hh.sePublications
Change search
Refine search result
1 - 16 of 16
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Bååth, Lars
    et al.
    Halmstad University, School of Business, Engineering and Science, Mechanical Engineering and Industrial Design (MTEK), Fotonik.
    Rosén, Bengt-Göran
    Halmstad University, School of Business, Engineering and Science, Mechanical Engineering and Industrial Design (MTEK), Functional Surfaces.
    Towards New Interferometer Technology for Surface Metrology2012In: Proceedings of the 12th International Conference of the European Society for Precision Engineering and Nanotechnology: June 4th - 7th [8th] 2012, Stockholm, Sweden. Vol. 1 / [ed] P. Shore, H. Spaan & T. Burke, Bedford: EUSPEN , 2012, Vol. 1, p. 158-161Conference paper (Refereed)
    Abstract [en]

    There is an increasing requirement from manufacturing industries for improved technologies to measure surface topography. New instruments have to be accurate; robust to be used on the industry floor; non-invasive; automatic; and sufficiently fast to be used in real time as well as to simultaneously measure over a large area. The industrial applications are plenty:

    • On-line quality control of machined parts,
    • Direct feed back to the manufacturing process,
    • Analysis and selection of surface texture/structure.

    This paper presents new developments in interferometer techniques for new robust area-based topographic instruments.

  • 2.
    Chalangar, Ebrahim
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Linköping University, Norrköping, Sweden.
    Machhadani, Houssaine
    Linköping University, Linköping, Sweden.
    Lim, Seung-Hyuk
    Linköping University, Linköping, Sweden.
    Karlsson, K. Fredrik
    Linköping University, Linköping, Sweden.
    Nur, Omer
    Linköping University, Norrköping, Sweden.
    Willander, Magnus
    Linköping University, Norrköping, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Linköping University, Norrköping, Sweden & Lund University, Lund, Sweden.
    Influence of morphology on electrical and optical properties of graphene/Al-doped ZnO-nanorod composites2018In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 29, no 41, article id 415201Article in journal (Refereed)
    Abstract [en]

    The development of future 3D-printed electronics relies on the access to highly conductive inexpensive materials that are printable at low temperatures (<100 C). The implementation of available materials for these applications are, however, still limited by issues related to cost and printing quality. Here, we report on the simple hydrothermal growth of novel nanocomposites that are well suited for conductive printing applications. The nanocomposites comprise highly Al-doped ZnO nanorods grown on graphene nanoplatelets (GNPs). The ZnO nanorods play the two major roles of (i) preventing GNPs from agglomerating and (ii) promoting electrical conduction paths between the graphene platelets. The effect of two different ZnO-nanorod morphologies with varying Al-doping concentration on the nanocomposite conductivity and the graphenedispersity are investigated. Time-dependent absorption, photoluminescence and photoconductivity measurements show that growth in high pH solutions promotes a better graphene dispersity, higher doping levels and enhanced bonding between the graphene and the ZnO nanorods. Growth in low pH solutions yields samples characterized by a higher conductivity and a reduced number of surface defects. These samples also exhibit a large persistent photoconductivity attributed to an effective charge separation and transfer from the nanorods to the graphene platelets. Our findings can be used to tailor the conductivity of novel printable composites, or for fabrication of large volumes of inexpensive porous conjugated graphene-semiconductor composites. © 2018 IOP Publishing Ltd.

  • 3.
    Flys, Olena
    et al.
    Halmstad University, School of Business, Engineering and Science, Mechanical Engineering and Industrial Design (MTEK). SP Technical Research Institute of Sweden, Borås, Sweden.
    Källberg, S.
    SP Technical Research Institute of Sweden, Borås, Sweden.
    Ged, G.
    LCM LNE-Cnam, Trappes, France.
    Silvestri, Z.
    LCM LNE-Cnam, Trappes, France.
    Rosén, Bengt-Göran
    Halmstad University, School of Business, Engineering and Science, Mechanical Engineering and Industrial Design (MTEK), Functional Surfaces.
    Characterization of surface topography of a newly developed metrological gloss scale2015In: Surface Topography: Metrology and Properties, ISSN 2051-672X, Vol. 3, no 4, article id 045001Article in journal (Refereed)
    Abstract [en]

    In the European Joint Research Project 'Multidimensional Reflectometry for Industry', a new gloss scale was developed with the aim to represent different levels of gloss, hue, roughness, and refractive indices. In this paper, the surfaces of six selected samples were thoroughly investigated using various measuring techniques in order to verify the outcome of the novel manufacturing processes in terms of distinct levels as well as types of surface roughness. The aim of the evaluation was to capture surface structures in different wavelength intervals utilizing a confocal microscope, a coherence scanning interferometer, and an atomic force microscope. Power spectral density functions were also calculated from the measurements and used to determine suitability of techniques for different roughness scales. The measurements show that the expected surface characteristics as well as different RMS roughness values are intimately connected to the perceived glossiness.

  • 4.
    Friel, R. J.
    et al.
    Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Loughborough, Leicestershire, United Kingdom.
    Harris, R. A.
    Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Loughborough, Leicestershire, United Kingdom.
    A nanometre-scale fibre-to-matrix interface characterization of an ultrasonically consolidated metal matrix composite2010In: Proceedings of the Institution of mechanical engineers. Part L, journal of materials, ISSN 1464-4207, E-ISSN 2041-3076, Vol. 224, no 1, p. 31-40Article in journal (Refereed)
    Abstract [en]

    Future 'smart' structures have the potential to revolutionize many engineering applications. One of the possible methods for creating smart structures is through the use of shape memory alloy (SMA) fibres embedded into metal matrices. Ultrasonic consolidation (UC) allows the embedding of SMAs into metal matrices while retaining the SMA's intrinsic recoverable deformation property. In this work, NiTi SMA fibres were successfully embedded into an Al 3003 (0) matrix via the UC layer manufacturing process. Initially the plastic flow of the Al matrix and the degree of fibre encapsulation were observed using optical microscopy. Then microstructural grain and sub-grain size variation of the Al 3003 (0) matrix at the fibre-matrix interface, and the nature of the fibre-matrix bonding mechanism, were studied via the use of focused ion beam (FIB) cross-sectioning, FIB imaging, scanning electron microscopy, and mechanical peel testing. The results show that the inclusion of the NiTi SMA fibres had a significant effect on the surrounding Al matrix microstructure during the UC process. Additionally, the fibre-matrix bonding mechanism appeared to be mechanical entrapment with the SMA surface showing signs of fatigue from the UC embedding process.

  • 5.
    Hussain, Laiq
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS). Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Karimi, Mohammad
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS). Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Berg, Alexander
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Jain, Vishal
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS). Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Borgström, Magnus T.
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Gustafsson, Anders
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Samuelson, Lars
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS). Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Defect-induced infrared electroluminescence from radial GaInP/AlGaInP quantum well nanowire array light- emitting diodes2017In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 28, no 48, article id 485205Article in journal (Refereed)
    Abstract [en]

    Radial GaInP/AlGaInP nanowire array light-emitting diodes (LEDs) are promising candidates for novel high-efficiency solid state lighting due to their potentially large strain-free active emission volumes compared to planar LEDs. Moreover, by proper tuning of the diameter of the nanowires, the fraction of emitted light extracted can be significantly enhanced compared to that of planar LEDs. Reports so far on radial growth of nanowire LED structures, however, still point to significant challenges related to obtaining defect-free radial heterostructures. In this work, we present evidence of optically active growth-induced defects in a fairly broad energy range in vertically processed radial GaInP/AlGaInP quantum well nanowire array LEDs using a variety of complementary experimental techniques. In particular, we demonstrate strong infrared electroluminescence in a spectral range centred around 1 eV (1.2 μm) in addition to the expected red light emission from the quantum well. Spatially resolved cathodoluminescence studies reveal a patchy red light emission with clear spectral features along the NWs, most likely induced by variations in QW thickness, composition and barriers. Dark areas are attributed to infrared emission generated by competing defect-assisted radiative transitions, or to trapping mechanisms involving non-radiative recombination processes. Possible origins of the defects are discussed. © 2017 IOP Publishing Ltd

  • 6.
    Jafari Jam, Reza
    et al.
    Division of Solid State Physics/Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Heurlin, Magnus
    Division of Solid State Physics/Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Kvennefors, Anders
    Division of Solid State Physics/Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Graczyk, Mariusz
    Division of Solid State Physics/Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Jain, Vishal
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Division of Solid State Physics/Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Borgström, Magnus T.
    Division of Solid State Physics/Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Division of Solid State Physics/Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Samuelson, Lars
    Division of Solid State Physics/Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Maximov, Ivan
    Division of Solid State Physics/Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Nanoimprint Lithography and Gold Electroplating for Nanowire Seed Particle Definition2013Conference paper (Refereed)
  • 7.
    Jain, Vishal
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. 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.
    Lindgren, David
    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.
    Hussein, Laiq
    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.
    Capasso, Federico
    School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA.
    Borgström, Magnus T.
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Gustafsson, Anders
    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.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Large area photodetectors based on InP NWs with InAs/InAsP QWs2014Conference paper (Refereed)
    Abstract [en]

    Focal plane arrays have a widespread use in infrared imaging, which often rely on cryogenic cooling to curtail the dark current level necessary for a reasonable signal-to-noise ratio. Quantum well (QW) infrared photodetectors are uniform over large areas, but suffer from a severe drawback related to the selection rules for intersubband absorption. An interesting alternative is self-assembled III-V nanowires offering a key advantage owing to the enhanced absorption by optical resonance effects and strain relaxation.We present electrical and optical results from large ensembles of n+-i-n+ InP NWs, axially grown on InP substrates with InAs/InAsP QWs embedded within the i-segment, designed for both interband and intersubband detection. The NWs are contacted in a vertical geometry using 50 nm SiO2 as the insulating layer and ITO as the top contact. We first investigate the crystal quality of the InAsP QWs grown in 180 nm diameter NWs, using PL, CL and TEM. To achieve more abrupt InAs/InAsP QWs, we grow 130 nm diameter NWs and deplete the In present in the Au catalysts. The effect of n-doping on the device performance is studied by fabricating two different NW geometries, with and without an n+-segment grown before the nominal i-segment in the NW. In addition, the position of the QWs within the i-segment is varied to further scrutinize effects related to doping and crystal structure. Finally, we report spectrally resolved photocurrent results from the QWs in the near-infrared region and discuss about the further developments needed for intersubband detection.

  • 8.
    Jain, Vishal
    et al.
    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.
    Nowzari, Ali
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Lindgren, David
    Solid State Physics and the Nanometer Structure Consortium, Lund University, 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
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Large Area Photodetectors at 1.3/1.55 μm Based on InP/InAsP NWs2014Conference paper (Refereed)
    Abstract [en]

    Optical communication systems benefit a lot from APDs due to their increased photocurrent gain as compared to conventional photodetectors. An avalanche region in a high bandgap material is especially useful to avoid the tunneling leakage currents in smaller bandgap materials needed for absorption at 1.3/1.55 µm wavelengths. Self-assembled III-V semiconductor nanowires have a key advantage owing to the enhanced absorption due to optical resonance effects and the strain relaxation in NWs, thus facilitating monolithic integration of different heterostructures on cheaper substrates. Here, we present electrical and optical results from large ensembles of InP/InAsP NWs, axially grown on p+ InP substrates. The NW base consists of an InP p-n junction acting as the avalanche region followed by an InP/InAsP absorption region, and ending with a top InP n+-segment. The 130nm diameter NW arrays are contacted in a vertical geometry using SiO2 as the insulating layer and ITO as the top contact. The n-doping in the avalanche region is varied to study it’s influence on the avalanche mechanism. Also the bandgap in the absorption region is varied from pure InP to smaller bandgap InAsP by varying the As content. Clear interband signals from different crystal phases of InP/InAsP are observed in photocurrent spectroscopy. Moreover, the photocurrent spectra are consistent with spatially resolved photoluminescence signals. We also report on polarization and angle dependent photocurrent response of the NW array.

  • 9.
    Jain, Vishal
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), 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
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), 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
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    A comparative study of nanowire based infrared p+-i-n+ photodetectors2012Conference paper (Refereed)
    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.

  • 10.
    Karimi, Mohammad
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS). Lund University, Lund, Sweden.
    Heurlin, Magnus
    Lund University, Lund, Sweden.
    Samuelson, Lars
    Lund University, Lund, Sweden.
    Borgström, Magnus. T
    Lund University, Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS). Lund University, Lund, Sweden.
    Infrared Photodetectors Based on Nanowire Arrays – Towards Far Infrared Region2017Conference paper (Refereed)
    Abstract [en]

    Nanowire semiconductors are promising candidates for optoelectronic applications such as solar cells, photodetectors and lasers due to their quasi-1D geometry and large surface to volume ratio. The functional wavelength range of NW-based detectors is typically limited to the visible/near-infrared region. In this work, we present electrical and optical properties of novel IR photodetectors based on large square millimeter ensembles (>1million) of vertically processed semiconductor heterostructure nanowires (NWs) grown on InP substrates which operates in longer wavelengths. InP NWs comprising single or multiple (20) InAs/InAsP QDics axially embedded in an n-i-n geometry, have been grown on InP substrates using MOVPE. The NWs are contacted in vertical direction by ALD deposition of 50 nm SiO2 as an insulating layer followed by sputtering of ITO and evaporation of Ti and Au as top contact layer. In order to extend the sensitivity range to the mid-wavelength and long-wavelength regions, the intersubband transition within conduction band of InAsP QDisc is suggested. We present first experimental indications of intersubband photocurrent in NW geometry and discuss important design parameters for realization of intersubband detectors. Key advantages with the proposed design include large degree of freedom in choice of materials compositions, possible enhanced optical resonance effects due to periodically ordered NW arrays and the compatibility with silicon substrates. We believe that our novel detector design offers the route towards monolithic integration of compact and sensitive III-V NW long wavelength detectors with Si technology.

  • 11.
    Karimi, Mohammad
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS). Lund University, Lund, Sweden.
    Heurlin, Magnus
    Lund University, Lund, Sweden.
    Samuelson, Lars
    Lund University, Lund, Sweden.
    Borgström, Magnus T.
    Lund University, Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS). Lund University, Lund, Sweden.
    Intersubband Photodetectors Realized with InAsP/InP Quantum Discs-in-Nanowire Heterostructures2017Conference paper (Other academic)
  • 12.
    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
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), 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 Diodes2017In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 17, no 6, p. 3599-3606Article in journal (Refereed)
    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

  • 13.
    Mansouri, Ebrahim
    Halmstad University, School of Information Technology.
    Studies on Radiation-induced Defects in InP/InAsP Nanowire-based Quantum Disc-in wire Photodetectors2018Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Photodetectors are used in many applications such as digital and thermal cameras or in solar panels. They can also be designed to detect the omnipresent high-energy radiation/particles, and for radiation imaging in biomedical applications. Novel nanostructures offer significant advantages compared to traditional designs for the realization of fast, sensitive, compact and cheap sensors and efficient solar cells. Examples of such nanostructures include quantum dots (QDs), quantum wells (QWs) and NW arrays. This thesis is devoted to experimental investigations of effects of high-energy (1 MeV) protons on the optical and electrical performance of InP/InAsP NW-based QDiscs-in wire photodetectors. The proton-induced degradation of the optical performance has been studied by means of Fourier Transform Infrared (FTIR) photocurrent spectroscopy. The spectrally resolved photocurrent (PC) and current-voltage (I-V) characteristics were measured at low temperature (5 K and 77K) and at room temperature (300K) before and after 1 MeV proton irradiation under vacuum conditions with fluences ranging from 1.0×1012–3.0×1013 cm-2. The particle radiation exposure has been done in the Ion Beam Accelerator at the Department of Nuclear Physics Department at Lund University. Considering both PC and I-V characteristics, it was found that the devices were sensitive to all proton irradiation at all fluences. In general, the PC intensity significantly increased after radiation for all fluences, however, a week after exposure the PC and dark current gradually recovered. At 3×1012 p/cm2 fluence level, it was figured out that photocurrent which attributed to QDiscs disappeared for a couple of days after exposure, however, over time and gradually, those started to manifest again even at low and room temperatures, causing radiation-induced changes in device parameters to be time-dependent; however, it was not recorded any signals related to QDiscs at fluence of 3×1013 p/cm2. Substantial changes in the dark I-V characteristics, as well as increases in the dark current, are observed after irradiation. The influence of proton irradiation on light and dark current characteristics also indicated that NW structures are a good potential candidate for radiation harsh-environment applications. It was also observed a significant increase in dark current after the radiation for all devices, however, by applying the voltage to the photodetectors, the PC and I-V characteristics gradually being to diminish, which may be attributed to an annealing process.

  • 14.
    Ngo, Tuan Nghia
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE).
    Zubritskaya, Irina
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE).
    Electrical and Optical Characterization of InP Nanowire Ensemble Photodetectors2012Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Photodetectors are semiconductor devices that can convert optical signals into electrical signals. There is a wide range of photodetector applications such as fiber optics communication, infrared heat camera sensors, as well as in equipment used for medical and military purposes.

    Nanowires are thin needle-shaped structures made of semiconductor materials, e.g. gallium arsenide (GaAs), indium phosphide (InP) or silicon (Si). Their small size, well-controlled crystal structure and composition as well as the possibility to fabricate them monolithically on silicon make them ideally suited for sensitive photodetectors with low noise.

    In this project, Fourier Transform Infrared (FTIR) Spectroscopy is used to investigate the optical characteristics of InP nanowire-based PIN photodetectors. The corresponding electrical characteristics are also measured using very sensitive instrumentation. A total of 4 samples consisting of processed nanowires with 80 nm diameter but different density and length have been examined. The experiments were conducted from 78K (-196oC) to room temperature 300K (27oC). The spectrally resolved photocurrent and current-voltage (IV) curves (in darkness & under illumination) for different temperatures have been studied and analyzed.

    The samples show excellent IV performance with very low leakage currents. The photocurrent scales with the number of nanowires, from which we conclude that most photocurrent is generated in the substrate. Spectrally resolved photocurrent data, recorded at different temperatures, display strong absorption in the near-infrared region with interesting peaks that reveal the underlying optical processes in the substrate and nanowires, respectively. The nature of the absorption peaks is discussed in detail.

    This study is an important step towards integration of optically efficient III-V nanoscale devices on cheap silicon substrates for applications e.g. on-chip optical communication and solar cells for energy harvesting.

  • 15.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Nanoscale devices for future optoelectronics2012Conference paper (Refereed)
  • 16.
    Saj, Damian
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE).
    Saj, Izabela
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE).
    Nanowire-based InP solar cell materials2012Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this project, a new type of InP solar cell was investigated. The main idea is that light is converted to electrical current in p-i-n photodiodes formed in thin InP semiconductor nanowires epitaxially grown on an InP substrate. Two different types of samples were investigated. In the first sample type (series C03), the substrate was used as a common p-type electrode, whereas a short p-segment was included in all nanowires for the second sample type (B07).

    Current – voltage (I-V) characteristics with and without illumination were measured, as well as spectrally resolved photocurrents with and without bias. The main conclusion is that the p-i-n devices showed good rectifying behavior with an onset in photocurrent that agrees with the corresponding energy band gap of InP. An interesting observation was that in series B07 (with included p-segments) the photocurrent was determined by the band gap of hexagonal Wurtzite crystal structure, whereas series C03 (without p-segments) displayed a photocurrent dominated by the InP substrate which has a Zincblende crystal structure. We found that the overall short-circuit current was ten as large for the latter sample, stressing the importance of the substrate as a source of photocurrent.

1 - 16 of 16
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf