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  • 1.
    Berg, Alexander
    et al.
    Lund University, Lund, Sweden.
    Yazdi, Sadegh
    Technical University of Denmark, Lyngby, Denmark.
    Nowzari, Ali
    Lund University, Lund, Sweden.
    Storm, Kristian
    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). Lund University, Lund, Sweden.
    Vainorius, Neimantas
    Lund University, Lund, Sweden.
    Samuelson, Lars
    Lund University, Lund, Sweden.
    Wagner, Jakob B.
    Technical University of Denmark, Lyngby, Denmark.
    Borgström, Magnus T.
    Lund University, Lund, Sweden.
    Radial Nanowire Light-Emitting Diodes in the (AlxGa1-x)yIn1-yP Material System2016Ingår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 16, nr 1, s. 656-662Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nanowires have the potential to play an important role for next-generation light-emitting diodes. In this work, we present a growth scheme for radial nanowire quantum-well structures in the AlGaInP material system using a GaInP nanowire core as a template for radial growth with GaInP as the active layer for emission and AlGaInP as charge carrier barriers. The different layers were analyzed by X-ray diffraction to ensure lattice-matched radial structures. Furthermore, we evaluated the material composition and heterojunction interface sharpness by scanning transmission electron microscopy energy dispersive X-ray spectroscopy. The electro-optical properties were investigated by injection luminescence measurements. The presented results can be a valuable track toward radial nanowire light-emitting diodes in the AlGaInP material system in the red/orange/yellow color spectrum. © 2015 American Chemical Society.

  • 2.
    Borschel, Christian
    et al.
    Institute for Solid State Physics, Jena University, Max-Wien-Platz 1, 07743 Jena, Germany.
    Messing, Maria
    Avd. f. Fasta tillståndets fysik, Lunds Universitet.
    Borgström, Magnus T.
    Avd. f. Fasta tillståndets fysik, Lunds Universitet.
    Paschoal, Waldomiro
    Avd. f. Fasta tillståndets fysik, Lunds Universitet / Tillämpad matematik och fysik (MPE-lab), MPE-lab.
    Wallentin, Jesper
    Avd. f. Fasta tillståndets fysik, Lunds Universitet.
    Kumar, Sandeep
    Avd. f. Fasta tillståndets fysik, Lunds Universitet.
    Mergenthaler, Kilian
    Avd. f. Fasta tillståndets fysik, Lunds Universitet.
    Deppert, Knut
    Avd. f. Fasta tillståndets fysik, Lunds Universitet.
    Canali, C. M.
    Högskolan i Kalmar.
    Pettersson, Håkan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Samuelson, Lars
    Avd. f. Fasta tillståndets fysik, Lunds Universitet.
    Ronning, Carsten
    Institute for Solid State Physics, Jena University, Max-Wien-Platz 1, 07743 Jena, Germany.
    A New Route toward Semiconductor Nanospintronics: Highly Mn-Doped GaAs Nanowires Realized by Ion-Implantation under Dynamic Annealing Conditions2011Ingår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 11, nr 9, s. 3935-3940Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on highly Mn-doped GaAs nanowires (NWs) of high crystalline quality fabricated by ion beam implantation, a technique that allows doping concentrations beyond the equilibrium solubility limit. We studied two approaches for the preparation of Mn-doped GaAs NWs: First, ion implantation at room temperature with subsequent annealing resulted in polycrystalline NWs and phase segregation of MnAs and GaAs. The second approach was ion implantation at elevated temperatures. In this case, the single-crystallinity of the GaAs NWs was maintained, and crystalline, highly Mn-doped GaAs NWs were obtained. The electrical resistance of such NWs dropped with increasing temperature (activation energy about 70 meV). Corresponding magnetoresistance measurements showed a decrease at low temperatures, indicating paramagnetism. Our findings suggest possibilities for future applications where dense arrays of GaMnAs nanowires may be used as a new kind of magnetic material system.

  • 3.
    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.
    Jain, Vishal
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS). 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.
    Maximov, Ivan
    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
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (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.
    III-V nanowire synthesis by use of electrodeposited gold particles2015Ingår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 15, nr 1, s. 134-138Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Semiconductor nanowires are great candidates for building novel electronic devices. Considering the cost of fabricating such devices, substrate reuse and gold consumption are the main concerns. Here we report on implementation of high throughput gold electrodeposition for selective deposition of metal seed particles in arrays defined by lithography for nanowire synthesis. By use of this method, a reduction in gold consumption by a factor of at least 300 was achieved, as compared to conventional thermal evaporation for the same pattern. Because this method also facilitates substrate reuse, a significantly reduced cost of the final device is expected. We investigate the morphology, crystallography, and optical properties of InP and GaAs nanowires grown from electrodeposited gold seed particles and compare them with the properties of nanowires grown from seed particles defined by thermal evaporation of gold. We find that nanowire synthesis, as well as the material properties of the grown nanowires are comparable and quite independent of the gold deposition technique. On the basis of these results, electrodeposition is proposed as a key technology for large-scale fabrication of nanowire-based devices.

  • 4.
    Jurgilaitis, A.
    et al.
    Department of Physics & MAX IV Laboratory, Lund University, Lund, Sweden.
    Enquist, H.
    MAX IV Laboratory, Lund University, Lund, Sweden.
    Andreasson, Björn Pererik
    Department of Physics, Lund University, Lund, Sweden.
    Persson, A. I. H.
    Department of Physics, Lund University, Lund, Sweden.
    Borg, B. M.
    Department of Electrical and Information Technology, Lund University, Lund, Sweden.
    Caroff, P.
    Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra, Australia.
    Dick, K. A.
    Department of Physics, Lund University, Lund, Sweden & Division of Polymer and Materials Chemistry, Department of Chemistry, Lund University, Lund, Sweden.
    Harb, M.
    Department of Physics & MAX IV Laboratory, Lund University, Lund, Sweden.
    Linke, H.
    Department of Physics, Lund University, Lund, Sweden.
    Nüske, R.
    Department of Physics, Lund University, Lund, Sweden.
    Wernersson, L.-E.
    Department of Electrical and Information Technology, Lund University, Lund, Sweden.
    Larsson, J.
    Department of Physics, Lund University, Lund, Sweden.
    Time-Resolved X-ray Diffraction Investigation of the Modified Phonon Dispersion in InSb Nanowires2014Ingår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 14, nr 2, s. 541-546Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The modified phonon dispersion is of importance for understanding the origin of the reduced heat conductivity in nanowires. We have measured the phonon dispersion for 50 nm diameter InSb (111) nanowires using time-resolved X-ray diffraction. By comparing the sound speed of the bulk (3880 m/s) and that of a classical thin rod (3600 m/s) to our measurement (2880 m/s), we conclude that the origin of the reduced sound speed and thereby to the reduced heat conductivity is that the C44 elastic constant is reduced by 35% compared to the bulk material. © 2014 American Chemical Society.

  • 5.
    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 Infrared2018Ingår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 18, nr 1, s. 365-372Artikel i tidskrift (Refereegranskat)
    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.

  • 6.
    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 Photodetectors2017Ingår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 17, nr 6, s. 3356-3362Artikel i tidskrift (Refereegranskat)
    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.

  • 7.
    Karimi, Mohammad
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS). Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Zeng, Xulu
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Witzigmann, Bernd
    Computational Electronics and Photonics Group and CINSaT, University of Kassel, Kassel, Germany.
    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.
    High Responsivity of InP/InAsP Nanowire Array Broadband Photodetectors Enhanced by Optical Gating2019Ingår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High-performance photodetectors operating in the near-infrared (0.75−1.4 μm) and short-wave infrared (1.4−3.0 μm) portion ofthe electromagnetic spectrum are key components in many optical systems.Here, we report on a combined experimental and theoretical study of squaremillimeter array infrared photodetectors comprising 3 million n+−i−n+ In Pnanowires grown by MOVPE from periodically ordered Au seed particles. Thenominal i-segment, comprising 20 InAs0.40P0.60 quantum discs, was grown byuse of an optimized Zn doping to compensate the nonintentional n-doping.The photodetectors exhibit bias- and power-dependent responsivities reachingrecord-high values of 250 A/W at 980 nm/20 nW and 990 A/W at 532 nm/60nW, both at 3.5 V bias. Moreover, due to the embedded quantum discs, thephotoresponse covers a broad spectral range from about 0.70 to 2.5 eV, ineffect outperforming conventional single InGaAs detectors and dual Si/Gedetectors. The high responsivity, and related gain, results from a novel proposed photogating mechanism, induced by the complex charge carrier dynamics involving optical excitation and recombination in the quantum discs and interface traps, which reduces the electron transport barrier between the highly doped ncontact and the i-segment. The experimental results obtained are in perfect agreement with the proposed theoretical model and represent a significant step forward toward understanding gain in nanoscale photodetectors and realization of commercially viable broadband photon detectors with ultrahigh gain. © 2019 American Chemical Society.

  • 8.
    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 Diodes2017Ingår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 17, nr 6, s. 3599-3606Artikel i tidskrift (Refereegranskat)
    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

  • 9.
    Kumar, Sandeep
    et al.
    Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Paschoal, Waldomiro
    Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Johannes, Andreas
    Institute for Solid State Physics, Jena University, Jena, Germany.
    Jacobsson, Daniel
    Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Borschel, Christian
    Institute for Solid State Physics, Jena University, Jena, Germany.
    Pertsova, Anna
    Linneaus University, Kalmar, Sweden.
    Wang, Chih-Han
    Institute of Physics, Academia Sinica, Taipei, Taiwan.
    Wu, Maw-Kuen
    Institute of Physics, Academia Sinica, Taipei, Taiwan.
    Canali, C. M.
    Linneaus University, Kalmar, Sweden.
    Ronning, Carsten
    Institute for Solid State Physics, Jena University, Jena, Germany.
    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). Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Magnetic Polarons and Large Negative Magnetoresistance in GaAs Nanowires implanted with Mn Ions2013Ingår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 13, nr 11, s. 5079-5084Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on low-temperature magnetotransport and SQUID measurements on heavily doped Mn-implanted GaAs nanowires. SQUID data recorded at low magnetic fields exhibit clear signs of the onset of a spin-glass phase with a transition temperature of about 16 K. Magnetotransport experiments reveal a corresponding peak in resistance at 16 K and a large negative magnetoresistance, reaching 40% at 1.6 K and 8 T. The negative magnetoresistance decreases at elevated temperatures and vanishes at about 100 K. We interpret our transport data in terms of spin-dependent hopping in a complex magnetic nanowire landscape of magnetic polarons, separated by intermediate regions of Mn impurity spins, forming a paramagnetic/spin-glass phase. Copyright © 2013 American Chemical Society

  • 10.
    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 (CAMP).
    Michalak, L.
    Kalmar University.
    Canali, C. M.
    Kalmar University.
    Samuelson, L.
    Lund University.
    Pettersson, Håkan
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (CAMP).
    Tunneling anisotropic magnetoresistance in Co/AlOx/Au tunnel junctions2008Ingår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 8, nr 3, s. 848-852Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We observe spin-valve-like effects in nanoscaled 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.

  • 11.
    Liu, Ruisheng
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
    Pettersson, Håkan
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
    Michalak, L.
    Department of Chemistry and Biomedical Sciences, Kalmar University.
    Canali, C.M.
    Department of Chemistry and Biomedical Sciences, Kalmar University.
    Samuelson, L.
    Solid State Physics/ the Nanometer Structure Consortium, Lund University.
    Probing spin accumulation in Ni/Au/Ni single-electron transistors with efficient spin injection and detection electrodes2007Ingår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 7, nr 1, s. 81-85Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have investigated spin accumulation in Ni/Au/Ni single-electron transistors assembled by atomic force microscopy. The fabrication technique is unique in that unconventional hybrid devices can be realized with unprecedented control, including real-time tunable tunnel resistances. A grid of Au disks, 30 nm in diameter and 30 nm thick, is prepared on a SiO2 surface by conventional e-beam writing. Subsequently, 30 nm thick ferromagnetic Ni source, drain, and side-gate electrodes are formed in similar process steps. The width and length of the source and drain electrodes were different to exhibit different coercive switching fields. Tunnel barriers of NiO are realized by sequential Ar and O2 plasma treatment. By use of an atomic force microscope with specially designed software, a single nonmagnetic Au nanodisk is positioned into the 25 nm gap between the source and drain electrodes. The resistance of the device is monitored in real time while the Au disk is manipulated step-by-step with angstrom-level precision. Transport measurements in magnetic field at 1.7 K reveal no clear spin accumulation in the device, which can be attributed to fast spin relaxation in the Au disk. From numerical simulations using the rate-equation approach of orthodox Coulomb blockade theory, we can put an upper bound of a few nanoseconds on the spin-relaxation time for electrons in the Au disk. To confirm the magnetic switching characteristics and spin injection efficiency of the Ni electrodes, we fabricated a test structure consisting of a Ni/NiO/Ni magnetic tunnel junction with asymmetric dimensions of the electrodes similar to those of the single-electron transistors. Magnetoresistance measurements on the test device exhibited clear signs of magnetic reversal and a maximum tunneling magnetoresistance of 10%, from which we deduced a spin polarization of about 22% in the Ni electrodes. © 2007 American Chemical Society.

  • 12.
    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 Devices2015Ingår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 15, nr 3, s. 1809-1814Artikel i tidskrift (Refereegranskat)
    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.

  • 13.
    Paschoal Jr., Waldomiro
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
    Kumar, Sandeep
    Solid State Physics/The Nanometer Structure Consortium, Lund University, Box 118, SE-221 00 Lund, Sweden.
    Borschel, Christian
    Institute for Solid State Physics, Jena University, Max-Wien-Platz 1, 07743 Jena, Germany.
    Wu, Phillip
    Solid State Physics/The Nanometer Structure Consortium, Lund University, Box 118, SE-221 00 Lund, Sweden.
    Canali, Carlo M.
    Division of Physics, School of Computer Science, Physics and Mathematics, Linneaus University, 39233 Kalmar, Sweden.
    Ronning, Carsten
    Institute for Solid State Physics, Jena University, Max-Wien-Platz 1, 07743 Jena, Germany.
    Samuelson, Lars
    Solid State Physics/The Nanometer Structure Consortium, Lund University, Box 118, SE-221 00 Lund, Sweden.
    Pettersson, Håkan
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
    Hopping Conduction in Mn Ion-Implanted GaAs Nanowires2012Ingår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 12, nr 9, s. 4838-4842Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on temperature-dependent charge transport in heavily doped Mn+ implanted GaAs nanowires.The results clearly demonstrate that the transport is governedby temperature-dependent hopping processes, with a crossoverbetween nearest neighbor hopping and Mott variable rangehopping at about 180 K. From detailed analysis, we haveextracted characteristic hopping energies and correspondinghopping lengths. At low temperatures, a strongly nonlinearconductivity is observed which reflects a modified hoppingprocess driven by the high electric field at large bias.

  • 14.
    Pettersson, Håkan
    et al.
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
    Trägårdh, Johanna
    Solid State Physics and the Nanometer Consortium, Lund University, Lund, SUEDE.
    Persson, Ann I.
    Solid State Physics and the Nanometer Consortium, Lund University, Lund, SUEDE.
    Landin, Lars
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
    Hessman, Dan
    Solid State Physics and the Nanometer Consortium, Lund University, Lund, SUEDE.
    Samuelson, Lars E.
    Solid State Physics and the Nanometer Consortium, Lund University, Lund, SUEDE.
    Infrared Photodetectors in Heterostructure Nanowires2006Ingår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 6, nr 2, s. 229-232Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on spectrally resolved photocurrent measurements on single self-assembled nanowire heterostructures. The wires, typically 3 μm long with an average diameter of 85 nm, consist of InAs with a 1 μm central part of InAsP. Two different sets of wires were prepared with phosphorus contents of 15 ±3% and 35 ±3%, respectively, as determined by energy-dispersive spectroscopy measurements made in transmission electron microscopy. Ohmic contacts are fabricated to the InAs ends of the wire using e-beam lithography. The conduction band offset between the InAs and InAsP regions virtually removes the dark current through the wires at low temperature. In the optical experiments, interband excitation in the phosphorus-rich part of the wires results in a photocurrent with threshold energies of about 0.65 and 0.82 eV, respectively, in qualitative agreement with the expected band gap of the two compositions. Furthermore, a strong polarization dependence is observed with an order of magnitude larger photocurrent for light polarized parallel to the wire than for light polarized perpendicular to the wire. We believe that these wires form promising candidates as nanoscale infrared polarization-sensitive photodetectors.

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