern, growth rate and the use of buffer layers, strongly influence the properties of the grown layers. Important defect problems are cracking (both during and after growth), and the generation of dislocations and surface pits. A large bowing is also observed for thick layers, depending very much on the properties of the initially grown material. For growth of thick layers excessive parasitic growth of GaN upstream of the substrate has to be avoided. Laser liftoff is demonstrated to be a feasible process to remove the sapphire substrate, causing the GaN surface bowing to decrease and revert from convex to concave. The threading dislocation density of 300 μm thick GaN layers is found to be about 107 cm-2, rather independent of the type of buffer layer employed. It reduces further in thicker layers. The pit density varies with growth conditions, it can be reduced if the parasitic growth is avoided. The bowing is a serious problem, since the layers have to be polished to make the surface epi-ready. The XRD rocking curve widths measured seem to correlate with the bowing of the layers, a reduction by about a factor two is often observed when the substrate is removed. Optical characterisation like photoluminescence (PL) and ir spectroscopic ellipsometry (IRSE) is very useful to monitor strain in the layers, as well as impurities and point defects. Residual shallow donors are related to O and Si, shallow acceptors are mainly of intrinsic origin, i.e. complexes with the Ga vacancy.

  • 102.
    Nagy, Roland
    et al.
    Univ Stuttgart, Germany; Inst Quantum Sci and Technol, Germany.
    Niethammer, Matthias
    Univ Stuttgart, Germany; Inst Quantum Sci and Technol, Germany.
    Widmann, Matthias
    Univ Stuttgart, Germany; Inst Quantum Sci and Technol, Germany.
    Chen, Yu-Chen
    Univ Stuttgart, Germany; Inst Quantum Sci and Technol, Germany.
    Udvarhelyi, Peter
    Hungarian Acad Sci, Hungary; Eotvos Lorand Univ, Hungary.
    Bonato, Cristian
    Heriot Watt Univ, Scotland.
    Ul-Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Karhu, Robin
    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.
    Nguyen, Son Tien
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Maze, Jeronimo R.
    Pontificia Univ Catolica Chile, Chile; Pontificia Univ Catolica Chile, Chile.
    Ohshima, Takeshi
    Natl Inst Quantum and Radiol Sci and Technol, Japan.
    Soykal, Oney O.
    Naval Res Lab, DC 20375 USA.
    Gali, Adam
    Hungarian Acad Sci, Hungary; Budapest Univ Technol and Econ, Hungary.
    Lee, Sang-Yun
    Korea Inst Sci and Technol, South Korea.
    Kaiser, Florian
    Univ Stuttgart, Germany; Inst Quantum Sci and Technol, Germany.
    Wrachtrup, Joerg
    Univ Stuttgart, Germany; Inst Quantum Sci and Technol, Germany.
    High-fidelity spin and optical control of single silicon-vacancy centres in silicon carbide2019In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 10, article id 1954Article in journal (Refereed)
    Abstract [en]

    Scalable quantum networking requires quantum systems with quantum processing capabilities. Solid state spin systems with reliable spin-optical interfaces are a leading hardware in this regard. However, available systems suffer from large electron-phonon interaction or fast spin dephasing. Here, we demonstrate that the negatively charged silicon-vacancy centre in silicon carbide is immune to both drawbacks. Thanks to its (4)A(2) symmetry in ground and excited states, optical resonances are stable with near-Fourier-transform-limited linewidths, allowing exploitation of the spin selectivity of the optical transitions. In combination with millisecond-long spin coherence times originating from the high-purity crystal, we demonstrate high-fidelity optical initialization and coherent spin control, which we exploit to show coherent coupling to single nuclear spins with similar to 1 kHz resolution. The summary of our findings makes this defect a prime candidate for realising memory-assisted quantum network applications using semiconductor-based spin-to-photon interfaces and coherently coupled nuclear spins.

  • 103.
    Nagy, Roland
    et al.
    Univ Stuttgart, Germany.
    Widmann, Matthias
    Univ Stuttgart, Germany.
    Niethammer, Matthias
    Univ Stuttgart, Germany.
    Dasari, Durga B.R.
    Univ Stuttgart, Germany.
    Gerhardt, Ilja
    Univ Stuttgart, Germany; Max Planck Inst Solid State Res, Stuttgart, Germany.
    Soykal, One O.
    Naval Res Lab, Washington, DC 20375 USA.
    Radulaski, Marina
    Stanford Univ, EL Ginzton Lab, Stanford, CA 94305 USA.
    Ohshima, Takeshi
    Natl Inst Quantum & Radiol Sci & Technol, Takasaki, Gunma 3701292, Japan.
    Vuckovic, Jelena
    Stanford Univ, EL Ginzton Lab, Stanford, CA 94305 USA.
    Nguyen, Son Tien
    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.
    Economou, Sophia E.
    Virginia Polytech Inst & State Univ, Dept Phys, Blacksburg, VA 24061 USA.
    Bonato, Cristian
    Heriot Watt Univ, SUPA, Inst Photon & Quantum Sci, Edinburgh EH14 4AS, Midlothian, Scotland.
    Lee, Sang-Yun
    Korea Inst Sci & Technol, Ctr Quantum Informat, Seoul 02792, South Korea.
    Wrachtrup, Joerg
    Univ Stuttgart, Germany; Max Planck Inst Solid State Res, Stuttgart, Germany.
    Quantum Properties of Dichroic Silicon Vacancies in Silicon Carbide2018In: Physical Review Applied, E-ISSN 2331-7019, Vol. 9, no 3, article id 034022Article in journal (Refereed)
    Abstract [en]

    Although various defect centers have displayed promise as either quantum sensors, single photon emitters, or light-matter interfaces, the search for an ideal defect with multifunctional ability remains open. In this spirit, we study the dichroic silicon vacancies in silicon carbide that feature two well-distinguishable zero-phonon lines and analyze the quantum properties in their optical emission and spin control. We demonstrate that this center combines 40% optical emission into the zero-phonon lines showing the contrasting difference in optical properties with varying temperature and polarization, and a 100% increase in the fluorescence intensity upon the spin resonance, and long spin coherence time of their spin-3/2 ground states up to 0.6 ms. These results single out this defect center as a promising system for spin-based quantum technologies.

  • 104.
    Nguyen, Son Tien
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Ivanov, Ivan Gueorguiev
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Kuznetsov, A.
    Svensson, B.G.
    Zhao, Qing Xiang
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Willander, Magnus
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Morishita, N.
    Ohshima, T.
    Itoh, H.
    Isoya, J.
    Janzén, Erik
    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 .
    Recombination centers in as-grown and electron-irradiated ZnO substrates2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 102, no 9Article in journal (Refereed)
    Abstract [en]

    Optical detection of magnetic resonance (ODMR) was used to study defects in ZnO substrates irradiated with 3 MeV electrons at room temperature. The Zn vacancy and some other ODMR centers were detected. Among these, the Zn vacancy and two other centers, labeled as LU3 and LU4, were also commonly observed in different types of as-grown ZnO substrates. The LU3 and LU4 are related to intrinsic defects and act as dominating recombination centers in irradiated and as-grown ZnO. © 2007 American Institute of Physics.

  • 105.
    Nguyen, Son Tien
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Ivanov, Ivan Gueorguiev
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Kuznetsov, A.
    Svensson, B.G.
    Zhao, Q.X.
    Willander, Magnus
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Morishita, M.N.
    Ohshirma, T.
    Itoh, H.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials . Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials . Linköping University, The Institute of Technology.
    Common point defects in as-grown ZnO substrates studied by optical detection of magnetic resonance2008In: Journal of Crystal Growth, Vol. 310, 2008, Vol. 310, no 5, p. 1006-1009Conference paper (Refereed)
    Abstract [en]

    Defects in as-grown commercial zinc oxide (ZnO) substrates were studied by photoluminescence and optical detection of magnetic resonance (ODMR). In addition to the Zn vacancy and shallow donor centers, we observed several ODMR centers with spin S=1/2, labeled LU1-LU4. Among these, the axial LU3 and non-axial LU4 centers were detected in all studied samples. The ODMR signals of LU3/LU4 were found to be drastically increased after electron irradiation. The preliminary result indicates that these common ODMR centers in as-grown ZnO are related to intrinsic defects. © 2007 Elsevier B.V. All rights reserved.

  • 106.
    Nguyen, Son Tien
    et al.
    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.
    Kuznetsov, A. Yu.
    Department of Physics, Center for Materials Science and Technology, University of Oslo, Oslo, Norway.
    Svensson, B.G.
    Department of Physics, Center for Materials Science and Technology, University of Oslo, Oslo, Norway.
    Zhao, Qing Xiang
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Morishita, M.N.
    Japan Atomic Energy Agency, Takasaki, Gunma, Japan.
    Ohshima, T.
    Japan Atomic Energy Agency, Takasaki, Gunma, Japan.
    Itoh, H.
    Japan Atomic Energy Agency, Takasaki, Gunma, Japan.
    Isoya, J.
    University of Tsukuba, Tsukuba, Japan.
    Janzén, Erik
    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.
    Magnetic resonance studies of defects in electron-irradiated ZnO substrates2007In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 401-402, p. 507-510Article in journal (Refereed)
    Abstract [en]

    Optical detection of magnetic resonance (ODMR) was used to study defects in electron-irradiated ZnO substrates. In addition to the shallow donor and the Zn vacancy, several ODMR centers with an effective electron spin were detected. Among these, the axial LU3 and non-axial LU4 centers are shown to be dominating recombination centers. The annealing behavior of radiation-induced defects was studied and possible defect models are discussed.

  • 107.
    Nguyen, Son Tien
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Stenberg, Pontus
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Ascatron AB, Sweden.
    Jokubavicius, Valdas
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Abe, Hiroshi
    Natl Inst Quantum and Radiol Sci and Technol, Japan.
    Ohshima, Takeshi
    Natl Inst Quantum and Radiol Sci and Technol, Japan.
    Ul-Hassan, Jawad
    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.
    Energy levels and charge state control of the carbon antisite-vacancy defect in 4H-SiC2019In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 114, no 21, article id 212105Article in journal (Refereed)
    Abstract [en]

    The carbon antisite-vacancy pair (CSiVC) in silicon carbide (SiC) has recently emerged as a promising defect for applications in quantum communication. In the positive charge state, CSiVC+ can be engineered to produce ultrabright single photon sources in the red spectral region, while in the neutral charge state, it has been predicted to emit light at telecom wavelengths and to have spin properties suitable for a quantum bit. In this electron paramagnetic resonance study using ultrapure compensated isotope-enriched 4H-(SiC)-Si-28, we determine the (+|0) level of CSiVC and show that the positive and neutral charge states of the defect can be optically controlled.

  • 108.
    Nguyen, Son Tien
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Stenberg, Pontus
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Ascatron AB, Sweden.
    Jokubavicius, Valdas
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Ohshima, Takeshi
    Natl Inst Quantum and Radiol Sci and Technol, Japan.
    Ul-Hassan, Jawad
    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.
    Ligand hyperfine interactions at silicon vacancies in 4H-SiC2019In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 31, no 19, article id 195501Article in journal (Refereed)
    Abstract [en]

    The negative silicon vacancy (V-Si(-)) in SiC has recently emerged as a promising defect for quantum communication and room-temperature quantum sensing. However, its electronic structure is still not well characterized. While the isolated Si vacancy is expected to give rise to only two paramagnetic centers corresponding to two inequivalent lattice sites in 4H-SiC, there have been five electron paramagnetic resonance (EPR) centers assigned to V-Si(-) in the past: the so-called isolated no-zero-field splitting (ZFS) V-Si(-) center and another four axial configurations with small ZFS: T-V1a, T-V2a, T-V1b, and T-V2b. Due to overlapping with Si-29 hyperfine (hf) structures in EPR spectra of natural 4H-SiC, hf parameters of T-V1a have not been determined. Using isotopically enriched 4H-(SiC)-Si-28, we overcome the problems of signal overlapping and observe hf parameters of nearest C neighbors for all three components of the S = 3/2 T-V1a and T-V2a centers. The obtained EPR data support the conclusion that only T-V1a and T-V2a are related to V-Si(-) and the two configurations of the so-called isolated no-ZFS V-Si(-) center, V-Si(-) (I) and V-Si(-) (II), are actually the central lines corresponding to the transition I-1/2 amp;lt;-amp;gt; I + 1/2 of the T-V2a and T-V1a centers, respectively.

  • 109.
    Paskova, Tanja
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Darakchieva, Vanya
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Valcheva, E
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Ivanov, Ivan Gueorguiev
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Bottcher, T
    Roder, C
    Hommel, D
    Hydride vapor-phase epitaxial GaN thick films for quasi-substrate applications: Strain distribution and wafer bending2004In: Journal of Electronic Materials, ISSN 0361-5235, E-ISSN 1543-186X, Vol. 33, no 5, p. 389-394Article in journal (Refereed)
    Abstract [en]

    The strain distribution in thick hydride vapor-phase epitaxial (HVPE)-GaN layers grown on metal-organic vapor-phase epitaxial GaN templates was studied by means of photoluminescence, x-ray mapping, and lattice parameter analysis. A variable temperature x-ray study of the film curvature was used for verification of the strain type. The relation between the strain inhomogeneity and the wafer bending in films residing on sapphire and freestanding on the thickness of the layer and the substrate is analyzed. Possibilities to improve the uniformity of the film characteristics and to reduce the bending of the HVPE-GaN films are discussed.

  • 110.
    Pozina, Galia
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Hemmingsson, Carl
    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.
    Lundskog, Anders
    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.
    Ivanov, Ivan Gueorguiev
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Hultman, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Time-resolved photoluminescence properties of AlGaN/AlN/GaN high electron mobility transistor structures grown on 4- SiC substrate2008In: 8th International Conference on Physics of Light-Matter Coupling in Nanostructures,2008, 2008Conference paper (Other academic)
  • 111.
    Rodner, Marius
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Sensor and Actuator Systems. Linköping University, Faculty of Science & Engineering.
    Bahonjic, Jasna
    Linköping University, Department of Physics, Chemistry and Biology, Applied Sensor Science. Linköping University, Faculty of Science & Engineering.
    Mathisen, Marcus
    Not Found:Linkoping Univ, IFM, Appl Sensor Sci Unit, Linkoping, Sweden.
    Gunnarsson, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering.
    Ekeroth, Sebastian
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering.
    Helmersson, Ulf
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. 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.
    Eriksson, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Sensor and Actuator Systems. Linköping University, Faculty of Science & Engineering.
    Performance tuning of gas sensors based on epitaxial graphene on silicon carbide2018In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 153, p. 153-158Article in journal (Refereed)
    Abstract [en]

    In this study, we investigated means of performance enhancement in sensors based on epitaxial graphene on silicon carbide (SiC). Epitaxially grown graphene on SiC substrates were successfully decorated with metal oxide nanoparticles such as TiO2 and Fe3O4 using hollow cathode pulsed plasma sputtering. Atomic Force Microscopy and Raman data verified that no damage was added to the graphene surface. It could be shown that it was easily possible to detect benzene, which is one of the most dangerous volatile organic compounds, with the Fe3O4 decorated graphene sensor down to an ultra-low concentration of 5 ppb with a signal to noise ratio of 35 dB. Moreover, upon illumination with a UV light LED (265 nm) of the TiO2 decorated graphene sensor, the sensitivity towards a change of oxygen could be enhanced such that a clear sensor response could be seen which is a significant improvement over dark conditions, where almost no response occurred. As the last enhancement, the time derivative sensor signal was introduced for the sensor data evaluation, testing the response towards a change of oxygen. This sensor signal evaluation approach can be used to decrease the response time of the sensor by at least one order of magnitude. (C) 2018 Elsevier Ltd. All rights reserved.

    The full text will be freely available from 2020-05-04 09:55
  • 112.
    Santangelo, Francesca
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Sensor and Actuator Systems. Linköping University, Faculty of Science & Engineering.
    Shtepliuk, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Filippini, Daniel
    Linköping University, Department of Physics, Chemistry and Biology, Sensor and Actuator Systems. 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.
    Eriksson, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Sensor and Actuator Systems. Linköping University, Faculty of Science & Engineering.
    Real-time sensing of lead with epitaxial graphene-integrated microfluidic devices2019In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 288, p. 425-431Article in journal (Refereed)
    Abstract [en]

    Since even low concentrations of toxic heavy metals can seriously damage human health, it is important to develop simple, sensitive and accurate methods for their detection. Graphene, which is extremely sensitive to foreign species, is a key element in the development of a sensing platform where low concentrations of analyte have to be detected. This work discusses the proof of concept of a sensing platform for liquid-phase detection of heavy metals (e.g. Pb) based on epitaxial graphene sensors grown on Si-face 4H-SiC substrate (EG/SiC). The sensing platform developed includes a microfluidic chip incorporating all the features needed to connect and execute the Lab-on-chip (LOC) functions using 3D printing fast prototyping technology. Herein, we present the response of EG to concentrations of Pb2+ solutions ranging from 125 nM to 500 mu M, showing good stability and reproducibility over time and an enhancement of its conductivity with a Langmuir correlation between signal and Pb2+ concentration. Density functional theory (DFT) calculations are performed and clearly explain the conductivity changes and the sensing mechanism in agreement with the experimental results reported, confirming the strong sensitivity of the sensor to the lowest concentrations of the analyte. Furthermore, from the calibration curve of the system, a limit of detection (LoD) of 95 nM was extrapolated.

  • 113.
    Schiliro, Emanuela
    et al.
    CNR, Italy.
    Lo Nigro, Raffaella
    CNR, Italy.
    Roccaforte, Fabrizio
    CNR, Italy.
    Deretzis, Ioannis
    CNR, Italy.
    La Magna, Antonino
    CNR, Italy.
    Armano, Angelo
    Univ Palermo, Italy; Univ Catania, Italy.
    Agnello, Simonpietro
    CNR, Italy; Univ Palermo, Italy.
    Pecz, Bela
    HAS, Hungary.
    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.
    Giannazzo, Filippo
    CNR, Italy.
    Seed-Layer-Free Atomic Layer Deposition of Highly Uniform Al2O3 Thin Films onto Monolayer Epitaxial Graphene on Silicon Carbide2019In: Advanced Materials Interfaces, ISSN 2196-7350, Vol. 6, no 10, article id 1900097Article in journal (Refereed)
    Abstract [en]

    Atomic layer deposition (ALD) is the method of choice to obtain uniform insulating films on graphene for device applications. Owing to the lack of out-of-plane bonds in the sp(2) lattice of graphene, nucleation of ALD layers is typically promoted by functionalization treatments or predeposition of a seed layer, which, in turn, can adversely affect graphene electrical properties. Hence, ALD of dielectrics on graphene without prefunctionalization and seed layers would be highly desirable. In this work, uniform Al2O3 films are obtained by seed-layer-free thermal ALD at 250 degrees C on highly homogeneous monolayer (1L) epitaxial graphene (EG) (amp;gt;98% 1L coverage) grown on on-axis 4H-SiC(0001). The enhanced nucleation behavior on 1L graphene is not related to the SiC substrate, but it is peculiar of the EG/SiC interface. Ab initio calculations show an enhanced adsorption energy for water molecules on highly n-type doped 1L graphene, indicating the high doping of EG induced by the underlying buffer layer as the origin of the excellent Al2O3 nucleation. Nanoscale current mapping by conductive atomic force microscopy shows excellent insulating properties of the Al2O3 thin films on 1L EG, with a breakdown field amp;gt; 8 MV cm(-1). These results will have important impact in graphene device technology.

    The full text will be freely available from 2020-04-18 08:23
  • 114.
    Schmidt, Susann
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Czigany, Zsolt
    Hungarian Academic Science, Hungary.
    Wissting, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Greczynski, Grzegorz
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Jensen, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. 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.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    A comparative study of direct current magnetron sputtering and high power impulse magnetron sputtering processes for CNX thin film growth with different inert gases2016In: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 64, p. 13-26Article in journal (Refereed)
    Abstract [en]

    Reactive direct current magnetron sputtering (DCMS) and high power impulse magnetron sputtering (HiPIMS) discharges of carbon in different inert gas mixtures (N-2/Ne, N-2/Ar, and N-2/Kr) were investigated for the growth of carbon-nitride (CNX) thin films. Ion mass spectrometry showed that energies of abundant plasma cations are governed by the inert gas and the N-2-to-inert gas flow ratios. The population of ion species depends on the sputter mode; HiPIMS yields approximately ten times higher flux ratios of ions originating from the target to process gas ions than DCMS. Exceptional are discharges in Ne with N-2-to-Ne flow ratios <20%. Here, cation energies and the amount of target ions are highest without influence on the sputter mode. CNX thin films were deposited in 14% N-2/inert gas mixtures at substrate temperatures of 110 degrees C and 430 degrees C. The film properties show a correlation to the substrate temperature, the applied inert gas and sputter mode. The mechanical performance of the films is mainly governed by their morphology and composition, but not by their microstructure. Amorphous and fullerene-like CN0.14 films exhibiting a hardness of similar to 15 GPa and an elastic recovery of similar to 90% were deposited at 110 degrees C in reactive Kr atmosphere by DCMS and HiPIMS.

  • 115.
    Schmidt, Susann
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Goyenola, Cecilia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Gueorguiev, Gueorgui Kostov
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Jensen, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Greczynski, Grzegorz
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Gueorguiev Ivanov, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Czigany, Zs
    Hungarian Academic Science, Hungary .
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Reactive high power impulse magnetron sputtering of CFx thin films in mixed Ar/C4F4 and Ar/C4F8 discharges2013In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 542, p. 21-30Article in journal (Refereed)
    Abstract [en]

    The reactive high power impulse magnetron sputtering processes of carbon in argon/tetrafluoromethane (CF4) and argon/octafluorocyclobutane (c-C4F8) have been characterized. Amorphous carbon fluoride (CFx) films were synthesized at deposition pressure and substrate temperature of 400 mPa and 110 degrees C, respectively. The CFx film composition was controlled in the range of 0.15 andlt; x andlt; 0.35 by varying the partial pressure of the F-containing gases from 0 mPa to 110 mPa. The reactive plasma was studied employing time averaged positive ion mass spectrometry and the resulting thin films were characterized regarding their composition, chemical bonding and microstructure as well as mechanical properties by elastic recoil detection analysis, X-ray photoelectron spectroscopy, transmission electron microscopy, nanoindentation, and water droplet contact angle measurements, respectively. The experimental results were compared to results obtained by first-principles calculations based on density functional theory. The modeling of the most abundant precursor fragment from the dissociation of CF4 and C4F8 provided their relative stability, abundance, and reactivity, thus permitting to evaluate the role of each precursor during film growth. Positive ion mass spectrometry of both fluorine plasmas shows an abundance of CF+, C+, CF2+, and CF3+ (in this order) as corroborated by first-principles calculations. Only CF3+ exceeded the Ar+ signal in a CF4 plasma. Two deposition regimes are found depending on the partial pressure of the fluorine-containing reactive gas, where films with fluorine contents below 24 at.% exhibit a graphitic nature, whereas a polymeric structure applies to films with fluorine contents exceeding 27 at.%. Moreover, abundant precursors in the plasma are correlated to the mechanical response of the different CFx thin films. The decreasing hardness with increasing fluorine content can be attributed to the abundance of CF3+ precursor species, weakening the carbon matrix.

  • 116.
    Schmidt, Susann
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Goyenola, Cecilia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Gueorguiev, Gueorgui Kostov
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Jensen, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Greczynski, Grzegorz
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Czigány, Zs
    Research Institute for Technical Physics and Materials Science, Hungarian Academy of Sciences, Budapest, Hungary.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Reactive High Power Impulse Magnetron Sputtering of CFx Thin Films in Mixed Ar/CF4 and Ar/C4F8 DischargesManuscript (preprint) (Other academic)
    Abstract [en]

    The reactive high power impulse magnetron sputtering (HiPIMS) processes of C in Ar/tetrafluoromethane CF4 and Ar/octafluorocyclobutane (c-C4F8) have been characterized. Amorphous carbon fluoride (CFx) films were synthesized at deposition pressure and substrate temperature of 400 mPa and 110 oC, respectively. The CFx film composition was controlled in the range of 0.15 < x < 0.35 by varying the partial pressure of the F-containing gases from 0 mPa to 110 mPa. The reactive plasma was studied employing time averaged positive ion mass spectrometry and the resulting thin films were characterized regarding their composition, chemical bonding and microstructure as well as mechanical properties by elastic recoil detection analysis, X-ray photoelectron spectroscopy, transmission electron microscopy, nanoindentation, and water droplet contact angle measurements, respectively. The experimental results were compared to results obtained by first-principles calculations based on density functional theory.

    The modeling of the most abundant precursor fragment from the dissociation of CF4 and C4F8 provided their relative stability, abundance, and reactivity, thus permitting to evaluate the role of each precursor during film growth. Positive ion mass spectrometry of both F plasmas show an abundance of CF+, C+, CF⁺₂, and CF⁺₃ (in this order) as corroborated by first-principles calculations. Only CF⁺₃ exceeded the Ar+ signal in a CF4 plasma. Two deposition regimes are found depending on the partial pressure of the F-containing reactive gas, where films with fluorine contents below 24 at% exhibit a graphitic nature, whereas a polymeric structure applies to films with fluorine contents exceeding 27 at%. Moreover, abundant precursors in the plasma are correlated to the mechanical response of the different CFx thin films. The decreasing hardness with increasing F content can be attributed to the abundance of CF⁺₃ precursor species, weakening the C matrix.

  • 117.
    Schmidt, Susann
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Greczynski, Grzegorz
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Goyenola, Cecilia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Kostov Gueorguiev, Gueorgui
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Czigany, Zs
    Hungarian Academic Science.
    Jensen, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Gueorguiev Ivanov, Ivan
    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.
    CF(x) thin solid films deposited by high power impulse magnetron sputtering: Synthesis and characterization2011In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 206, no 4, p. 646-653Article in journal (Refereed)
    Abstract [en]

    Fluorine containing amorphous carbon films (CF(x), 0.16 andlt;= x andlt;= 0.35) have been synthesized by reactive high power impulse magnetron sputtering (HiPIMS) in an Ar/CF(4) atmosphere. The fluorine content of the films was controlled by varying the CF(4) partial pressure from 0 mPa to 110 mPa at a constant deposition pressure of 400 mPa and a substrate temperature of 110 degrees C. The films were characterized regarding their composition, chemical bonding and microstructure as well as mechanical properties by applying elastic recoil detection analysis, X-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy, and nanoindentation. First-principles calculations were carried out to predict and explain F-containing carbon thin film synthesis and properties. By geometry optimizations and cohesive energy calculations the relative stability of precursor species including C(2), F(2) and radicals, resulting from dissociation of CF4, were established. Furthermore, structural defects, arising from the incorporation of F atoms in a graphene-like network, were evaluated. All as-deposited CF(x) films are amorphous. Results from X-ray photoelectron spectroscopy and Raman spectroscopy indicate a graphitic nature of CF(x) films with x andlt;= 0.23 and a polymeric structure for films with x andgt;= 0.26. Nanoindentation reveals hardnesses between similar to 1 GPa and similar to 16 GPa and an elastic recovery of up to 98%.

  • 118.
    Shi, Yuchen
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Jokubavicius, Valdas
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Höjer, Pontus
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Yazdi, Gholamreza
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Sun, Jianwu W.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    A comparative study of high-quality C-face and Si-face 3C-SiC(1 1 1) grown on off-oriented 4H-SiC substrates2019In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 52, no 34Article in journal (Refereed)
    Abstract [en]

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

  • 119.
    Shi, Yuchen
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Zakharov, Alexei A.
    MAXIV Laboratory, Lund, Sweden.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Yazdi, Gholamreza Reza
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Jokubavicius, Valdas
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Sun, Jianwu
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Elimination of step bunching in the growth of large-area monolayer and multilayer graphene on off-axis 3CSiC (111)2018In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 140, p. 533-542Article in journal (Refereed)
    Abstract [en]

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

    The full text will be freely available from 2020-08-24 11:11
  • 120.
    Shtepliuk, Ivan I.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. NASU, Ukraine.
    Vagin, Mikhail
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Iakimov, Tihomir
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Yazdi, Gholamreza
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Lead (Pb) interfacing with epitaxial graphene2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 25, p. 17105-17116Article in journal (Refereed)
    Abstract [en]

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

  • 121.
    Shtepliuk, Ivan
    et al.
    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.
    Iakimov, Tihomir
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Kakanakova-Gueorguieva, Anelia
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Fiorenza, Patrick
    CNR IMM, Italy.
    Giannazzo, Filippo
    CNR IMM, Italy.
    Raman probing of hydrogen-intercalated graphene on Si-face 4H-SiC2019In: Materials Science in Semiconductor Processing, ISSN 1369-8001, E-ISSN 1873-4081, Vol. 96, p. 145-152Article in journal (Refereed)
    Abstract [en]

    We report the results of in-depth Raman study of quasi-free-standing monolayer graphene on the (0001) Si- face of 4H-SiC, which contains similar to 0.1-2.10(11) cm(-2) sp(3) defects that have been introduced by hydrogen intercalation. The nature of the intercalation-induced defects is elucidated and ascribed to the formation of the C-H bonds. At the higher intercalation temperature in the formed monolayer graphene the defect-related Raman scattering displays a great enhancement and new spectral features attributed to D and D+D modes appear. Comprehensive statistical analysis of the Raman data enabled us to estimate the homogeneity of the Raman scattering processes and to separate strain and doping effects. Analysis of the compressive strain and carrier density maps revealed that the intercalation temperature of 900 degrees C and intercalation time of 1 h are more favorable conditions for conversion of the buffer layer to uniformly relaxed and p-doped monolayer graphene in comparison to annealing at 1100 degrees C for 30 min.

    The full text will be freely available from 2021-03-04 17:19
  • 122.
    Shtepliuk, Ivan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. NASU, Ukraine.
    Santangelo, Maria Francesca
    Linköping University, Department of Physics, Chemistry and Biology, Sensor and Actuator Systems. Linköping University, Faculty of Science & Engineering.
    Vagin, Mikhail
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Khranovskyy, Volodymyr
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Iakimov, Tihomir
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Eriksson, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Sensor and Actuator Systems. Linköping University, Faculty of Science & Engineering.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Understanding Graphene Response to Neutral and Charged Lead Species: Theory and Experiment2018In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 11, no 10, article id 2059Article in journal (Refereed)
    Abstract [en]

    Deep understanding of binding of toxic Lead (Pb) species on the surface of two-dimensional materials is a required prerequisite for the development of next-generation sensors that can provide fast and real-time detection of critically low concentrations. Here we report atomistic insights into the Lead behavior on epitaxial graphene (Gr) on silicon carbide substrates by thorough complementary study of voltammetry, electrical characterization, Raman spectroscopy, and Density Functional Theory (DFT). It is verified that the epitaxial graphene exhibits quasi-reversible anode reactions in aqueous solutions, providing a well-defined redox peak for Pb species and good linearity over a concentration range from 1 nM to 1 mu M. The conductometric approach offers another way to investigate Lead adsorption, which is based on the formations of stable charge-transfer complexes affecting the p-type conductivity of epitaxial graphene. Our results suggest the adsorption ability of the epitaxial graphene towards divalent Lead ions is concentration-dependent and tends to saturate at higher concentrations. To elucidate the mechanisms responsible for Pb adsorption, we performed DFT calculations and estimated the solvent-mediated interaction between Lead species in different oxidative forms and graphene. Our results provide central information regarding the energetics and structure of Pb-graphene interacting complexes that underlay the adsorption mechanisms of neutral and divalent Lead species. Such a holistic understanding favors design and synthesis of new sensitive materials for water quality monitoring.

  • 123.
    Shtinkov, N.
    et al.
    Faculty of Physics, Sofia Univ., 5 James Bourchier B., Sofia, Bulgaria.
    Donchev, V.
    Faculty of Physics, Sofia Univ., 5 James Bourchier B., Sofia, Bulgaria.
    Germanova, K.
    Faculty of Physics, Sofia Univ., 5 James Bourchier B., Sofia, Bulgaria.
    Vlaev, S.
    Escuela de Física, Univ. Auton. Zacatecas, 98068 Z., ZAC, Mexico.
    Ivanov, Ivan Gueorguiev
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Effect of non-abrupt interfaces in AlAs/GaAs superlattices with embedded GaAs quantum wells2000In: Vacuum, ISSN 0042-207X, E-ISSN 1879-2715, Vol. 58, no 2, p. 561-567Article in journal (Refereed)
    Abstract [en]

    In the present paper, we investigate the effect of the non-abrupt interfaces on the electronic and optical properties of short-period AlAs/GaAs superlattices with embedded GaAs quantum wells. The lateral disorder and the component interdiffusion at the interfaces are averaged over the layer planes and are effectively represented by a diffusion concentration profile in the growth direction. The diffusion length LD is used as a parameter characterizing the degree of interface broadening. The electronic structure calculations are made using the sp3s* spin-dependent empirical tight-binding Hamiltonian, the virtual crystal approximation, and the surface Green function matching method. The dependencies of the lowest electron (E1), heavy hole (HH1), and light hole (LH1) bound states on the diffusion length are calculated for LD from 0 to 4 monolayers. It is found that the energies of the transitions (E1-HH1) and (E1-LH1) increase as LD increases. The results obtained are compared with photoluminescence data for MBE-grown samples. It is found that the degree of interface broadening depends on the growth temperature and on the sample geometry. The diffusion lengths calculated from the experimental data follow the expected trends, revealing a good qualitative agreement between theory and experiment.

  • 124.
    Son, N. T.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Isoya, J
    Graduate School of Library, Information and Media Studies, University of Tsukuba, Tsukuba, Ibaraki 305-8550, Japan.
    Ivanov, I. G.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Oshima, T
    Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan.
    Janzén, E
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Magnetic resonance identification ofhydrogen at a zinc vacancy in ZnO2013In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, p. 335804-Article in journal (Refereed)
    Abstract [en]

    Hydrogen (H) at a zinc vacancy (VZn) in ZnO is identified by electron paramagnetic resonance(EPR) and electron spin echo envelope modulation (ESEEM). In ZnO irradiated by 2 MeVelectrons, a doublet EPR spectrum, labelled S1, is observed. The doublet structure and theaccompanying weak satellites are shown to be the allowed and forbidden lines of the hyperfinestructure due to the dipolar interaction between an electron spin S D 1=2 and a nuclear spinI D 1=2 of 1H located at a VZn. The involvement of a single H atom in the S1 defect is furtherconfirmed by the observation of the nuclear Zeeman frequency of 1H in ESEEM experiments.We show that at a VZn, H prefers to make a short O–H bond with one O neighbour and is offthe substitutional site, forming a low symmetry C1 defect. In this partly H passivated VZn, the unpaired electron localizes on the p orbital of another O neighbour of VZn, and not on the H.

  • 125.
    Son, Nguyen Tien
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Isoya, J.
    University of Tsukuba, Japan .
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ohshima, T.
    Japan Atomic Energy Agency, Takasaki, Japan .
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hydrogen at zinc vacancy of ZnO: an EPR and ESEEM study2014In: International Conference on Defects in Semiconductors 2013: Proceedings of the 27th International Conference on Defectsin Semiconductors, ICDS-2013 / [ed] Anna Cavallini and Stefan K. Estreicher, American Institute of Physics (AIP), 2014, Vol. 1583, p. 341-344Conference paper (Refereed)
    Abstract [en]

    An electron paramagnetic resonance (EPR) spectrum, labeled S1, with small-splitting doublet accompanied by weak satellites is observed in ZnO irradiated with 2 MeV electrons. The obtained structure is shown to be the hyperfine structure due to the dipolar interaction between an unpaired electron spin and a nuclear spin of hydrogen (H). The observation of the nuclear Zeeman frequency of H in electron spin echo envelope modulation experiments further confirmed the presence of a hydrogen atom in S1. From the observed spin-Hamiltonian parameters, S1 is identified to be the partly H-passivated Zn vacancy,V-Zn(-) H+, with the H+ ion making a short O-H bond with only one nearest O neighbor of V-Zn in the basal plane, being off the substitutional site, while the unpaired electron spin, which gives rise to the observed EPR signal, is localized on the p orbital of another O neighbor also in the basal plane.

  • 126.
    Son, Nguyen Tien
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Isoya, J.
    University of Tsukuba.
    Umeda, T
    University of Tsukuba.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ohshima, T.
    Japan Atomic Energy Agency .
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    EPR and ENDOR Studies of Shallow Donors in SiC2010In: Applied Magnetic Resonance, ISSN 0937-9347, E-ISSN 1613-7507, Vol. 39, no 1-2, p. 49-85Article in journal (Refereed)
    Abstract [en]

    Recent progress in the investigation of the electronic structure of the shallow nitrogen (N) and phosphorus (P) donors in 3C–, 4H– and 6H–SiC is reviewed with focus on the applications of magnetic resonance including electron paramagnetic resonance (EPR) and other pulsed methods such as electron spin echo, pulsed electron nuclear double resonance (ENDOR), electron spin-echo envelope modulation and two-dimensional EPR. EPR and ENDOR studies of the 29Si and 13C hyperfine interactions of the shallow N donors and their spin localization in the lattice are discussed. The use of high-frequency EPR in combination with other pulsed magnetic resonance techniques for identification of low-temperature P-related centers in P-doped 3C–, 4H– and 6H–SiC and for determination of the valley–orbit splitting of the shallow N and P donors are presented and discussed.

  • 127.
    Stehr, Jan Eric
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Wang, Xingjun
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Filippov, Stanislav
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Pearton, S J.
    University of Florida, FL USA .
    Gueorguiev Ivanov, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Defects in N, O and N, Zn implanted ZnO bulk crystals2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 10, p. 103509-Article in journal (Refereed)
    Abstract [en]

    Comprehensive characterization of defects formed in bulk ZnO single crystals co-implanted with N and Zn as well as N and O atoms is performed by means of optically detected magnetic resonance (ODMR) complemented by Raman and photoluminescence (PL) spectroscopies. It is shown that in addition to intrinsic defects such as Zn vacancies and Zn interstitials, several N-related defects are formed in the implanted ZnO. The prevailed configuration of the defects is found to depend on the choices of the co-implants and also the chosen annealing ambient. Specifically, co-implantation with O leads to the formation of (i) defects responsible for local vibrational modes at 277, 511, and 581 cm−1; (ii) a N-related acceptor with the binding energy of 160 ± 40 meV that is involved in the donor-acceptor pair emission at 3.23 eV; and (iii) a deep donor and a deep NO acceptor revealed from ODMR. Activation of the latter defects is found to require post-implantation annealing in nitrogen ambient. None of these defects are detected when N is co-implanted with Zn. Under these conditions, the dominant N-induced defects include a deep center responsible for the 3.3128 eV PL line, as well as an acceptor center of unknown origin revealed by ODMR. Formation mechanisms of the studied defects and their role in carrier recombination are discussed.

  • 128.
    Stenberg, Pontus
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Booker, Ian Don
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Karhu, Robin
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Janzén, Erik
    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.
    Defects in silicon carbide grown by fluorinated chemical vapor deposition chemistry2018In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 535, p. 44-49Article in journal (Refereed)
    Abstract [en]

    Point defects in n- and p-type 4H-SiC grown by fluorinated chemical vapor deposition (CVD) have been characterized optically by photoluminescence (PL) and electrically by deep-level transient spectroscopy (DLTS) and minority carrier transient spectroscopy (MCTS). The results are considered in comparison with defects observed in non-fluorinated CVD growth (e.g., using SiH4 instead of SiF4 as silicon precursor), in order to investigate whether specific fluorine-related defects form during the fluorinated CVD growth, which might prohibit the use of fluorinated chemistry for device-manufacturing purposes. Several new peaks identifying new defects appear in the PL of fluorinated-grown samples, which are not commonly observed neither in other halogenated chemistries, nor in the standard CVD chemistry using silane (SiH4). However, further investigation is needed in order to determine their origin and whether they are related to incorporation of F in the SiC lattice, or not. The electric characterization does not find any new electrically-active defects that can be related to F incorporation. Thus, we find no point defects prohibiting the use of fluorinated chemistry for device-making purposes.

  • 129.
    Sun, J W
    et al.
    Groupe d’Etude des Semiconducteurs, UMR 5650, CNRS and Université Montpellier 2, Montpellier, France.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Juillaguet, S
    Groupe d’Etude des Semiconducteurs, UMR 5650, CNRS and Université Montpellier 2, Montpellier, France.
    Camassel, J
    Groupe d’Etude des Semiconducteurs, UMR 5650, CNRS and Université Montpellier 2, Montpellier, France.
    Splitting of type-I (N-B, P-Al) and type-II (N-Al, N-Ga) donor-acceptor pair spectra in 3C-SiC2011In: PHYSICAL REVIEW B, ISSN 1098-0121, Vol. 83, no 19, p. 195201-Article in journal (Refereed)
    Abstract [en]

    Discrete series of lines have been observed for many years in donor-acceptor pair (DAP) spectra in 3C-SiC. In this work, the splitting of both type-I (N-B, P-Al) and type-II (N-Al, N-Ga) DAP spectra in 3C-SiC has been systematically investigated by considering the multipole terms. For type-I spectra, in which either N or B substitutes on C sites or P and Al replace Si, the splitting energy of the substructure for a given shell is almost the same for both pairs. For type-II spectra, in which N is on the C site while Al and Ga acceptors replace Si, we find that, when compared with literature data, the splitting energy for a given shell is almost independent of the identity of the acceptor. For both type-I and type-II spectra, this splitting energy can be successfully explained by the octupole term V-3 alone with k(3)=-2x10(5) angstrom(4) meV. Comparing the experimental donor and acceptor binding energies with the values calculated by the effective-mass model, this suggests that the shallow donor (N, P) ions can be treated as point charges while the charge distribution of the acceptor ions (Al, Ga, B) is distorted in accord with the T-d point group symmetry, resulting in a considerable value for k(3). This gives a reasonable explanation for the observed splitting energies for both type-I and type-II DAP spectra.

  • 130.
    Sun, Jianwu
    et al.
    Groupe d’Etudes des Semiconducteurs, Université Montpellier 2 and CNRS, cc 074‐GES, 34095 Montpellier Cedex 5, France.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Juillaguet, S.
    Groupe d’Etudes des Semiconducteurs, Université Montpellier 2 and CNRS, cc 074‐GES, 34095 Montpellier Cedex 5, France.
    Camassel, J.
    Groupe d’Etudes des Semiconducteurs, Université Montpellier 2 and CNRS, cc 074‐GES, 34095 Montpellier Cedex 5, France.
    Splitting of type-I (N-B, P-Al) and type-II (N-Al, N-Ga) donor-acceptor pair spectra in 3C-SiC2011In: Physical Review B, ISSN 2469-9950, Vol. 83, no 19-15Article in journal (Refereed)
    Abstract [en]

    Discrete series of lines have been observed for many years in donor-acceptor pair (DAP) spectra in 3C-SiC. In this work, the splitting of both type-I (N-B, P-Al) and type-II (N-Al, N-Ga) DAP spectra in 3C-SiC has been systematically investigated by considering the multipole terms. For type-I spectra, in which either N or B substitutes on C sites or P and Al replace Si, the splitting energy of the substructure for a given shell is almost the same for both pairs. For type-II spectra, in which N is on the C site while Al and Ga acceptors replace Si, we find that, when compared with literature data, the splitting energy for a given shell is almost independent of the identity of the acceptor. For both type-I and type-II spectra, this splitting energy can be successfully explained by the octupole term V 3   alone with k 3    =   −2 × 10 5    Å 4   meV. Comparing the experimental donor and acceptor binding energies with the values calculated by the effective-mass model, this suggests that the shallow donor (N,P) ions can be treated as point charges while the charge distribution of the acceptor ions (Al,Ga,B) is distorted in accord with the T d   point group symmetry, resulting in a considerable value for k 3   . This gives a reasonable explanation for the observed splitting energies for both type-I and type-II DAP spectra.

  • 131.
    Sun, Jianwu
    et al.
    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.
    Liljedahl, Rickard
    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.
    Considerably long carrier lifetimes in high-quality 3C-SiC(111)2012In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 100, no 25, p. 252101-Article in journal (Refereed)
    Abstract [en]

    As a challenge and consequence due to its metastable nature, cubic silicon carbide (3C-SiC) has only shown inferior material quality compared with the established hexagonal polytypes. We report on growth of 3C-SiC(111) having a state of the art semiconductor quality in the SiC polytype family. The x-ray diffraction and low temperature photoluminescence measurements show that the cubic structure can indeed reach a very high crystal quality. As an ultimate device property, this material demonstrates a measured carrier lifetime of 8.2 mu s which is comparable with the best carrier lifetime in 4 H-SiC layers. In a 760-mu m thick layer, we show that the interface recombination can be neglected since almost all excess carriers recombines before reaching the interface while the surface recombination significantly reduces the carrier lifetime. In fact, a comparison of experimental lifetimes with numerical simulations indicates that the real bulk lifetime in such high quality 3C-SiC is in the range of 10-15 mu s.

  • 132.
    Svedberg, E B
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Birch, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Ivanov, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Münger, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Sundgren, Jan- Erik
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Asymmetric interface broadening in epitaxial Mo/W (001) superlattices grown by magnetron sputtering1998In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 16, no 2, p. 633-638Article in journal (Refereed)
    Abstract [en]

    The interfacial structure in epitaxial Mo/W(001) superlattices, grown by magnetron sputtering on MgO(001) substrates has been studied. The films were grown in Ar and Kr discharges at a substrate temperature of 700 degrees C, and the as-deposited samples were analyzed by x-ray diffraction and found to be epitaxial with no high-angle grain boundaries. The degree of interfacial intermixing, caused by fluxes of different energetic species impinging on the growth surface, was estimated using a combination of Monte Carlo binary collision computer codes and a gas scattering computational model. In the Ar discharge case, large asymmetries in the Mo/W and W/Mo interfaces were found, with the W/Mo interface being more than a factor of 2 broader than the Mo/W interface. Simulations of x-ray reflectivity curves using the calculated interface profiles as input parameters without any additional fitting parameters agreed very well with measured data. The overall good fit between the calculated and measured reflectivity curves using the calculated compositional profiles is an indicator that the growth simulations using TRIM based codes provides interface profiles that are reasonably accurate, which can be used as a starting point for further refinements of the details of the interface structures. (C) 1998 American Vacuum Society.

  • 133.
    Trinh, X. T.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Nilsson, D
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ivanov, I. G.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, E
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kakanakova-Georgieva, A
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Son, N.T.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Negative-U behavior of the Si donor in Al0.77Ga0.23N2013In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, no 4, p. 042101-Article in journal (Refereed)
    Abstract [en]

    Electron paramagnetic resonance (EPR) spectrum of a shallow donor is observed at low temperatures in darkness in Si-doped Al0.77Ga0.23N epitaxial layers grown on 4H-SiC substrates. It is shown from the temperature dependence of the donor concentration on the neutral donor state measured by EPR that Si is a DX (or negative-U) center but behaves as a shallow donor due to a small separation of only ∼3 meV between the neutral state Ed and the lower-lying negative state EDX. The neutral state is found to follow the effective mass theory with Ed ∼ 52–59 meV.

  • 134.
    Trinh, Xuan Thang
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Nilsson, Daniel
    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.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kakanakova-Georgieva, Anelia
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Son, Nguyen Tien
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Stable and metastable Si negative-U centers in AlGaN and AlN2014In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 16, p. 162106-1-162106-4Article in journal (Refereed)
    Abstract [en]

    Electron paramagnetic resonance studies of Si-doped AlxGa1−xN (0.79 ≤ x ≤ 1.0) reveal two Si negative-U (or DX) centers, which can be separately observed for x ≥ 0.84. We found that for the stable DX center, the energy |EDX| of the negatively charged state DX, which is also considered as the donor activation energy, abruptly increases with Al content for x ∼ 0.83–1.0 approaching ∼240 meV in AlN, whereas EDX remains to be close to the neutral charge state Ed for the metastable DX center (∼11 meV below Ed in AlN).

  • 135.
    Tzolov, M
    et al.
    Bulgarian Acad Sci, Cent Lab Solar Energy & New Energy Sources, Sofia 1784, Bulgaria Bulgarian Acad Sci, Inst Solid State Phys, Sofia 1784, Bulgaria Univ Roma La Sapienza, I-00161 Rome, Italy INFM, Unita Roma 1, I-00161 Rome, Italy Linkoping Univ, IFM, FYSIKHUSET, S-58183 Linkoping, Sweden.
    Tzenov, N
    Bulgarian Acad Sci, Cent Lab Solar Energy & New Energy Sources, Sofia 1784, Bulgaria Bulgarian Acad Sci, Inst Solid State Phys, Sofia 1784, Bulgaria Univ Roma La Sapienza, I-00161 Rome, Italy INFM, Unita Roma 1, I-00161 Rome, Italy Linkoping Univ, IFM, FYSIKHUSET, S-58183 Linkoping, Sweden.
    Dimova-Malinovska, D
    Bulgarian Acad Sci, Cent Lab Solar Energy & New Energy Sources, Sofia 1784, Bulgaria Bulgarian Acad Sci, Inst Solid State Phys, Sofia 1784, Bulgaria Univ Roma La Sapienza, I-00161 Rome, Italy INFM, Unita Roma 1, I-00161 Rome, Italy Linkoping Univ, IFM, FYSIKHUSET, S-58183 Linkoping, Sweden.
    Kalitzova, M
    Bulgarian Acad Sci, Cent Lab Solar Energy & New Energy Sources, Sofia 1784, Bulgaria Bulgarian Acad Sci, Inst Solid State Phys, Sofia 1784, Bulgaria Univ Roma La Sapienza, I-00161 Rome, Italy INFM, Unita Roma 1, I-00161 Rome, Italy Linkoping Univ, IFM, FYSIKHUSET, S-58183 Linkoping, Sweden.
    Pizzuto, C
    Bulgarian Acad Sci, Cent Lab Solar Energy & New Energy Sources, Sofia 1784, Bulgaria Bulgarian Acad Sci, Inst Solid State Phys, Sofia 1784, Bulgaria Univ Roma La Sapienza, I-00161 Rome, Italy INFM, Unita Roma 1, I-00161 Rome, Italy Linkoping Univ, IFM, FYSIKHUSET, S-58183 Linkoping, Sweden.
    Vitali, G
    Bulgarian Acad Sci, Cent Lab Solar Energy & New Energy Sources, Sofia 1784, Bulgaria Bulgarian Acad Sci, Inst Solid State Phys, Sofia 1784, Bulgaria Univ Roma La Sapienza, I-00161 Rome, Italy INFM, Unita Roma 1, I-00161 Rome, Italy Linkoping Univ, IFM, FYSIKHUSET, S-58183 Linkoping, Sweden.
    Zollo, G
    Bulgarian Acad Sci, Cent Lab Solar Energy & New Energy Sources, Sofia 1784, Bulgaria Bulgarian Acad Sci, Inst Solid State Phys, Sofia 1784, Bulgaria Univ Roma La Sapienza, I-00161 Rome, Italy INFM, Unita Roma 1, I-00161 Rome, Italy Linkoping Univ, IFM, FYSIKHUSET, S-58183 Linkoping, Sweden.
    Ivanov, Ivan Gueorguiev
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Modification of the structure of ZnO : Al films by control of the plasma parameters2001In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 396, no 1-2, p. 274-279Article in journal (Refereed)
    Abstract [en]

    ZnO:Al films were deposited by RF magnetron sputtering in triode configuration applying an external DC electric field to the substrates. Reflection high-energy electron diffraction measurements characterized the different films as consisting of randomly-oriented zinc blende crystallites or randomly and texture-oriented wurtzite crystallites, as well as of the amorphous phase. The non-resonant Raman spectra are strongly influenced by the presence of a built-in electric field at the grain boundaries and they do not depend on the symmetry of the microcrystallites. The Raman spectra taken at resonant excitation are more sensitive to the presence of the amorphous phase in the films. (C) 2001 Elsevier Science B.V. All rights reserved.

  • 136.
    Tzolov, M.
    et al.
    Ctrl. Lab. Solar Ener. New Ener. S., Bulgar. Acad. Sci., 72 T., Sofia, Bulgaria.
    Tzenov, N.
    Ctrl. Lab. Solar Ener. New Ener. S., Bulgar. Acad. Sci., 72 T., Sofia, Bulgaria.
    Dimova-Malinovska, D.
    Ctrl. Lab. Solar Ener. New Ener. S., Bulgar. Acad. Sci., 72 T., Sofia, Bulgaria.
    Kalitzova, M.
    Institute for Solid State Physics, Bulgar. Acad. Sci., 72 T., Sofia, Bulgaria.
    Pizzuto, C.
    University 'La Sapienza', INFM, Unita Roma 1, Via A. S., Rome, Italy.
    Vitali, G.
    University 'La Sapienza', INFM, Unita Roma 1, Via A. S., Rome, Italy.
    Zollo, G.
    University 'La Sapienza', INFM, Unita Roma 1, Via A. S., Rome, Italy.
    Ivanov, Ivan Gueorguiev
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Vibrational properties and structure of undoped and Al-doped ZnO films deposited by RF magnetron sputtering2000In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 379, no 1-2, p. 28-36Article in journal (Refereed)
    Abstract [en]

    Highly conductive and transparent in the visible range Al-doped ZnO (ZnO:Al) and undoped ZnO films have been deposited by RF magnetron sputtering. Reflection high-energy electron diffraction observations characterized them as textured. The habitus of the microcrystallites forming the texture depends on the Al doping. The layer texture of undoped ZnO films has texture axis parallel to the substrate. The ZnO:Al films, instead, show a columnar texture with texture axis perpendicular to the substrate. The Raman spectra of the films obtained by non-resonant excitation are completely different from those of the target material which is polycrystalline ZnO. For the interpretation of the different bands in the Raman spectra the existence of a depletion region near the grain boundaries has been assumed. The most intensive band in the Raman spectra at approximately 570 cm-1 has been assigned to electric field-induced Raman scattering on longitudinal optical phonons. The built-in electric field in the depletion region induces the Raman activity of the B2 modes and a band at 276 cm-1 appears in the spectra. Phonon modes highly localized near the grain boundaries have been detected at 516 cm-1 and 468 cm-1 which are well pronounced in the Raman spectra for the doped samples. Localized modes were observed also in the infrared reflection spectra of the doped films. Surface enhanced Raman scattering has been applied and the band in the range 830-920 cm-1 has been interpreted as due to adsorbates from the ambient air. It has been shown that the non-resonant Raman scattering can be used for qualitative study of some details of the microstructure of the zinc oxide films like the built-in electric field and the adsorbates in the films.

  • 137.
    ul-Hassan, Jawad
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Bergman, J. Peder
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    In-grown stacking faults in 4H-SiC epilayer grown on off-cut substrates2009In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 105, no 12, p. 123513-Article in journal (Other academic)
    Abstract [en]

    Different and novel in-grown stacking faults have been observed and characterized in 4H-SiC epitaxial layers grown on 4 or 8o off-cut substrates. Two different kinds of triangular stacking faults were observed in the epilayers grown on 4o off-cut substrates. The faults were formed during epitaxial growth close to the epi-substrate interface and increased continuously in size during growth. Their structural and optical properties were however different as seen from both synchrotron white beam topography and low temperature photoluminescence. The luminescence spectra were similar but appeared in different energy regions 2.85 – 2.95 eV and 2.48 – 2.64 eV, respectively which have not been observed for previously reported stacking faults. A third stacking fault was observed in 8o off-cut as-grown epilayers, sometime with higher density. A combination of back polishing, etching in molten KOH and optical microscopy revealed the geometrical structure of the stacking fault inside the epilayer. Also this fault started close to the epi-substrate interface, expanded rapidly but changed geometry after some time and reduced in size during further growth. The optical spectrum from this fault is identical to the emission from the stacking faults previously only observed and formed in the bipolar diodes during forward voltage operation.

  • 138.
    ul-Hassan, Jawad
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Virojanadara, Chariya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Meyer, A.
    Institute of Solid State Physics, University of Bremen, Germany.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Flege, J. I.
    Institute of Solid State Physics, University of Bremen, Germany.
    Watcharinyanon, Somsakul
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Falta, J
    Institute of Solid State Physics, University of Bremen, 28359 Bremen, Germany.
    Johansson, Leif I.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Control of epitaxial graphene thickness on 4H-SiC(0001) and bufferlayer removal through hydrogen intercalation2012In: Materials Science Forum (Volumes 717 - 720), Trans Tech Publications Inc., 2012, Vol. 717-720, p. 605-608Conference paper (Refereed)
    Abstract [en]

    We report graphene thickness, uniformity and surface morphology dependence on thegrowth temperature and local variations in the off-cut of Si-face 4H-SiC on-axis substrates. Thetransformation of the buffer layer through hydrogen intercalation and the subsequent influence onthe charge carrier mobility are also studied. A hot-wall CVD reactor was used for in-situ etching,graphene growth in vacuum and the hydrogen intercalation process. The number of graphene layersis found to be dependent on the growth temperature while the surface morphology also depends onthe local off-cut of the substrate and results in a non-homogeneous surface. Additionally, the influence of dislocations on surface morphology and graphene thickness uniformity is also presented.

  • 139.
    ul-Hassan, Jawad
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Winters, M.
    Chalmers, Sweden.
    Gueorguiev Ivanov, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Habibpour, O.
    Chalmers, Sweden.
    Zirath, H.
    Chalmers, Sweden.
    Rorsman, N.
    Chalmers, Sweden.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Quasi-free-standing monolayer and bilayer graphene growth on homoepitaxial on-axis 4H-SiC(0001) layers2015In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 82, p. 12-23Article in journal (Refereed)
    Abstract [en]

    Quasi-free-standing monolayer and bilayer graphene is grown on homoepitaxial layers of 4H-SiC. The SiC epilayers themselves are grown on the Si-face of nominally on-axis semi-insulating substrates using a conventional SiC hot-wall chemical vapor deposition reactor. The epilayers were confirmed to consist entirely of the 4H polytype by low temperature photoluminescence. The doping of the SiC epilayers may be modified allowing for graphene to be grown on a conducing substrate. Graphene growth was performed via thermal decomposition of the surface of the SiC epilayers under Si background pressure in order to achieve control on thickness uniformity over large area. Monolayer and bilayer samples were prepared through the conversion of a carbon buffer layer and monolayer graphene respectively using hydrogen intercalation process. Micro-Raman and reflectance mappings confirmed predominantly quasi-free-standing monolayer and bilayer graphene on samples grown under optimized growth conditions. Measurements of the Hall properties of Van der Pauw structures fabricated on these layers show high charge carrier mobility (greater than 2000 cm(2)/Vs) and low carrier density (less than0.9 x 10(13) cm(-2)) in quasi-free-standing bilayer samples relative to monolayer samples. Also, bilayers on homoepitaxial layers are found to be superior in quality compared to bilayers grown directly on SI substrates.

  • 140.
    Vagin, Mikhail
    et al.
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology.
    Sekretareva, Alina
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. Stanford Univ, CA 94305 USA; Uppsala Univ, Sweden.
    Håkansson, Anna
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology.
    Iakimov, Tihomir
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Graphens AB, Teknikringen 1F, SE-58330 Linkoping, Sweden.
    Ivanov, Ivan Gueorguiev
    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. Graphens AB, Teknikringen 1F, SE-58330 Linkoping, Sweden.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Graphens AB, Teknikringen 1F, SE-58330 Linkoping, Sweden.
    Lundström, Ingemar
    Linköping University, Department of Physics, Chemistry and Biology, Sensor and Actuator Systems. Linköping University, Faculty of Science & Engineering.
    Eriksson, Mats
    Linköping University, Department of Physics, Chemistry and Biology, Sensor and Actuator Systems. Linköping University, Faculty of Science & Engineering.
    Bioelectrocatalysis on Anodized Epitaxial Graphene and Conventional Graphitic Interfaces2019In: CHEMELECTROCHEM, ISSN 2196-0216, Vol. 6, no 14, p. 3791-3796Article in journal (Refereed)
    Abstract [en]

    Graphitic materials exhibit significant anisotropy due to the difference in conductivity in a single layer and between adjacent layers. This anisotropy is manifested on epitaxial graphene (EG), which can be manipulated on the nanoscale in order to provide tailor-made properties. Insertion of defects into the EG lattice was utilized here for controllable surface modification with a model biocatalyst and the properties were quantified by both electrochemical and optical methods. A comparative evaluation of the electrode reaction kinetics on the enzyme-modified 2D material vs conventional carbon electrode materials revealed a significant enhancement of mediated bioelectrocatalysis at the nanoscale.

  • 141.
    Vagin, Mikhail
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Sekretareva, Alina
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. Department of Chemistry, Stanford University, Stanford, USA.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Håkansson, Anna
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Iakimov, Tihomir
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Graphensic AB, Teknikringen 1F, Linköping, Sweden.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Graphensic AB, Teknikringen 1F, Linköping, Sweden.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Graphensic AB, Teknikringen 1F, Linköping, Sweden.
    Lundström, Ingemar
    Linköping University, Department of Physics, Chemistry and Biology, Biosensors and Bioelectronics. Linköping University, Faculty of Science & Engineering.
    Eriksson, Mats
    Linköping University, Department of Physics, Chemistry and Biology, Chemical and Optical Sensor Systems. Linköping University, Faculty of Science & Engineering.
    Monitoring of epitaxial graphene anodization2017In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 238, p. 91-98Article in journal (Refereed)
    Abstract [en]

    Anodization of a graphene monolayer on silicon carbide was monitored with electrochemical impedance spectroscopy. Structural and functional changes of the material were observed by Raman spectroscopy and voltammetry. A 21 fold increase of the specific capacitance of graphene was observed during the anodization. An electrochemical kinetic study of the Fe(CN)(6)(3) (/4) redox couple showed a slow irreversible redox process at the pristine graphene, but after anodization the reaction rate increased by several orders of magnitude. On the other hand, the Ru(NH3) (3+/2+)(6) redox couple proved to be insensitive to the activation process. The results of the electron transfer kinetics correlate well with capacitance measurements. The Raman mapping results suggest that the increased specific capacitance of the anodized sample is likely due to a substantial increase of electron doping, induced by defect formation, in the monolayer upon anodization. The doping concentration increased from less than 1 x 10(13) of the pristine graphene to 4-8 x 10(13) of the anodized graphene. (C) 2017 Elsevier Ltd. All rights reserved.

  • 142.
    Wagner, Matthias
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Ivanov, Ivan Gueorguiev
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Storasta, Liutauras
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Bergman, JP
    Magnusson, Björn
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Photoluminescence up-conversion processes in SiC2003In: Materials Science Forum, Vols. 433-436, 2003, Vol. 433-4, p. 309-312Conference paper (Refereed)
    Abstract [en]

    Efficient photoluminescence up-conversion is observed in 4H SiC samples containing both the UD-3 defect with its characteristic photoluminescence (PL) no-phonon (NP) line in the near infrared at 1.356 eV and the titanium impurity with its emission in the visible spectral region. When both defects are present, the titanium emission can be excited efficiently by tuning the laser to UD-3. In 4H samples containing either only UD-3 or only titanium, a different photoluminescence up-conversion process can be observed. This second process occurs at photon energies higher than approximately 1.5 eV without exhibiting a clear threshold. In 6H and 15R SiC only this second process was found, even when both the UD-3 defect and the titanium impurity are abundant.

  • 143.
    Wagner, Matthias
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Ivanov, Ivan Gueorguiev
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Storasta, Liutauras
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Magnusson, Björn
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Photoluminescence upconversion in 4H-SiC2002In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 81, no 14, p. 2547-Article in journal (Refereed)
    Abstract [en]

     Efficient photoluminescence upconversion is observed in 4H-SiC samples containing both the UD-3 defect and the titanium impurity. In this process, the titanium photoluminescence emission with no-phonon (NP) lines at 2.848 eV (A0) and 2.789 eV (B0) can be excited by tuning the laser to the NP line of UD-3 at 1.356 eV. In samples containing either only UD-3 or only titanium, a different photoluminescence upconversion process can be observed, which occurs at photon energies higher than ~1.5 eV without exhibiting sharp features. At least one of the two processes generates both free electrons and free holes and can, therefore, be a candidate for an important recombination channel.

  • 144.
    Wang, Xiangjun
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics .
    Olafsson, S
    Madsen, LD
    Linkoping Univ, Dept Phys, SE-58183 Linkoping, Sweden Swedish Def Res Agcy, FOI, SE-58111 Linkoping, Sweden Royal Inst Technol, Dept Condensed Matter Phys, SE-16440 Stockholm, Sweden.
    Rudner, S
    Ivanov, Ivan Gueorguiev
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Grishin, A
    Linkoping Univ, Dept Phys, SE-58183 Linkoping, Sweden Swedish Def Res Agcy, FOI, SE-58111 Linkoping, Sweden Royal Inst Technol, Dept Condensed Matter Phys, SE-16440 Stockholm, Sweden.
    Helmersson, Ulf
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics .
    Growth and characterization of Na0.5K0.5NbO3 thin films on polycrystalline Pt80Ir20 substrates2002In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 17, no 5, p. 1183-1191Article in journal (Refereed)
    Abstract [en]

    Na0.5K0.5NbO3 thin films have been deposited onto textured polycrystalline Pt80Ir20 substrates using radio frequency magnetron sputtering. Films were grown in off- and on-axis positions relative to the target at growth temperatures of 500-700 degreesC and sputtering pressures of 1-7 Pa. The deposited films were found to be textured, displaying a mixture of two orientations (001) and (101). Films grown on-axis showed a prefered (001) orientation, while the off-axis films had a (101) orientation. Scanning electron microscopy showed that the morphology of the films was dependent on the substrate position and sputtering pressure. The low-frequency (10 kHz) dielectric constants of the films were found to be in the range of approximately 490-590. Hydrostatic piezoelectric measurements showed that the films were piezoelectric in the as-deposited form with a constant up to 14.5 pC/N.

  • 145.
    Wang, Xin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Helmersson, Ulf
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.
    Madsen, Lynnette D
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Ivanov, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Münger, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Rudner, Staffan
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Hjörvarsson, B
    Department of Physics, Uppsala University, Sweden.
    Sundgren, Jan-Erik
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Composition, structure, and dielectric tunability of epitaxial SrTiO3 thin films grown by radio frequency magnetron sputtering1999In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 17, no 2, p. 564-570Article in journal (Refereed)
    Abstract [en]

    Epitaxial (001) oriented SrTiO3 films have been deposited on LaAlO3(001) substrates by off-axis radio frequency magnetron sputtering in Ar:O-2 gas mixtures at substrate temperatures ranging from 650 to 850 degrees C. For the deposition conditions used, stoichiometric targets yielded 20% Sr-deficient films, whereas Sr-enriched targets (Sr1.1TiO0.9O3.0) resulted in stoichiometric films. The Sr-deficient films had a mosaic structure and a larger lattice parameter in comparison to bulk SrTiO3. The stoichiometric films on the other hand had a much higher crystalline quality in the as-deposited condition. The mosaicity of the latter films was primarily limited by the crystalline quality of the LaAlO3 substrates. The lattice parameters of the stoichiometric films were also smaller than the Sr-deficient ones and closer to the bulk value. The dielectric properties of the stoichiometric films were superior to the Sr-deficient films. For films with a thickness of similar to 300 nm, the typical dielectric constants as measured at similar to 77 K and I MHz were determined to be 820 and 500, for the stoichiometric and Sr-deficient films, respectively. Also the capacitance change, as a direct current bias voltage was applied to an interdigital capacitor, was higher for the stoichiometric film, 27.3% as compared to 8.6% when applying a bias of 300 V at 77 K. We also demonstrate the effectiveness of thermal annealing in improving both crystalline quality and dielectric properties, especially for the Sr-deficient films. (C) 1999 American Vacuum Society. [S0734-2101(99)010002-7].

  • 146.
    Westlund, A.
    et al.
    Chalmers, Dept Microtechnol & Nanosci MC2, SE-41296 Gothenburg, Sweden.
    Winters, M.
    Chalmers, Dept Microtechnol & Nanosci MC2, SE-41296 Gothenburg, Sweden.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Ul-Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Nilsson, P. -A.
    Chalmers, Dept Microtechnol & Nanosci MC2, SE-41296 Gothenburg, Sweden.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Rorsman, N.
    Chalmers, Dept Microtechnol & Nanosci MC2, SE-41296 Gothenburg, Sweden.
    Grahn, J.
    Chalmers, Dept Microtechnol & Nanosci MC2, SE-41296 Gothenburg, Sweden.
    Correction: Graphene self-switching diodes as zero-bias microwave detectors (vol 106, 093116, 2015)2015In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 106, no 15, article id 159902Article in journal (Other academic)
    Abstract [en]

    n/a

  • 147.
    Westlund, A.
    et al.
    Chalmers, Sweden.
    Winters, M.
    Chalmers, Sweden.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ul-Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Nilsson, P. -A.
    Chalmers, Sweden.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Rorsman, N.
    Chalmers, Sweden.
    Grahn, J.
    Chalmers, Sweden.
    Graphene self-switching diodes as zero-bias microwave detectors2015In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 106, no 9, p. 093116-Article in journal (Refereed)
    Abstract [en]

    Self-switching diodes (SSDs) were fabricated on as-grown and hydrogen-intercalated epitaxial graphene on SiC. The SSDs were characterized as zero-bias detectors with on-wafer measurements from 1 to 67 GHz. The lowest noise-equivalent power (NEP) was observed in SSDs on the hydrogen-intercalated sample, where a flat NEP of 2.2 nW/Hz(1/2) and responsivity of 3.9 V/W were measured across the band. The measured NEP demonstrates the potential of graphene SSDs as zero-bias microwave detectors. (C) 2015 AIP Publishing LLC.

  • 148.
    Winters, M.
    et al.
    Chalmers, Sweden.
    Habibpour, O.
    Chalmers, Sweden.
    Gueorguiev Ivanov, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    ul-Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Zirath, H.
    Chalmers, Sweden.
    Rorsman, N.
    Chalmers, Sweden.
    Assessment of H-intercalated graphene for microwave FETs through material characterization and electron transport studies2015In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 81, p. 96-104Article in journal (Refereed)
    Abstract [en]

    Epitaxial graphene is grown on semi-insulating (SI) 4H-SiC in a hot wall CVD reactor by graphitization and in-situ intercalation with (H)ydrogen. A holistic material characterization is performed in order to ascertain the number of layers, layer uniformity, and electron transport properties of the epi-layers via electronic test structures and Raman spectroscopy. Bilayer graphene field effect transistors (GFETs) are fabricated using a full electron beam lithography (EBL) process which is optimized for low contact resistances of r(c) less than 0.2 Omega mm. Mobilities of order 2500 cm(2)/V s are achieved on bilayer samples after fabrication. The devices demonstrate high transconductance g(m) = 400 mS/mm and high current density I-ds = 1.8 A/mm. The output conductance at the bias of maximum transconductance is g(ds) = 300 mS/mm. The GFETs demonstrate an extrinsic f(t)(ext) and f(max)(ext) of 20 and 13 GHz, respectively and show 6 dB power gain at 1 GHz in a 50 Omega system, which is the highest reported to date.

  • 149.
    Yakimova, Rositsa
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Gueorguiev Ivanov, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Vines, Lasse
    University of Oslo, Norway.
    Linnarsson, Margareta K.
    KTH Royal Institute Technology, Sweden.
    Gällström, Andreas
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Giannazzo, Filippo
    CNR, Italy.
    Roccaforte, Fabrizio
    CNR, Italy.
    Wellmann, Peter
    University of Erlangen Nurnberg, Germany.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Jokubavicius, Valdas
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Growth, Defects and Doping of 3C-SiC on Hexagonal Polytypes2017In: ECS Journal of Solid State Science and Technology, ISSN 2162-8769, E-ISSN 2162-8777, Vol. 6, no 10, p. P741-P745Article in journal (Refereed)
    Abstract [en]

    Technologies for the growth of 3C-SiC with crystalline quality and crystal size similar to hexagonal counterparts (6H- or 4H-SiC) are still at the laboratory stage. There are several challenges in the control of polytype stability and formation of structural defects which have to be eliminated to reveal the full potential of this material. Nevertheless, 3C-SiC has been explored for various energy, environment and biomedical applications which significantly benefit from the intrinsic semiconductor properties of this material. The future of 3C-SiC and its applications depends on the advances which will be made in improving crystalline quality, enlarging crystal size and controlling doping levels which have not been entirely explored due to the lack of high quality 3C-SiC substrates. This paper reviews recent progress in growth and doping of thick 3C-SiC layers on hexagonal SiC substrates using sublimation epitaxy. It covers the growth process on off-axis substrates and defects occurrence, as well as the issue of obtaining high resistivity material. (c) 2017 The Electrochemical Society. All rights reserved.

  • 150.
    Yakimova, Rositsa
    et al.
    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.
    Vines, L.
    Univ Oslo, Norway.
    Linnarsson, M. K.
    KTH Royal Inst Technol, Sweden.
    Gällström, Andreas
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Giannazzo, F.
    CNR IMM, Italy.
    Roccaforte, F.
    CNR IMM, Italy.
    Wellmann, P.
    Univ Erlangen Nurnberg, Germany.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Jokubavicius, Valdas
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Growth, Defects and Doping of 3C-SiC on Hexagonal Polytypes2017In: GALLIUM NITRIDE AND SILICON CARBIDE POWER TECHNOLOGIES 7, ELECTROCHEMICAL SOC INC , 2017, Vol. 80, no 7, p. 107-115Conference paper (Refereed)
    Abstract [en]

    Technologies for the growth of 3C-SiC with crystalline quality and crystal size similar to hexagonal counterparts (6H-or 4H-SiC) are still at the laboratory stage. There are several challenges in the control of polytype stability and formation of structural defects which have to be eliminated to reveal the full potential of this material. Nevertheless, 3C-SiC has been explored for various energy, environment and biomedical applications which significantly benefit from the intrinsic semiconductor properties of this material. The future of 3C-SiC and its applications depends on the advances which will be made in improving crystalline quality, enlarging crystal size and controlling doping levels which have not been entirely explored due to the lack of high quality 3C-SiC substrates. This paper reviews recent progress in growth and doping of thick 3C-SiC layers on hexagonal SiC substrates using sublimation epitaxy. It covers the growth process on off-axis substrates and defects occurrence, as well as the issue of obtaining high resistivity material.

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