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  • 51.
    Jain, Vishal
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab). Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Nowzari, Ali
    Lund University, Lund, Sweden.
    Wallentin, Jesper
    Lund University, Lund, Sweden.
    Borgström, Magnus T.
    Lund University, Lund, Sweden.
    Messing, Maria E.
    Lund University, Lund, Sweden.
    Asoli, Damir
    Ideon Science Park, Sol Voltaics AB, Lund, Sweden.
    Graczyk, Mariusz
    Lund University, Lund, Sweden.
    Witzigmann, Bernd
    University of Kassel, Kassel, Germany .
    Capasso, Federico
    Harvard University, Cambridge, Massachusetts, USA.
    Samuelson, Lars
    Lund University, Lund, Sweden.
    Pettersson, Håkan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Study of photocurrent generation in InP nanowire-based p+–i–n+ photodetectors2014Inngår i: Nano Reseach, ISSN 1998-0124, E-ISSN 1998-0000, Vol. 7, nr 4, s. 544-552Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on electrical and optical properties of p+-i-n+ photodetectors/solar cells based on square millimeter arrays of InP nanowires grown on InP substrates. The study includes a sample series where the p+-segment length was varied between 0 and 250nm, as well as solar cells with 9.3% efficiency with similar design. The electrical data for all devices display clear rectifying behavior with an ideality factor between 1.8 and 2.5 at 300K. From spectrally resolved photocurrent measurements, we conclude that the photocurrent generation process depends strongly on the p+-segment length. Without p+-segment, photogenerated carriers funneled from the substrate into the NWs contribute strongly to the photocurrent. Adding a p+-segment decouples the substrate and shifts the depletion region, and collection of photogenerated carriers, to the nanowires, in agreement with theoretical modeling. In optimized solar cells, clear spectral signatures of interband transitions in the ZB and WZ InP layers of the mixed-phase i-segments are observed. Complementary electroluminescence, TEM as well as measurements of the dependence of the photocurrent on angle of incidence and polarization, support our interpretations. © 2014 Tsinghua University Press and Springer-Verlag Berlin Heidelberg.

  • 52.
    Jain, Vishal
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Wallentin, Jesper
    Physics Department, Lund University, Lund, Sweden.
    Borgström, Magnus
    Physics department, Lund university, Lund, Sweden.
    Storm, Kristian
    Physics Department, Lund University, Lund, Sweden.
    Landin, Lars
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Wickert, Peter
    Sol Voltaics AB, Lund, Sweden.
    Capasso, Federico
    Harvard University, Cambridge, Massachusetts, USA.
    Samuelson, Lars
    Physics Department, Lund university, Lund, Sweden.
    Pettersson, Håkan
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    A comparative study of nanowire based infrared p+-i-n+ photodetectors2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We present a comparative study of electrical and optical properties of two types of p+-i-n+ photodetectors based on self-assembled ensembles of vertical InP nanowires (NWs) monolithically grown on InP. The detectors differ in the type of p+ contact, one detector geometry has p+-i-n+ segments integrated into the NWs (type A) while the other detector has i-n+ NW segments grown directly on a p+ substrate(type B). The samples were prepared by first depositing 80 nm Au nanoparticles on a p+ InP substrate using an aerosol technique and subsequently growing NWs using MOVPE. The NWs have a polytypecrystal structure of alternating wurtzite and zincblende segments. The processing of the detectors include deposition of SiO2, followed by an etching step to remove the oxide from the tip of the NWs, and finally sputtering of ITO on 1x1 mm2 device areas. The two most prominent differences between the detectors concern the current-voltage (I-V) characteristics and the spatial location of generated photocurrent. From spectrally resolved photocurrent measurements, we conclude that the photocurrent in detector type A is primarily generated in the NWs, whereas the photocurrent in type B detectors mainly stems from the substrate. Photogenerated carriers in the substrate diffuse to the NWs where they are effectively funnelled into the NWs. The I-V characteristics of the type A detector displays a non-trivial transport behaviour for forward biases, whereas type B shows excellent rectifying behavior with an ideality factor of about 2.5. We will discuss detailed analysis of the spectral fingerprints of the two detector types revealing the mixed crystal phase of the polytype NWs and bandstructure effects, temperature dependence of the I-V characteristics and typical photodetector parameters.

  • 53.
    Jain, Vishal
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab). Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Wallentin, Jesper
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Nowzari, Ali
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Heurlin, Magnus
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Asoli, Damir
    Sol Voltaics AB, Lund, Sweden.
    Borgström, Magnus T.
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Capasso, Federico
    School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA.
    Samuelson, Lars
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Pettersson, Håkan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab). Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Processing and Characterization of Nanowire Arrays for Photodetectors2015Inngår i: Nano-Structures for Optics and Photonics: Optical Strategies for Enhancing Sensing, Imaging, Communication and Energy Conversion / [ed] Baldassare Di Bartolo, John Collins & Luciano Silvestri, Dordrecht: Springer, 2015, s. 511-512Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We present a fabrication scheme of contacting arrays of vertically standing nanowires (NW) for LEDs (Duan et al. Nature 409:66–69, 2001), photodetectors (Wang et al. Science (NY) 293:1455–1457, 2001) or solar cell applications (Wallentin et al. Science (NY) 339:1057–1060, 2013). Samples were prepared by depositing Au films using nano-imprint lithography (Må rtensson et al. Nano Lett 4:699–702, 2004) which are used as catalysts for NW growth in a low-pressure metal organic vapour phase epitaxy system where III-V precursors and dopant gases are flown at elevated temperatures which lead to the formation of NWs with different segments (Borgström et al. Nano Res 3:264–270, 2010). An insulating SiO2 layer is then deposited and etched from the top segments of the NWs followed by sputtering of a transparent top conducting oxide and opening up 1 × 1 mm2 device areas through a UV lithography step and etching of the top contact from non-device areas. A second UV lithography step was subsequently carried out to open up smaller windows on the ITO squares for bond pad definition, followed by metallization and lift-off; and the substrate is used as back contact. We also report on the electrical and optical properties of near-infrared p+−i−n+ photodetectors/solar cells based on square millimeter ensembles of InP nanowires grown on InP substrates. The study includes a sample series where the p +-segment length was varied between 0 and 250 nm, as well as solar cell samples with 9.3 % efficiency with similar design. The NWs have a complex modulated crystal structure of alternating wurtzite and zincblende segments, a polytypism that depends on dopant type. The electrical data for all samples display excellent rectifying behavior with an ideality factor of about 2 at 300 K. From spectrally resolved photocurrent measurements, we conclude that the photocurrent generation process depends strongly on the p +-segment length. Without p +-segment in the NWs, photogenerated carriers funneled from the substrate into the NWs contribute significantly to the photocurrent. Adding a p +-segment shifts the depletion region up into the i-region of the NWs reducing the substrate contribution to photocurrent while strongly improving the collections of carriers generated in the NWs, in agreement with theoretical modeling (Fig. 48.1). © Springer Science+Business Media Dordrecht 2015.

  • 54.
    Johannes, Andreas
    et al.
    Institute for Solid State Physics, Friedrich-Schiller-University Jena, Jena, Germany.
    Noack, Stefan
    Institute for Solid State Physics, Friedrich-Schiller-University Jena, Jena, Germany.
    Paschoal Jr, Waldomiro
    Högskolan i Halmstad, Akademin för informationsteknologi. Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Kumar, Sandeep
    Högskolan i Halmstad, Akademin för informationsteknologi. Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Jacobsson, Daniel
    Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Pettersson, Håkan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab). Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Samuelson, Lars
    Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Dick, Kimberly A.
    Centre for Analysis and Synthesis, Lund University, Lund, Sweden.
    Martinez-Criado, G.
    European Synchrotron Radiation Facility, Grenoble, France.
    Burghammer, M.
    European Synchrotron Radiation Facility, Grenoble, France.
    Ronning, Carsten
    Institute for Solid State Physics, Friedrich-Schiller-University Jena, Jena, Germany.
    Enhanced sputtering and incorporation of Mn in implanted GaAs and ZnO nanowires2014Inngår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 47, nr 39, artikkel-id 394003Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We simulated and experimentally investigated the sputter yield of ZnO and GaAs nanowires, which were implanted with energetic Mn ions at room temperature. The resulting thinning of the nanowires and the dopant concentration with increasing Mn ion fluency were measured by accurate scanning electron microscopy (SEM) and nano-x-Ray Fluorescence (nanoXRF) quantification, respectively. We observed a clearly enhanced sputter yield for the irradiated nanowires compared to bulk, which is also corroborated by iradina simulations. These show a maximum if the ion range matches the nanowire diameter. As a consequence of the erosion thinning of the nanowire, the incorporation of the Mn dopants is also enhanced and increases non-linearly with increasing ion fluency. © 2014 IOP Publishing Ltd.

  • 55.
    Johansson, Jan Olof
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Hössjer, Ola G.
    Department of Mathematics, Stockholm University, Sweden.
    A shot-noise model for paper fibres with non-uniform random orientations2005Inngår i: Scandinavian Journal of Statistics, ISSN 0303-6898, E-ISSN 1467-9469, Vol. 32, nr 3, s. 351-363Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The surface properties of newsprint and other paper qualities are to a great extent determined by the properties of the cellulose fibres. An appropriate description of these fibres as they appear in the paper is therefore important and can be used for quality classification and process monitoring. We suggest a model that considers the fibre geometry and appearance. It is based on a two-dimensional shot-noise process. The model is fit by minimizing a weighted least squares distance between the model-based and estimated covariance functions and this provides estimates of the fibre size, intensity and the non-uniform distribution of the fibre orientation. The model is applied to simulated and real data.

  • 56.
    Juszczuk, Agnieszka Beata
    et al.
    Högskolan i Halmstad. Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE). Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Tkacheva, Evgeniya
    Högskolan i Halmstad. Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE). Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Revision Moment for the Retail Decision-Making System2010Independent thesis Advanced level (degree of Master (One Year)), 10 poäng / 15 hpOppgave
    Abstract [en]

    In this work we address to the problems of the loan origination decision-making systems. In accordance with the basic principles of the loan origination process we considered the main rules of a clients parameters estimation, a change-point problem for the given data and a disorder moment detection problem for the real-time observations. In the first part of the work the main principles of the parameters estimation are given. Also the change-point problem is considered for the given sample in the discrete and continuous time with using the Maximum likelihood method. In the second part of the work the disorder moment detection problem for the real-time observations is considered as a disorder problem for a non-homogeneous Poisson process. The corresponding optimal stopping problem is reduced to the free-boundary problem with a complete analytical solution for the case when the intensity of defaults increases. Thereafter a scheme of the real time detection of a disorder moment is given.

  • 57.
    Karimi, Mohammad
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab). Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Heurlin, Magnus
    Solid State Physics and NanoLund, Lund University, Lund, Sweden & Sol Voltaics AB, Lund, Sweden.
    Limpert, Steven
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Jain, Vishal
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS). Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Mansouri, Ebrahim
    Högskolan i Halmstad, Akademin för informationsteknologi.
    Zeng, Xulu
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Samuelson, Lars
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Linke, Heiner
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Borgström, Magnus T.
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Pettersson, Håkan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Nanowire photodetectors with embedded quantum heterostructures for infrared detection2019Inngår i: Infrared physics & technology, ISSN 1350-4495, E-ISSN 1879-0275, Vol. 96, s. 209-212Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nanowires offer remarkable opportunities for realizing new optoelectronic devices because of their unique fundamental properties. The ability to engineer nanowire heterostructures with large bandgap variations is particularly interesting for technologically important broadband photodetector applications. Here we report on infrared photodetectors based on arrays of InP nanowires with embedded InAsP quantum discs. We demonstrate a strongly reduced dark current in the detector elements by compensating the unintentional n-doping in the nominal intrinsic region of the InP nanowires by in-situ doping with Zn, a crucial step towards realizing high-performance devices. The optimized array detectors show a broad spectral sensitivity at normal incidence for wavelengths from visible to far-infrared up to 20 μm, promoted by both interband and intersubband transitions. Optical simulations show that the unexpected normal incidence response at long wavelengths is due to non-zero longitudinal modes hosted by the nanowires. © 2018 Elsevier B.V.

  • 58.
    Karimi, Mohammad
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab). Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Heurlin, Magnus
    Solid State Physics and NanoLund, Lund University, Lund, Sweden & Sol Voltaics AB, Lund, Sweden.
    Limpert, Steven
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Jain, Vishal
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab). Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Zeng, Xulu
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Geijselaers, Irene
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Nowzari, Ali
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Fu, Ying
    Department of Applied Physics, Royal Institute of Technology (KTH), Solna, Sweden.
    Samuelson, Lars
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Linke, Heiner
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Borgström, Magnus T.
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Pettersson, Håkan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab). Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Intersubband Quantum Disc-in-Nanowire Photodetectors with Normal-Incidence Response in the Long-Wavelength Infrared2018Inngår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 18, nr 1, s. 365-372Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Semiconductor nanowires have great potential for realizing broadband photodetectors monolithically integrated with silicon. However, the spectral range of such detectors has so far been limited to selected regions in the ultraviolet, visible and near-infrared. Here, we report on the first intersubband nanowire heterostructure array photodetectors exhibiting a spectrally resolved photoresponse from the visible to long-wavelength infrared. In particular, the infrared response from 3-20 mm is enabled by intersubband transitions in low-bandgap InAsP quantum discs synthesized axially within InP nanowires. The intriguing optical characteristics, including unexpected sensitivity to normal incident radiation, are explained by excitation of the longitudinal component of optical modes in the photonic crystal formed by the nanostructured portion of the detectors. Our results provide a generalizable insight into how broadband nanowire photodetectors may be designed, and how engineered nanowire heterostructures open up new fascinating opportunities for optoelectronics.

  • 59.
    Karimi, Mohammad
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab). Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Jain, Vishal
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab). Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Heurlin, Magnus
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Nowzari, Ali
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Hussain, Laiq
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS). Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Lindgren, David
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Stehr, Jan Eric
    Department of Physics, Chemistry and Biology, Linköping University, Linköping, Sweden.
    Buyanova, Irina A.
    Department of Physics, Chemistry and Biology, Linköping University, Linköping, Sweden.
    Gustafsson, Anders
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Samuelson, Lars
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Borgström, Magnus T.
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Pettersson, Håkan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS). Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Room-temperature InP/InAsP Quantum Discs-in-Nanowire Infrared Photodetectors2017Inngår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 17, nr 6, s. 3356-3362Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The possibility to engineer nanowire heterostructures with large bandgap variations is particularly interesting for technologically important broadband photodetector applications. Here we report on a combined study of design, fabrication, and optoelectronic properties of infrared photodetectors comprising four million n+–i–n+ InP nanowires periodically ordered in arrays. The nanowires were grown by metal–organic vapor phase epitaxy on InP substrates, with either a single or 20 InAsP quantum discs embedded in the i-segment. By Zn compensation of the residual n-dopants in the i-segment, the room-temperature dark current is strongly suppressed to a level of pA/NW at 1 V bias. The low dark current is manifested in the spectrally resolved photocurrent measurements, which reveal strong photocurrent contributions from the InAsP quantum discs at room temperature with a threshold wavelength of about 2.0 μm and a bias-tunable responsivity reaching 7 A/W@1.38 μm at 2 V bias. Two different processing schemes were implemented to study the effects of radial self-gating in the nanowires induced by the nanowire/SiOx/ITO wrap-gate geometry. Summarized, our results show that properly designed axial InP/InAsP nanowire heterostructures are promising candidates for broadband photodetectors. © 2017 American Chemical Society.

  • 60.
    Kivisaari, Pyry
    et al.
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Berg, Alexander
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Karimi, Mohammad
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Storm, Kristian
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Limpert, Steven
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Oksanen, Jani
    Engineered Nanosystems Group, Aalto University, Aalto, Finland.
    Samuelson, Lars
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Pettersson, Håkan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab). Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Borgström, Magnus T.
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Optimization of Current Injection in AlGaInP Core−Shell Nanowire Light-Emitting Diodes2017Inngår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 17, nr 6, s. 3599-3606Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Core–shell nanowires offer great potential to enhance the efficiency of light-emitting diodes (LEDs) and expand the attainable wavelength range of LEDs over the whole visible spectrum. Additionally, nanowire (NW) LEDs can offer both improved light extraction and emission enhancement if the diameter of the wires is not larger than half the emission wavelength (λ/2). However, AlGaInP nanowire LEDs have so far failed to match the high efficiencies of traditional planar technologies, and the parameters limiting the efficiency remain unidentified. In this work, we show by experimental and theoretical studies that the small nanowire dimensions required for efficient light extraction and emission enhancement facilitate significant loss currents, which result in a low efficiency in radial NW LEDs in particular. To this end, we fabricate AlGaInP core–shell nanowire LEDs where the nanowire diameter is roughly equal to λ/2, and we find that both a large loss current and a large contact resistance are present in the samples. To investigate the significant loss current observed in the experiments in more detail, we carry out device simulations accounting for the full 3D nanowire geometry. According to the simulations, the low efficiency of radial AlGaInP nanowire LEDs can be explained by a substantial hole leakage to the outer barrier layer due to the small layer thicknesses and the close proximity of the shell contact. Using further simulations, we propose modifications to the epitaxial structure to eliminate such leakage currents and to increase the efficiency to near unity without sacrificing the λ/2 upper limit of the nanowire diameter. To gain a better insight of the device physics, we introduce an optical output measurement technique to estimate an ideality factor that is only dependent on the quasi-Fermi level separation in the LED. The results show ideality factors in the range of 1–2 around the maximum LED efficiency even in the presence of a very large voltage loss, indicating that the technique is especially attractive for measuring nanowire LEDs at an early stage of development before electrical contacts have been optimized. The presented results and characterization techniques form a basis of how to simultaneously optimize the electrical and optical efficiency of core–shell nanowire LEDs, paving the way to nanowire light emitters that make true use of larger-than-unity Purcell factors and the consequently enhanced spontaneous emission. © 2017American Chemical Society

  • 61.
    Ko, Byeonggeon
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Gao, Yang
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Monitoring Exchange Rates by Statistical Process Control2011Independent thesis Advanced level (degree of Master (One Year)), 10 poäng / 15 hpOppgave
    Abstract [en]

    The exchange rate market has traditionally played a key role in the financial market. The variation of the exchange rate which is called volatility is also an important feature for studying the exchange rate market because the increased volatility may have a negative effect on a nation's economy by increasing the uncertainty in the exchange market. In this paper the volatility of the exchange rate is considered by means of a Heterogeneous Autoregression Conditional Heteroskedastictity (HARCH) Model. It explains the volatility of the exchange rate market well. In addition, it is assumed that at a random time point a change of a parameter in the distribution of the random process underobservation may occur. Some methods such as the Shewhart method, the Culumative Sum Method (CUSUM) and the ExponentiallyWeighted Moving Average Method (EWMA) are investigated within the frames of this change-point problem. In order to evaluate them, Average Run Length (ARL) and Conditional Expected Delay (CED) will be used asperformance measures.

  • 62.
    Kudla, Jakub
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE). Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Monte Carlo SimulationsMethods in Pricing AmericanType Options2010Independent thesis Advanced level (degree of Master (One Year)), 15 poäng / 22,5 hpOppgave
    Abstract [en]

    The aim of this paper is to present simulation methods for the pricing of American financial instruments. Three methods are presented. Each differs from the others in it's approach to the problem and the method of finding a solution. We illustrate the variety of possible approaches that can be adopted when dealing with this complicated problem. The results of using these algorithms are compared with examples found in literature on the subject. We try to identify the factors that influence price estimators and provide some new results about the properties and distributions of those estimators. We show that even a simple variance reduction technique has a positive effect for these algorithms. The purpose of this paper is to present the effectiveness of a simulation method in pricing American options. This is contrary to the opinion often stated in articles and monographs that the simulation approach is not adequate for the task. We provide an overview and comparison of earlier methods proposed and follow this with an extended discussion. This paper sets the foundations for further research into use of these algorithms for multidimensional problems, where they may offer a substantial advantage over deterministic methods.

  • 63.
    Liu, Ruisheng
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab). Lund University, Lund, Sweden.
    Michalak, Lukasz
    Linnaeus University, Kalmar, Sweden.
    Canali, Carlo
    Linnaeus University, Kalmar, Sweden.
    Samuelson, Lars
    Lund University, Lund, Sweden.
    Pettersson, Håkan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Tunneling Anisotropic Magnetoresistance in Co/AlOx /Au Tunnel Junctions2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We observe spin-valve-like effects in nano-scaled thermally evaporated Co/AlOx/Au tunnel junctions. The tunneling magnetoresistance is anisotropic and depends on the relative orientation of the magnetization direction of the Co electrode with respect to the current direction. We attribute this effect to a two-step magnetization reversal and an anisotropic density of states resulting from spin-orbit interaction. The results of this study points to future applications of novel spintronics devices involving only one ferromagnetic layer.

  • 64.
    Liu, Ruisheng
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Pettersson, Håkan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Michalak, Lukasz
    Högskolan i Kalmar, Kalmar, Sweden.
    Canali, C. M.
    Linné Universitetet, Kalmar, Sweden.
    Samuelson, Lars
    Avd. f. Fasta Tillståndets Fysik, Lunds Universitet.
    Ferromagnetic single-electron transistors fabricated by atomic force microscopy2006Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We report on the fabrication and magneto-transport measurements of Ni/Au/Ni ferromagnetic single-electron transistors (F-SETs), fabricated by atomic force microscopy. By positioning a single Au disc (30 nm in diameter) into the gap between the Ni drain and source electrodes (of width 220 nm and 80 nm, respectively) step-by-step with Angstrom precision, and using plasma-processed NiOx as tunneling barriers, we can successfully fabricate F-SETs of high quality and substantial stability. The characteristic time interval of the device between two successive tunneling events is 10ps. The absence of any clear features in the transport related to the applied external magnetic field indicates that no spin-accumulation is maintained in the central Au disc. This interesting result indicates that the spin-relaxation time inside the central island should be shorter than 10ps. Based on these findings, we will discuss possible mechanisms of spin-relaxation in metal nano-structures triggered by spin-orbit interaction.

  • 65.
    Liu, Ruisheng
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Pettersson, Håkan
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Suyatin, D.
    Solid State Physics/ the Nanometer Structure Consortium, Lund University, Sweden.
    Michalak, L.
    Dept of Chemistry and Biomedical Sciences, Kalmar University, Sweden.
    Canali, C. M.
    Dept of Chemistry and Biomedical Sciences, Kalmar University, Sweden.
    Samuelson, L.
    Solid State Physics/ the Nanometer Structure Consortium, Lund University, Sweden.
    Nanoscaled Ferromagnetic Single-Electron Transistors2007Inngår i: 2007 7th IEEE International Conference on Nanotechnology - IEEE-NANO 2007, Proceedings, Piscataway, N.J.: IEEE Press, 2007, s. 420-421Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    We report on a summary of fabricating and characterizing nanoscaled ferromagnetic single-electron transistors (F-SETs). One type of device is assembled with an atomic force microscope. A single 30 nm Au disc, forming the central island of the transistor, is manipulated with Angstrom precision into the gap between plasma oxidized Ni source and drain electrodes which are designed with different geometries to facilitate magnetic moment reversal at different magnetic fields. The tunnel resistances can be tuned in real-time during the device fabrication by re-positioning the An disc. A second type of device with Co electrodes and a central Au island is fabricated using a high-precision alignment procedure invoked during e-beam writing. Both devices exhibit single-electron transistor characteristics at 4.2K. From magnetotransport measurements carried out at 1.7K, we found that it is more efficient to realize spin injection and detection in Co/Au/Co devices fabricated with the second technique. A maximum TMR of about 4% was observed in these devices.

  • 66.
    MALEKRAH, MEHDI
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Electrical and Optical Charactristics of InP Nanowire Photodetectors2010Independent thesis Advanced level (degree of Master (One Year)), 15 poäng / 22,5 hpOppgave
    Abstract [en]

    In this project Fourier Transform Infrared Spectroscopy is used to investigate a new kind of photodiode that is based on nanowires. The photo current and I-V curves for different temperatures, different applied biases, in darkness and illumination condition have been studied. The experiment was conducted in the temperature range from 78 K (-195ºC) to 300 K (27ºC). These photo diodes are designed to work on NIR wavelengths. The results show some excellent properties, such as high break down voltage, and that is an important advantage for photo detectors, low and constant reverse saturation current (Is). The results show some defects, most of them come from fabrication. The design of the sample is also discussed.

  • 67.
    Malmberg, Donald
    et al.
    MEFOS, Luleå, Sweden.
    Nilsson, Emil
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Using microwave technology to create a topographical image of the burden surface in a blast furnace2005Inngår i: Proceedings of 5th Ironmaking Conference, Buenos Aires: IAS , 2005, s. 213-220Konferansepaper (Fagfellevurdert)
  • 68.
    Maximchuk, Oleg
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Volkov, Yury
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Provisions estimation for portfolio of CDO in Gaussian financial environment2011Independent thesis Advanced level (degree of Master (One Year)), 10 poäng / 15 hpOppgave
    Abstract [en]

    The problem of managing the portfolio provisions is of very high importance for any financial institution. In this paper we provide both static and dynamic models of provisions estimation for the case when the decision about provisions is made at the first moment of time subject to the absence of information and for the case of complete and incomplete information. Also the hedging strategy for the case of the defaultable market is presented in this work as another tool of reducing the risk of default. The default time is modelled as a first-passage time of a standard Brownian motion through a deterministic barrier. Some methods of numerical provision estimation are also presented.

  • 69.
    Mezentsev, Anton
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Pomelnikov, Anton
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Ehrhardt, Matthias
    University Wuppertal, Wuppertal, Deutschland.
    Efficient Numerical Valuation of Continuous Installment Options2011Inngår i: Advances in Applied Mathematics and Mechanics, ISSN 2070-0733, E-ISSN 2075-1354, Vol. 3, nr 2, s. 141-164Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work we investigate the novel Kryzhnyi method for the numerical inverse Laplace transformation and apply it to the pricing problem of continuous installment options. We compare the results with the one obtained using other classical methods for the inverse Laplace transformation, like the Euler summation method or the Gaver-Stehfest method.

  • 70.
    Mironenko, Georgy
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Problem of hedging of a portfolio with a unique rebalancing moment2012Independent thesis Advanced level (degree of Master (One Year)), 10 poäng / 15 hpOppgave
    Abstract [en]

    The paper deals with the problem of finding an optimal one-time rebalancing strategy for the Bachelier model, and makes some remarks for the similar problem within Black-Scholes model. The problem is studied on finite time interval under mean-square criterion of optimality. The methods of the paper are based on the results for optimal stopping problem and standard mean-square criterion.

    The solution of the problem, considered in the paper, let us interpret how and - that is more important for us -when investor should rebalance the portfolio, if he wants to hedge it in the best way. 

  • 71.
    Nechaev, Mikhail
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    On Kalman Filter Application for Risk Estimation of Derivatives Portfolio2011Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Clearing houses or huge broker-dealers usually apply portfolio approach for the estimation of traders’ liabilities and restriction of their risk. It supposes that they analyse possible changes of portfolio’s value within a given time horizon. For clearing houses (in USA as well as in Europe) there exists a standard methodology called SPAN, developed by Chicago Mercantile Exchange, where scenario approach is implemented. Sometimes this approach fails due to the finite number (16) of considered scenarios. It seems that parametric approach provides better quality, but in this case man needs a fast algorithm for the Implied Volatility (IV) curve forecast. By now there exists an algorithm which uses a polynomial approximation for the IV curve merged with Kalman Filtering procedure as a forecasting tool. We develop a new model and provide statistical evidence which shows that approximation of IV curve by a special class of functions give better results. Correspondent analysis is based on the data from US options market.

  • 72.
    Nechaev, Mikhail
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    On risk-management features on exchange traded commodity derivatives market: Особенности управления рисками на биржевом срочном товарном рынке2011Inngår i: Securities Market (Рынок ценных бумаг), nr 4(409), s. 101-102Artikkel i tidsskrift (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    The paper present main features and problems of risk-managemnt on commodities market and provides a general description of risk management system for the exchange traded commodity derivatives. One of the main questions for such a system is the development of a risk control which also covers the delivery period, when real goods transferred from seller to buyer. We considr all main elements of the risk management system which provide a solution of the considered problems.

  • 73.
    Nechaev, Mikhail
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Dubinin, Vladimir
    Arbitrage Free Limit Order Pricing Model2010Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    It has been recognized by trading community for some time that the limit orderhas some option characteristics. Obviously, this is a special type of option as itis owned by the entire trading community as a whole. The exchanges recognizedthis fact by rewarding the limit orders with rebates. This paper is an attempt todetermine the faire value of this rebate, based on the absence of statistical arbitrage.

  • 74.
    Nechaev, Mikhail
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Tatsii, Vladimir
    Gazprombank OJSC, Moskva.
    On the dynamics of hydrocarbon commodity derivatives marketManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Dramatic changes on the international financial market, connected with the worldwide financial (and economic) crisis, originated enormous number of recipes for its negative circumstances overcoming and formation of “extremely new” conditions and rules for performing of financial activities, which can make “prices manipulation” absolutely impossible. In particular, and this is especially important for Russia, great attention is devoted to the problem of pricing on the oil and natural gaz markets, because stability and predictability for the hydrocarbons prices are one of the main conditions for the world economics development.The arguments presented in the paper demonstrate the necessity not for the prices regulation, which is evidently ineffective, but the necessity of the rules for the whole process of the price negotiation and evaluation, the necessity of development of corresponding information environment, which can provide “fair prices” on the hydrocarbons market.

  • 75.
    Nilsson, Bertil
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Hansbo, Peter
    Chalmers, Matematiska vetenskaper.
    Weak coupling of a Reynolds model and a Stokes model for hydrodynamic lubrication2011Inngår i: International Journal for Numerical Methods in Fluids, ISSN 0271-2091, E-ISSN 1097-0363, Vol. 66, nr 6, s. 730-741Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Reynolds model is a reduced Stokes model, valid for narrow lubrication regions. In order to be able to handle locally non-narrow regions such as pits or grooves, often displaying rapid geometrical variations, there is a need to be able to transit to the more accurate Stokes model. A fundamental problem is how to couple the two models in a numerical simulation, preferably allowing for different meshes in the different domains. In this paper, we present a weak coupling method for Reynolds and Stokes models for lubrication computations, including the possibility of cavitation in the different regions. The paper concludes with a numerical example.

  • 76.
    Nilsson, Emil
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Sensor Platform for 3D Microwave Interferometry Imaging: Theory and Experiments2006Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 77.
    Nilsson, Emil
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Bååth, Lars
    Agellis Group AB, Lund.
    Radar Interferometric Measurements With a Planar Patch Antenna Array2007Inngår i: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 7, nr 7, s. 1025-1031Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A planar patch antenna array has been made for radar interferometry. The antenna array consists of 32 rectangular patches on a ceramic loaded teflon substrate. The patches are individually coupled to the microwave electronics in two orthogonal circular polarizations. The radar interferometer is intended for topographic imaging in industrial environment, in this case, a blast furnace producing hot metal for the steel and metal industry. Ordinary imaging techniques with IR or visible radiation are not possible to use due to high temperatures, scattering from dust and particles. A model of blast furnace burden material surface was measured and detected.

  • 78.
    Nilsson, Emil
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Linnér, Peter
    Department of Physics, Chalmers University of Technology, Gothenburg SE-41296, Sweden.
    Sikö, Arne
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE).
    Bilstrup, Urban
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
    Wiberg, Per-Arne
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
    A new CMOS radio for low power RFID applications2010Inngår i: Proceedings of 2010 IEEE International Conference on RFID-Technology and Applications : June 17-19, 2010 : Dong Fang Hotel, Guangzhou, China., Piscataway, N.J.: IEEE Press, 2010, s. 106-111Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A novel radio receiver circuit, functioning as a tuned active, detecting antenna, is described. The receiver is suggested to be part of a new radio system with the potential of competing with the range capability of active RFID-tags and, through its low power and long lifetime, with passive RFID-tags. The circuit is outlined and the functionality is verified by simulations and measurements.

    A 24 MHz discrete prototype showed better than -70 dBm sensitivity and 5 kHz bandwidth, with a power consumption of 102 μW. Simulations of a monolithic implementation were performed at 2.5 GHz. The detector is modeled by using 180 nm CMOS transistors. In simulations the power consumption for the detector is below 125 μW at a sensitivity of -83 dBm and a bandwidth of 9 MHz.

    Our conclusion is that this novel simple circuit architecture is well suited for monolithic implementation of a low power transceiver.

  • 79.
    Nilsson, Emil
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Malmberg, Donald
    MEFOS, Luleå, Sweden.
    Using microwave interferometry to improve the blast furnace operation2008Inngår i: SCANMET III: 3rd International Conference on Process Development in Iron and Steelmaking : 8-11 June 2008, Luleå, Sweden : Nordkalotten Hotel & Conference. Vol. 1., Luleå: MEFOS , 2008, s. 617-626Konferansepaper (Fagfellevurdert)
    Abstract [en]

    There are many known technologies that can be used to monitor surfaces, but the most of them requires a transparent environment to be functional. In the Blast Furnace where the environment is full of dust and fume at high temperatures those technologies are not applicable.

    With a functional technology in such an environment the burden surface could be analysed and monitored, which in its extension would lead to a way to control the charging operation in the BF and thus a better use of raw material and also a better gas utilization.

    In this paper we will discuss the use of microwave technology as one technology with the potential to create a topographical image of the burden surface in the Blast Furnace during operation.

  • 80.
    Nilsson, Emil
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Nilsson, Björn
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Inbyggda system (CERES).
    Järpe, Eric
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    A Pharmaceutical Anti-counterfeiting Method Using Time Controlled Numeric Tokens2011Inngår i: 2011 IEEE International Conference on RFID-Technologies and Applications, Piscataway, NJ: IEEE Press, 2011, s. 335-339Konferansepaper (Fagfellevurdert)
    Abstract [en]

    An anti-counterfeit and authentication method usingtime controlled numeric tokens enabling a secure logistic chain ispresented. Implementation of the method is illustrated with apharmaceutical anti-counterfeit system. The method uses activeRFID technology in combination with product seal. Authenticityis verified by comparing time controlled ID-codes, i.e. numerictokens, stored in RFID tags and by identical numeric tokensstored in a secure database. The pharmaceutical products areprotected from the supplier to the pharmacist, with thepossibility to extend the authentication out to the end customer.The ability of the method is analyzed by discussion of severalpossible scenarios. It is shown that an accuracy of 99.9% tellingthe customer she has an authentic product is achieved by the useof 11-bit ID-code strings.

  • 81.
    Nilsson, Emil
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Svensson, Christer
    ISY, Linköping University, Linköping, Sweden.
    Envelope Detector Sensitivity and Blocking Characteristics2011Inngår i: 2011 20th European Conference on Circuit Theory and Design (ECCTD), Piscataway, NJ: IEEE Press, 2011, s. 773-776, artikkel-id 6043845Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper presents analytical expressions for the sensitivity of a low power envelope detector driven by a weak RF signal in the presence of a blocking signal. The envelope detector has been proposed for low power Wake-Up radios in applications such as RFID and wireless sensor systems. The theoretical results are verified with simulations of a modern short channel MOS transistor in a commonly used circuit topology. A discussion around a tutorial example of a radio frontend, consisting of an LNA and a detector, is presented. It is shown that the sensitivity of a low power envelope detector can reach -62 dBm with a low power LNA and in presence of a CW blocker. © 2011 IEEE.

  • 82.
    Nilsson, Emil
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Svensson, Christer
    Department of Electrical Engineering (ISY), Linköping University, Linköping, Sweden .
    Power Consumption of Integrated Low-Power Receivers2014Inngår i: IEEE Journal on Emerging and Selected Topics in Circuits and Systems, ISSN 2156-3357, Vol. 4, nr 3, s. 273-283Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    With the advent of Internet of Things (IoT) it has become clear that radio-frequency (RF) designers have to be aware of power constraints, e.g., in the design of simplistic ultra-low power receivers often used as wake-up radios (WuRs). The objective of this work, one of the first systematic studies of power bounds for RF-systems, is to provide an overview and intuitive feel for how power consumption and sensitivity relates for low-power receivers. This was done by setting up basic circuit schematics for different radio receiver architectures to find analytical expressions for their output signal-to-noise ratio including power consumption, bandwidth, sensitivity, and carrier frequency. The analytical expressions and optimizations of the circuits give us relations between dc-energy-per-bit and receiver sensitivity, which can be compared to recent published low-power receivers. The parameter set used in the analysis is meant to reflect typical values for an integrated 90 nm complementary metal-oxide-semiconductor fabrication processes, and typical small sized RF lumped components.

  • 83.
    Nilsson, Emil
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Svensson, Christer
    Linkoping Univ, Dept Elect Engn ISY, SE-58183 Linkoping, Sweden..
    Ultra Low Power Wake-Up Radio Using Envelope Detector and Transmission Line Voltage Transformer2013Inngår i: IEEE JOURNAL ON EMERGING AND SELECTED TOPICS IN CIRCUITS AND SYSTEMS, ISSN 2156-3357, Vol. 3, nr 1, s. 5-12Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An ultra-low power wake-up radio receiver using no oscillators is described. The radio utilizes an envelope detector followed by a baseband amplifier and is fabricated in a 130-nm complementary metal-oxide-semiconductor process. The receiver is preceded by a passive radio-frequency voltage transformer, also providing 50 Omega antenna matching, fabricated as transmission lines on the FR4 chip carrier. A sensitivity of -47 dBm with 200 kb/s on-off keying modulation is measured at a current consumption of 2.3 mu A from a 1 V supply. No trimming is used. The receiver accepts a dBm continuous wave blocking signal, or modulated blockers 6 dB below the sensitivity limit, with no loss of sensitivity.

  • 84.
    Nilsson, Pernilla
    et al.
    Högskolan i Halmstad, Akademin för lärande, humaniora och samhälle, Forskning om utbildning och lärande inom lärarutbildningen (FULL).
    Pendrill, Ann-Marie
    Institutionen för fysik, Göteborgs Universitet.
    Pettersson, Håkan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    En jämförande studie av olika elevgruppers förståelse av accelerationsbegreppet2005Konferansepaper (Fagfellevurdert)
    Abstract [sv]

    Syfte

    Begreppet acceleration har visat sig vara ett svårt begrepp att förstå, även i högre kurser i fysik. Kopplingen mellan acceleration och kraft är ofta oklar. Studenterna har  svårt att förstå hur krafter verkar, eller vilka krafter som finns. De blandar t.ex. ofta in tröghets-krafter. I detta konferensbidrag diskuterar vi resultaten från en jämförande studie av hur 11-åringar, lärarstudenter F-5 och teknisk fysikstudenter (civilingenjörsstudenter) diskuterar och resonerar runt begreppet acceleration. Empirin bygger på fria gruppdiskussioner och intervjuer beträffande accelerationsbegreppet vid experiment i klassrummet och på nöjesparken Liseberg. I denna studie söker vi svar på frågor som: hur påverkas resonemanget och språket av förkunskaper och tidigare erfarenheter av fysik? Vilken inverkan har den lärandekontext de befinner sig i? Hur använder de olika elevgrupperna vardagsspråk kontra vetenskapligt språk då de beskriver begreppet acceleration? Vi är också intresserade av att se hur de tre elevgrupperna relaterar begreppet acceleration till begreppet kraft och om det finns det ett mönster beträffande missuppfattningar av accelerationsbegreppet och kraftbegreppet.

    Bakgrund och teoretisk utgångspunkt

    Gunstone & Watts (i Driver mfl, 1985) har sammanställt några av barns grundläggande idéer och tankar om relationen mellan kraft och rörelse. I dessa studier framkommer det att vanliga  missuppfattningar är att det inte kan finnas någon kraft utan rörelse och att kraft har att göra med levande varelser.

    Studien bygger på ett perspektiv på lärande där kunskap fördjupas i diskurser och där språket är ett viktigt redskap för att utveckla och kommunicera kunskap (Vygotsky, 1934/1986; Dyste, 2003). I sina diskussioner visar barnen och studenterna på ett resonemang där flera fysikaliska termer och begrepp utvecklas, förklaras, exemplifieras och kopplas till ett vardagssammanhang.

    Forskning visar att elever ofta känner sig osäkra inför den naturvetenskapliga diskursen (Schoultz, 2000). De har svårigheter att använda naturvetenskapliga termer och begrepp i samtal och texter. Alltför ofta använder de endast termen för ett fenomen som en korrekt förklaring. För att förstå naturvetenskapen räcker det inte att endast ytligt känna till dessa termer och begrepp utan man måste ha en djupare förståelse av dessa, såväl som en förståelse av hur de är sammanlänkade till en enhetlig begreppsbild.

    I det objektiva naturvetenskapliga språket använder man ett begreppssystem som inte refererar till mänskliga upplevelser. Genom att koppla in de mäskliga upplevelserna av olika fenomen kan begreppen få en ny dimension som kan underlätta förståelsen och inlärningsprocessen.

    Empiriskt material

    Samtliga elevgrupper i denna studie har diskuterat begreppet acceleration både med hjälp av olika klassrumsexperiment, och i samband med olika åkattraktioner på Liseberg. Därför består det empiriska materialet av video och kassettbandinspelningar av gruppdiskussioner vid klassrumsexperiment, men även av diskussioner och spontana intervjuer och videofilmer från Liseberg.

  • 85.
    Nowzari, Ali
    et al.
    Division of Solid State Physics and The Nanometer Structure Consortium, Lund University, Sweden.
    Heurlin, Magnus
    Division of Solid State Physics and The Nanometer Structure Consortium, Lund University, Sweden.
    jain, Vishal
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab). Division of Solid State Physics and The Nanometer Structure Consortium, Lund University, Sweden.
    Storm, Kristian
    Division of Solid State Physics and The Nanometer Structure Consortium, Lund University, Sweden.
    Hosseinnia, Ali
    Division of Solid State Physics and The Nanometer Structure Consortium, Lund University, Sweden.
    Anttu, Nicklas
    Division of Solid State Physics and The Nanometer Structure Consortium, Lund University, Sweden.
    Borgström, Magnus T.
    Division of Solid State Physics and The Nanometer Structure Consortium, Lund University, Sweden.
    Pettersson, Håkan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab). Division of Solid State Physics and The Nanometer Structure Consortium, Lund University, Sweden.
    Samuelson, Lars
    Division of Solid State Physics and The Nanometer Structure Consortium, Lund University, Sweden.
    A Comparative Study of Absorption in Vertically and Laterally Oriented InP Core–Shell Nanowire Photovoltaic Devices2015Inngår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 15, nr 3, s. 1809-1814Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have compared the absorption in InP core-shell nanowire p-i-n junctions in lateral and vertical orientation. Arrays of vertical core-shell nanowires with 400 nm pitch and 280 nm diameter, as well as corresponding lateral single core-shell nanowires, were configured as photovoltaic devices. The photovoltaic characteristics of the samples, measured under 1 sun illumination, showed a higher absorption in lateral single nanowires compared to that in individual vertical nanowires, arranged in arrays with 400 nm pitch. Electromagnetic modeling of the structures confirmed the experimental observations and showed that the absorption in a vertical nanowire in an array depends strongly on the array pitch. The modeling demonstrated that, depending on the array pitch, absorption in a vertical nanowire can be lower or higher than that in a lateral nanowire with equal absorption predicted at a pitch of 510 nm for our nanowire geometry. The technology described in this Letter facilitates quantitative comparison of absorption in laterally and vertically oriented core-shell nanowire p-i-n junctions and can aid in the design, optimization, and performance evaluation of nanowire-based core-shell photovoltaic devices. © 2014 American Chemical Society.

  • 86.
    Park, Min-Su
    et al.
    Center for Optoelectronic Convergence Systems, KIST (Korean Institute of Science and Technology), Seoul, Republic of Korea.
    Jain, Vishal
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab). Lund Univ, Solid State Phys & Nanometer Struct Consortium, Lund, Sweden.
    Lee, E.H.
    Center for Optoelectronic Convergence Systems, KIST (Korean Institute of Science and Technology), Seoul, Republic of Korea.
    Kim, S.H.
    Center for Optoelectronic Convergence Systems, KIST (Korean Institute of Science and Technology), Seoul, Republic of Korea.
    Pettersson, Håkan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab). Lund Univ, Solid State Phys & Nanometer Struct Consortium, Lund, Sweden.
    Wang, Q
    Acreo Swedish ICT AB, Electrum Lab Nano & Microtechnol Fab, Kista, Sweden.
    Song, JD
    Center for Optoelectronic Convergence Systems, KIST (Korean Institute of Science and Technology), Seoul, Republic of Korea.
    Choi, WJ
    Center for Optoelectronic Convergence Systems, KIST (Korean Institute of Science and Technology), Seoul, Republic of Korea.
    InAs/GaAs p-i-p quantum dots-in-a-well infrared photodetectors operating beyond 200 K2014Inngår i: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 50, nr 23, s. 1731-1733Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High-temperature operating performance of p-i-p quantum dots-in-awell infrared photodetectors (QDIPs) is successfully demonstrated. The optically active region consists of 10 layers of p-doped selfassembled InAs quantum dots (QDs) asymmetrically positioned in In0.15Ga0.85As quantum wells (QWs). The dark current is suppressed by an incorporated superlattice (SL) structure composed of 10 pairs of AlGaAs/GaAs heterostructure. The very low recorded dark current makes the fabricated p-i-p QDIPs suitable for high-temperature operation. The measured photoresponse reveals broad mid-wave infrared (MWIR) detection up to 200 K. © The Institution of Engineering and Technology 2014

  • 87.
    Paschoal Jr., Waldomiro
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab). Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Kumar, Sandeep
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab). Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Jacobsson, Daniel
    Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Johannes, Andreas
    Institute for Solid State Physics, Jena University, Jena, Germany.
    Jain, Vishal
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab). Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Canali, Carlo M.
    Department of Physics and Electrical Engineering, Linneaus University, Kalmar, Sweden.
    Pertsova, Anna
    Department of Physics and Electrical Engineering, Linneaus University, Kalmar, Sweden.
    Ronning, Carsten
    Institute for Solid State Physics, Jena University, Jena, Germany.
    Dick, Kimberly A.
    Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Samuelson, Lars
    Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Pettersson, Håkan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Magnetoresistance in Mn ion-implanted GaAs:Zn nanowires2014Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 104, nr 15, artikkel-id 153112Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have investigated the magnetoresistance (MR) in a series of Zn doped (p-type) GaAs nanowires implanted with different Mn concentrations. The nanowires with the lowest Mn concentration (~0.0001%) exhibit a low resistance of a few kΩ at 300K and a 4% positive MR at 1.6K, which can be well described by invoking a spin-split subband model. In contrast, nanowires with the highest Mn concentration (4%) display a large resistance of several MΩ at 300K and a large negative MR of 85% at 1.6K. The large negative MR is interpreted in terms of spin-dependent hopping in a complex magnetic nanowire landscape of magnetic polarons, separated by intermediate regions of Mn impurity spins. Sweeping the magnetic field back and forth for the 4% sample reveals a hysteresis that indicates the presence of a weak ferromagnetic phase. We propose co-doping with Zn to be a promising way to reach the goal of realizing ferromagnetic Ga1-xMnxAs nanowires for future nanospintronics. © 2014 AIP Publishing LLC.

  • 88.
    Pettersson, Håkan
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab). Nanometer Structure Consortium, Lund University.
    Nanoscale devices for future opto-and magnetoelectronics2008Konferansepaper (Fagfellevurdert)
  • 89.
    Pettersson, Håkan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Nanoscale devices for future optoelectronics2012Konferansepaper (Fagfellevurdert)
  • 90.
    Pettersson, Håkan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Nanowire Infrared Photodetectors2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Over the last two decades there has been a dramatic increase in research activities related to semiconductor nanowires (NWs) due to their exciting prospects for implementation of novel high-performance electronics and photonics compatible with main-stream silicon technology.  In this talk, I will give an overview of our research efforts on infrared photodetectors based on InP/InAsP semiconductor NWs. I will discuss growth, processing and characterization of both single NW devices and large square millimeter array devices comprising millions of NWs connected in parallel. The electrical data generally display excellent rectifying behavior with small leakage currents. From optical measurements, combined with modeling, we conclude that the photocurrent generation depends strongly on the geometry and doping of the NW devices. Properly designed, the absorption of IR radiation in array devices can be significantly enhanced by nanophotonic resonances induced by the geometry and spatially matched to the position of the embedded p-n junctions in the NWs yielding high-efficiency photovoltaics. We have also carried out in-depth studies of InP NW arrays with multiple enclosed axial InAsP quantum wells for broadband and thermal imaging applications. Finally, I will discuss our recent research efforts targeting single InP/InAsP NW avalanche photodetectors with separate absorption and multiplication regions. The presented photodetectors can potentially be grown on cheap silicon substrates due to the small footprint of the NWs. Successfully developed, novel low-cost and high-performance detector families for optical communication, thermal imaging and solar cell applications can be realized.

  • 91.
    Pettersson, Håkan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Nanowire-based Infrared Photodetectors2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this talk, I will discuss electrical and optical properties of infrared photodetectors/solar cells based on  square millimeter ensembles (> 1 million) of vertically processed InP/InAsP semiconductor nanowires grown on InP substrates.

    To investigate current generation processes in InP p+-i-n photodetectors/solar cells, we fabricated a sample series where the p+-segment length was varied, as well as optimized solar cells with 9.3 % efficiency with similar design. The electrical data generally display excellent rectifying behavior with small leakage currents. From spectrally resolved photocurrent measurements, we conclude that the photocurrent generation process depends strongly on the p+-segment length. Without p+-segment, photogenerated carriers funneled from the substrate into the NWs contribute significantly to the photocurrent. Adding a p+-segment decouples the substrate and shifts the depletion region, and collection of photogenerated carriers, to the nanowires, in agreement with sophisticated theoretical modeling. In optimized solar cells, clear spectral signatures of interband transitions in the ZB and WZ InP layers of the mixed-phase i-segments are observed. Complementary measurements of the dependence of the photocurrent on angle of incidence and polarization, as well as electroluminescence, support our interpretations.

    I will also discuss large area photoconductors based on n-i-n InP nanowires with axial InAsP quantum wells embedded in the i-region. Spectrally resolved photocurrent measurements and photoluminescence measurements reveal clear interband transitions both in the InP segments and InAsP quantum wells. By increasing the number of incorporated quantum wells, one important goal is to enhance the contribution from intersubband transitions in the quantum wells thereby facilitating detectors/focal plane arrays with a broad detection window from near-infrared to long-wavelength infrared regions.

    Finally, I will briefly mention efforts targeting large area p+-n-n-  InP/InAsP avalanche nanowire photodiodes with low electric field in the low-bandgap InAsP segment and high electric field in the InP multiplication region. Besides clear interband photocurrent signals from the InP and InAsP regions, a strong bias-dependent blueshifted photocurrent peak appears at forward bias offering an interesting novel tunability of the spectral window.

    The presented nanowire-based photodetectors can potentially be grown on silicon substrates due to the small footprint of the nanowires. Successfully developed, novel detector families of low-cost, high performance broadband detectors for optical communication, thermal imaging and solar cell applications can thus be realized.

  • 92.
    Pettersson, Håkan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Nanowire-based infrared photodetectors2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this talk, I will discuss electrical and optical properties of infrared photodetectors/solar cells based on square millimeter ensembles (> 1 million) of vertically processed InP/InAsP semiconductor nanowires grown on InP substrates.

       To investigate current generation processes in InP p+-i-n photodetectors/solar cells, we fabricated a sample series where the p+-segment length was varied, as well as optimized solar cells with 9.3 % efficiency with similar design. The electrical data generally display excellent rectifying behavior with small leakage currents. From spectrally resolved photocurrent measurements, we conclude that the photocurrent generation process depends strongly on the p+-segment length. Without p+-segment, photogenerated carriers funneled from the substrate into the NWs contribute significantly to the photocurrent. Adding a p+-segment decouples the substrate and shifts the depletion region, and collection of photogenerated carriers, to the nanowires, in agreement with sophisticated theoretical modeling. In optimized solar cells, clear spectral signatures of interband transitions in the ZB and WZ InP layers of the mixed-phase i-segments are observed. Complementary measurements of the dependence of the photocurrent on angle of incidence and polarization, as well as electroluminescence, support our interpretations.

        I will also discuss large area photoconductors based on n+-i- n+ InP NWs with embedded InAsP QWs grown in axial geometry on InP substrates. Spectrally resolved photocurrent measurements and photoluminescence measurements reveal clear interband transitions both in the InP segments and InAsP quantum wells. By increasing the number of incorporated quantum wells in the nanowires, the contribution from intersubband transitions in the quantum wells can be enhanced thereby facilitating detectors/focal plane arrays with a broad detection window from near-infrared to long-wavelength infrared regions.

    Finally, I will briefly mention efforts targeting large area p+-n-n-  InP/InAsP avalanche nanowire photodiodes with low electric field in the low-bandgap InAsP segment and high electric field in the InP multiplication region. Besides clear interband photocurrent signals from the InP and InAsP regions, a strong bias-dependent blueshifted photocurrent peak appears at forward bias offering an interesting novel tunability of the spectral window.

    The presented nanowire-based photodetectors can potentially be grown on silicon substrates due to the small footprint of the nanowires. Successfully developed, novel detector families of low-cost, high performance broadband detectors for optical communication, thermal imaging and solar cell applications can thus be realized.

  • 93.
    Pettersson, Håkan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab). Lund University, Lund, Sweden.
    Physics and Technology of Nanowire Photodetectors2017Inngår i: 2017 Technical Summaries: OPTP, 2017, s. 279-279Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Over the last two decades there has been a dramatic increase in research activities related to semiconductor nanowires (NWs) due to their exciting prospects for implementation of novel high-performance electronics and photonics compatible with main-stream silicon technology.  In this talk, I will give an overview of our research efforts on infrared photodetectors based on InP/InAsP semiconductor NWs. I will discuss growth, processing and characterization of both single NW devices and large square millimeter array devices comprising millions of NWs connected in parallel. The electrical data generally display excellent rectifying behavior with small leakage currents. From optical measurements, combined with modeling, we conclude that the photocurrent generation depends strongly on the geometry and doping of the NW devices. Properly designed, the absorption of IR radiation in array devices can be significantly enhanced by nanophotonic resonances induced by the geometry and spatially matched to the position of the embedded p-n junctions in the NWs yielding high-efficiency photovoltaics. We have also carried out in-depth studies of InP NW arrays with multiple enclosed axial InAsP quantum wells for broadband and thermal imaging applications. Finally, I will discuss our recent research efforts targeting single InP/InAsP NW avalanche photodetectors with separate absorption and multiplication regions. The presented photodetectors can potentially be grown on cheap silicon substrates due to the small footprint of the NWs. Successfully developed, novel low-cost and high-performance detector families for optical communication, thermal imaging and solar cell applications can be realized.

  • 94.
    Pettersson, Håkan
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Bordag, Michael
    Leipzig University, Leipzig, Germany.
    Ribayrol, Aline
    Lund University, Lund, Sweden.
    Conache, Gabriela
    Lund University, Lund, Sweden.
    Fröberg, Linus
    Lund University, Lund, Sweden.
    Samuelson, Lars
    Lund University, Lund, Sweden.
    Montelius, Lars
    Lund University, Lund, Sweden.
    Shear stress measurements on InAs nanowires by AFM manipulation2007Inngår i: Bulletin of the American Physical Society, ISSN 0003-0503, Vol. 52, nr 1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we report on a novel approach to measure shear stress between elastic nanowires and a SiO2 surface. The method is based on the fact that the curvature of an elastically deformed nanowire pinned to a flat surface contains information about the maximal static friction force, i.e., the shear stress between the wire and the surface. At rest, the deformed wire is kept in equilibrium by counterbalancing static friction forces and restoring elastic forces. In the present work, InAs nanowires are bent in a controlled manner using the tip of an atomic force microscope (AFM). After the manipulation, the curvature of the most bent state can be determined from AFM micrographs. Assuming bulk values for the Young’s modulus, the shear stress can be obtained from straight- forward analyses according to standard theory of elasticity. 

  • 95.
    Pettersson, Håkan
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Conache, Gabriela
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Gray, Struan M.
    Lund University, Lund, Sweden.
    Bordag, Michael
    Leipzig University, Leipzig, Germany.
    Ribayrol, Aline
    Solid State Physics, Lund University, Lund, Sweden.
    Fröberg, Linus
    Solid State Physics, Lund University, Lund, Sweden.
    Samuelson, Lars
    Solid State Physics, Lund University, Lund, Sweden.
    Montelius, Lars
    Solid State Physics, Lund University, Lund, Sweden.
    Friction measurements on InAs NWs by AFM manipulation2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We discuss a new approach to measure the friction force between elastically deformed nanowires and a surface. The wires are bent, using an AFM, into an equilibrium shape determined by elastic restoring forces within the wire and friction between the wire and the surface. From measurements of the radius of curvature of the bent wires, elasticity theory allows the friction force per unit length to be calculated. We have studied friction properties of InAs nanowires deposited on SiO2, silanized SiO2 and Si3N4 substrates. The wires were typically from 0.5 to a few microns long, with diameters varying between 20 and 80 nm. Manipulation is done in a `Retrace Lift' mode, where feedback is turned off for the reverse scan and the tip follows a nominal path. The effective manipulation force during the reverse scan can be changed by varying an offset in the height of the tip over the surface. We will report on interesting static- and sliding friction experiments with nanowires on the different substrates, including how the friction force per unit length varies with the diameter of the wires.

  • 96.
    Pettersson, Håkan
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Conache, Gabriela
    Lund University, Solid State Physics, Box 118, 22100, Lund, Sweden.
    Gray, Struan
    Avd. f. Fasta Tillståndets Fysik, Lunds Universitet, Sweden.
    Ribayrol, Aline
    Avd. f. Fasta Tillståndets Fysik, Lunds Universitet, Sweden.
    Fröberg, Linus
    Avd. f. Fasta Tillståndets Fysik, Lunds Universitet, Sweden.
    Samuelson, Lars
    Avd. f. Fasta Tillståndets Fysik, Lunds Universitet, Sweden.
    Montelius, Lars
    Avd. f. Fasta Tillståndets Fysik, Lunds Universitet, Sweden.
    Nanowire friction with an applied bias2010Inngår i: Bulletin of the American Physical Society: APS March Meeting 2010, Volume 55, Number 2, American Physical Society , 2010Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Recently, we have shown how the friction experienced by nanowires pushed by an AFM tip can be determined by measuring their radius of curvature after manipulation [1]. It is of fundamental interest to know whether the wires behave like macroscopic objects, or if they are more like true atomic-scale point contacts where friction becomes independent of the applied normal force. Here we study how the friction between InAs nanowires and a SiN layer on conductive silicon varies when a DC voltage is applied. The tip charges the capacitor formed by the wire and the silicon back contact, causing attractive Coulomb forces and so increasing the contact pressure. A monotonic increase of the sliding friction with voltage was observed. This implies that the friction increases with the normal force and that this mesoscopic system behaves more like a macroscopic contact, despite being only nanometers in size in the direction of motion.

  • 97.
    Pettersson, Håkan
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Höglund, Linda
    Acreo AB, Electrum 236, S-16440 Kista, Sweden.
    Karlsson, Fredrik
    Department of Physics, Chemistry and Biology (IFM), Linköping University, S-58183 Linköping, Sweden.
    Holtz, Per-Olof
    Department of Physics, Chemistry and Biology (IFM), Linköping University, S-58183 Linköping, Sweden.
    Wang, Qin
    Acreo AB, Electrum 236, S-16440 Kista, Sweden.
    Almqvist, Susanne
    Acreo AB, Electrum 236, S-16440 Kista, Sweden.
    Asplund, Carl
    IRnova, Electrum 236, S-16440 Kista, Sweden.
    Malm, Hedda
    IRnova, Electrum 236, S-16440 Kista, Sweden.
    Petrini, Erik
    Acreo AB, Electrum 236, S-16440 Kista, Sweden.
    Pistol, Mats-Erik
    Solid State Physics and the Nanometer Consortium, Lund University, BOX 118, S-22100 Lund, Sweden.
    Andersson, Jan
    Acreo AB, Electrum 236, S-16440 Kista, Sweden.
    Quantum Dots-in-a-Well Infrared Photodetectors-Electronic Structure and Optical Properties2010Inngår i: Bulletin of American Physical Society: APS March Meeting 2010, Volume 55, Number 2, American Physical Society , 2010Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Quantum dots-in-a-well (DWELL) infrared photodetectors is a new class of nanophotonic devices with the potential of significantly increasing the performance and reducing the cost of infrared detectors. Here we present a comprehensive study of DWELL photodetector structures using a variety of optical techniques (PL, PLE, and PC). Complementary tunnel capacitance measurements support the electronic structure obtained from the optical measurements. A detailed energy level scheme based on the experimental findings is presented and compared to theoretical modeling. The presented work show the importance of combining different electrical and optical techniques to obtain a consistent model of complicated quantum structures which is crucial for the development of future nanophotonic devices.

  • 98.
    Pettersson, Håkan
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Liu, Ruisheng S.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Suyatin, Dmitry
    Avdelningen för Fasta Tillståndets Fysik (FTF), Lunds Universitet.
    Samuelson, Lars
    Avdelningen för Fasta Tillståndets Fysik (FTF), Lunds Universitet.
    Assembling ferromagnetic single-electron transistors by atomic force microscopy2008Inngår i: Nanostructures in electronics and photonics / [ed] Rahman, Faiz, Singapore: Pan Stanford Publishing, 2008, s. 29-40Kapittel i bok, del av antologi (Fagfellevurdert)
  • 99.
    Pettersson, Håkan
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS). Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Liu, Ruisheng S.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab). Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Suyatin, Dmitry
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Samuelson, Lars
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Assembling ferromagnetic single-electron transistors with atomic force microscopy2008Inngår i: Nanostructures in Electronics and Photonics / [ed] Faiz Rahman, London: Pan Stanford Publishing, 2008, s. 29-40Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    Ferromagnetic Single Electron Transistors (F-SETs) comprise ferromagnetic electrodes connected to a ferromagnetic- or non-magnetic central island via tunnel barriers. These devices are important for studies of spin-transport physics in confined structures. Here we describe the development of a novel type of AFMassembled nano-scale F-SETs suitable for spin-transport investigations at temperatures above 4.2 K. The ingenious fabrication technique means that their electrical characteristics can be tuned in real-time during the fabrication sequence by re-positioning the central island with Ångström precision. © 2008 by Pan Stanford Publishing Pte. Ltd. All rights reserved.

  • 100.
    Pettersson, Håkan
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Suyatin, Dmitry
    Solid State Physics/The Nanometer Structure Consortium, Lund University, Box 118, S-221 00, Lund, Sweden.
    Trägårdh, Johanna
    Solid State Physics/The Nanometer Structure Consortium, Lund University, Box 118, S-221 00, Lund, Sweden.
    Messing, Maria
    Solid State Physics/The Nanometer Structure Consortium, Lund University, Box 118, S-221 00, Lund, Sweden.
    Wagner, Jakob
    Materials Chemistry, Lund University, Box 124, S-221 00 Lund, Sweden.
    Montelius, Lars
    Solid State Physics/The Nanometer Structure Consortium, Lund University, Box 118, S-221 00, Lund, Sweden.
    Samuelson, Lars
    Solid State Physics/The Nanometer Structure Consortium, Lund University, Box 118, S-221 00, Lund, Sweden.
    Nano-Schottky contacts realized by bottom-up technique2010Inngår i: Bulletin of American Physical Society: APS March Meeting 2010, Volume 55, Number 2, American Physical Society , 2010Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Here we present a comprehensive study of a rectifying nano-Schottky contact formed at the interface between a gold catalytic particle and an epitaxially grown GaInAs/InAs nanowire. Selective electrical connections formed by electron beam lithography to the catalytic particle on one side, and to the InAs segment on the other side allowed electrical and optical characterization of the formed Schottky junction. From IV measurements taken at different temperatures we have deduced the Schottky barrier height and the height of the barrier formed in the graded GaInAs nanowire segment. The IV characteristics measured under laser stimulation showed that the device can be used as a unipolar photodetector with extremely small detection volume and potentially ultra fast response.

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