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  • 51.
    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

  • 52.
    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
    Halmstad University, School of Information Technology, 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 Ions2013In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 13, no 11, p. 5079-5084Article in journal (Refereed)
    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

  • 53.
    Liu, Ruisheng
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Applied Mathematics and Physics (CAMP).
    Michalak, L.
    Kalmar University.
    Canali, C. M.
    Kalmar University.
    Samuelson, L.
    Lund University.
    Pettersson, Håkan
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Applied Mathematics and Physics (CAMP).
    Tunneling anisotropic magnetoresistance in Co/AlOx/Au tunnel junctions2008In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 8, no 3, p. 848-852Article in journal (Refereed)
    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.

  • 54.
    Liu, Ruisheng
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), 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
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Tunneling Anisotropic Magnetoresistance in Co/AlOx /Au Tunnel Junctions2008Conference paper (Refereed)
    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.

  • 55.
    Liu, Ruisheng
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Applied Mathematics and Physics (CAMP).
    Pettersson, Håkan
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Applied Mathematics and Physics (CAMP).
    Michalak, L.
    Kalmar University.
    Canali, C. M.
    Kalmar University.
    Suyatin, D.
    Lund University.
    Samuelson, L.
    Lund University.
    Large magnetoresistance in Co/Ni/Co ferromagnetic single electron transistors2007In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 90, no 12, p. 123111-Article in journal (Refereed)
    Abstract [en]

    The authors report on magnetotransport investigations of nanoscaled ferromagnetic Co/Ni/Co single electron transistors. As a result of reduced size, the devices exhibit single electron transistor characteristics at 4.2 K. Magnetotransport measurements carried out at 1.8 K reveal tunneling magnetoresistance (TMR) traces with negative coercive fields, which the authors interpret in terms of a switching mechanism driven by the shape anisotropy of the central wirelike Ni island. A large TMR of about 18% is observed within a finite source-drain bias regime. The TMR decreases rapidly with increasing bias, which the authors tentatively attribute to excitation of magnons in the central island.

  • 56.
    Liu, Ruisheng
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
    Pettersson, Håkan
    Halmstad University, School of Information Science, Computer and Electrical Engineering (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 electrodes2007In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 7, no 1, p. 81-85Article in journal (Refereed)
    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.

  • 57.
    Liu, Ruisheng
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), 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 microscopy2006Conference paper (Refereed)
    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.

  • 58.
    Liu, Ruisheng
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Pettersson, Håkan
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), 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 Transistors2007In: 2007 7th IEEE International Conference on Nanotechnology - IEEE-NANO 2007, Proceedings, Piscataway, N.J.: IEEE Press, 2007, p. 420-421Conference paper (Other academic)
    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.

  • 59.
    Liu, Ruisheng S.
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Applied Mathematics and Physics (CAMP).
    Canali, C. M.
    Kalmar University, Kalmar, Sweden.
    Samuelson, L.
    Lund University, Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Applied Mathematics and Physics (CAMP).
    Magnetoresistance studies on CoAl OX Au and CoAl OX NiAu tunnel structures2008In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 93, no 20, p. 203107-203107-3Article in journal (Refereed)
    Abstract [en]

    We report on magnetoresistance (MR) studies on CoAl OX Au and CoAl OX NiAu magnetic tunnel junctions. In spite of the fact that the difference between the two samples is merely a 3 nm thick Ni layer, there is a sharp contrast in MR behavior indicating that the electronic structure at the interface between the ferromagnetic electrodes and the insulating barrier dominates the MR signal. The former sample exhibits a clear tunneling anisotropic MR (TAMR), with the characteristic correlation between resistance and current direction, in contrast to the latter sample which displays a conventional tunneling MR (TMR) dominated by the relative orientation between the magnetization directions of the two electrodes. In addition, the TAMR has a much stronger temperature dependence than the TMR, indicating a much faster drop-off of the tunneling density of states anisotropy than the tunneling electron spin polarization with increasing temperature. Finally, we propose a possible simple way to distinguish TAMR from normal TMR by measuring the resistance of the device at different angles of the external magnetic field. 2008 American Institute of Physics.

  • 60.
    Liu, Ruisheng
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Applied Mathematics and Physics (CAMP).
    Suyatin, D.
    Lund University.
    Pettersson, Håkan
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Applied Mathematics and Physics (CAMP).
    Samuelson, L.
    Lund University.
    Assembling ferromagnetic single-electron transistors by atomic force microscopy2007In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 18, no 5, p. 055302-Article in journal (Refereed)
    Abstract [en]

    We demonstrate the assembly of nanoscale ferromagnetic single-electron transistors using atomic force microscopy for imaging as well as for nanoscale manipulation. A single 30 nm Au disc, forming the central island of the transistor, is manipulated with angstrom precision into the gap between a plasma-oxidized Ni source and drain electrodes. The tunnel resistances can be tuned in real time during the device fabrication by repositioning the Au disc. Transport measurements reveal long-term stable single-electron transistor characteristics at 4.2 K. The well-controlled devices with very small central islands facilitate future in-depth studies of the interplay between Coulomb blockade, spin-dependent tunnelling and spin accumulation in ferromagnetic single-electron transistors at elevated temperatures.

  • 61.
    Nilsson, Pernilla
    et al.
    Halmstad University, School of Education, Humanities and Social Science, Research on Education and Learning within the Department of Teacher Education (FULL).
    Pendrill, A-M
    Göteborgs Universitet.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS).
    Learning physics with the body: 10-åringars erfarenheter och upplevelser av Newtons mekanik i åkattraktionerna på Liseberg2004Conference paper (Refereed)
  • 62.
    Nilsson, Pernilla
    et al.
    Halmstad University, School of Education, Humanities and Social Science, Research on Education and Learning within the Department of Teacher Education (FULL).
    Pendrill, Anne-Marie
    Physics and Engineering Physics, Gothenburg University.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS).
    Learning physics with the body2004Conference paper (Refereed)
    Abstract [en]

    Experiments can be one way to interest pupils in science. Here, we describe experiments that incorporate children’s experiences of the body in a setting outside the classroom and shared with teacher students. Pre- and post-tests show that children recalled a number of significant observations concerning the concepts of gravity and inertia. In interviews after the event, the children had a chance to reflect on their experiences. Their responses are analysed and categorised with a socio-cultural approach of learning.

  • 63.
    Nilsson, Pernilla
    et al.
    Halmstad University, School of Education, Humanities and Social Science, Research on Education and Learning within the Department of Teacher Education (FULL).
    Pendrill, Ann-Marie
    Institutionen för fysik, Göteborgs Universitet.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    En jämförande studie av olika elevgruppers förståelse av accelerationsbegreppet2005Conference paper (Refereed)
    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.

  • 64.
    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
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), 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
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), 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 Devices2015In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 15, no 3, p. 1809-1814Article in journal (Refereed)
    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.

  • 65.
    Park, Min-Su
    et al.
    Center for Optoelectronic Convergence Systems, KIST (Korean Institute of Science and Technology), Seoul, Republic of Korea.
    Jain, Vishal
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), 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
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), 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 K2014In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 50, no 23, p. 1731-1733Article in journal (Refereed)
    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

  • 66.
    Paschoal Jr., Waldomiro
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), Applied Mathematics and Physics (CAMP). Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Kumar, Sandeep
    Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Borschel, Christian
    Institute for Solid State Physics, Jena University, Jena, Germany.
    Borgström, Magnus
    Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Ronning, Carsten
    Institute for Solid State Physics, Jena University, Jena, Germany.
    Canali, Carlo
    Division of Physics, School of Computer Science, Physics and Mathematics, Linneaus University, Kalmar, Sweden.
    Samuelson, Lars
    Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), Applied Mathematics and Physics (CAMP). Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Electron transport in Mn+ implanted GaAs nanowires2012Conference paper (Refereed)
    Abstract [en]

    Mn-doped GaAs semiconductors have generated great interest in current research regarding the evolution from a paramagnetic insulator to a ferromagnetic metal governed by a carrier mediated exchange interaction. The interplay between the charge carriers in a semiconductor and the electron spin of incorporated ferromagnetic metals can be utilized for novel spin-sensitive spintronic devices. We have fabricated highly Mn-doped, single-crystalline GaAs nanowires (NWs) by ion implantation at elevated temperatures to facilitate in-situ dynamic annealing. To exploit these nanowires in spintronic applications, a detailed understanding of fundamental charge transport mechanisms is however necessary. It is generally expected that new features, different from any bulk counterparts, will emerge in systems with reduced dimensionality e.g. quasi-1D NWs. Here we report on a detailed study of different charge transport mechanisms and localization-related effects in single Mn-doped GaAs NWs in the temperature range from 300K to 1.6K, and with magnetic fields ranging from 0T to 8T. In general, the resistance of the nanowires increases strongly from a few M* at 300K to several G* at 1.6 K. More specially, the temperature dependence displays several different interesting regimes described by distinctly different models. Furthermore, the current-voltage (I-V) characteristics becomes strongly non-linear as the temperature decreases and shows apparent power-law behavior at low temperatures. In particular, we interpret our transport data in the temperature range from 80K to 275K in terms of a variable range hopping process influenced by Mn-induced disorder in the NWs. Below 50K the magnetotransport data reveals a large negative magnetoresistance (MR) under both paralleland perpendicular magnetic fields. We are presently developing models to explain this large MR signal, including low-temperature transport mechanisms and possible magnetic interaction between Mn ions.

  • 67.
    Paschoal Jr., Waldomiro
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (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
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
    Hopping Conduction in Mn Ion-Implanted GaAs Nanowires2012In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 12, no 9, p. 4838-4842Article in journal (Refereed)
    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.

  • 68.
    Paschoal Jr., Waldomiro
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Kumar, Sandeep
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), 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
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), 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
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Magnetoresistance in Mn ion-implanted GaAs:Zn nanowires2014In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 104, no 15, article id 153112Article in journal (Refereed)
    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.

  • 69.
    Pettersson, Håkan
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Nanometer Structure Consortium, Lund University.
    Nanoscale devices for future opto-and magnetoelectronics2008Conference paper (Refereed)
  • 70.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Nanoscale devices for future optoelectronics2012Conference paper (Refereed)
  • 71.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Nanowire Infrared Photodetectors2016Conference paper (Refereed)
    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.

  • 72.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Nanowire-based Infrared Photodetectors2015Conference paper (Refereed)
    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.

  • 73.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Nanowire-based infrared photodetectors2014Conference paper (Refereed)
    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.

  • 74.
    Pettersson, Håkan
    Lund University, Lund, Sweden.
    Physics and Technology of Nanowire Infrared Photodetectors2016In: EMN Photodetectors Meeting, 2016Conference paper (Refereed)
    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.

  • 75.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Lund University, Lund, Sweden.
    Physics and Technology of Nanowire Photodetectors2017In: 2017 Technical Summaries: OPTP, 2017, p. 279-279Conference paper (Refereed)
    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.

  • 76.
    Pettersson, Håkan
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), 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 manipulation2007In: Bulletin of the American Physical Society, ISSN 0003-0503, Vol. 52, no 1Article in journal (Refereed)
    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. 

  • 77.
    Pettersson, Håkan
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS).
    Bååth, Lars B.
    Halmstad University, School of Business, Engineering and Science, Mechanical Engineering and Industrial Design (MTEK), Fotonik och mikrovågsteknik.
    Carlsson, N.
    Division of Solid State Physics, Lund University, Sweden.
    Seifert, W.
    Division of Solid State Physics, Lund University, Sweden.
    Samuelson, L.
    Division of Solid State Physics, Lund University, Sweden.
    Case study of an InAs quantum dot memory: Optical storing and deletion of charge2001In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 79, no 1, p. 78-80Article in journal (Refereed)
    Abstract [en]

    We have studied self-assembled InAs quantum dots embedded in an InP matrix using photocapacitance and photocurrent spectroscopy. These dots are potentially promising for memories due to the large confinement energy for holes. In this work we have realized simple quantum dot memory by placing the dots in the space–charge region of a Schottky junction. Our measurements reveal that a maximum of about one hole can be stored per dot. We also find that illumination for an extended period deletes the stored charge. We show that these limitations do not reflect the intrinsic properties of the dots, but rather the sample structure in combination with deep traps present in the sample.

  • 78.
    Pettersson, Håkan
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
    Bååth, Lars B.
    Halmstad University, School of Business and Engineering (SET), Mechanical Engineering and Industrial Design (MTEK).
    Carlsson, Niclas
    Division of Solid State Physics, Lund University, Lund, Sweden.
    Seifert, Werner
    Division of Solid State Physics, Lund University, Lund, Sweden.
    Samuelson, Lars
    Division of Solid State Physics, Lund University, Lund, Sweden.
    Optically induced charge storage and current generation in InAs quantum dots2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 65, no 7, p. 0733041-0733044Article in journal (Refereed)
    Abstract [en]

    We report on optically induced charge storage effects and current generation in self-assembled InAs quantum dots embedded in an InP matrix. Illumination with photons of energy higher than about 0.86 eV efficiently loads the dots with a maximum of about 1 hole/dot. The spectral response at lower photon energy is strongly enhanced at elevated temperatures. We present a detailed balance model for the dots and discuss the thermally assisted optical excitation processes pertinent to hole accumulation. We also show that these processes make the dots act as nanometer-scaled temperature-dependent current generators.

  • 79.
    Pettersson, Håkan
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Conache, Gabriela
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), 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 manipulation2008Conference paper (Refereed)
    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.

  • 80.
    Pettersson, Håkan
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), 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 bias2010In: Bulletin of the American Physical Society: APS March Meeting 2010, Volume 55, Number 2, American Physical Society , 2010Conference paper (Refereed)
    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.

  • 81.
    Pettersson, Håkan
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), 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 Properties2010In: Bulletin of American Physical Society: APS March Meeting 2010, Volume 55, Number 2, American Physical Society , 2010Conference paper (Refereed)
    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.

  • 82.
    Pettersson, Håkan
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
    Landin, Lars
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
    Fu, Ying
    Department of Microtechnology and Nanoscience, Chalmers University of Technology, Göteborg, Sweden.
    Kleverman, Mats
    Division of Solid State Physics, Lund University, Lund, Sweden.
    Borgström, Magnus
    Division of Solid State Physics, Lund University, Lund, Sweden.
    Seifert, Werner
    Division of Solid State Physics, Lund University, Lund, Sweden.
    Samuelson, Lars
    Division of Solid State Physics, Lund University, Lund, Sweden.
    Photocurrent spectroscopy on self-assembled InAs quantum dots embedded in InP2005In: Microelectronics Journal, ISSN 0026-2692, Vol. 36, no 3-6, p. 227-230Article in journal (Refereed)
    Abstract [en]

    In this work, we report on an overview of recent results from Fourier transform photocurrent (FTPC) measurements in the infrared spectral region on ensembles of self-assembled InAs quantum dots embedded in a matrix of InP. In interband PC, clear signals related to the dots are observed. Comparing the PC- and PL spectra, we observe that the fundamental transition is absent in the PC spectra, which we interpret in terms of Pauliblocking due to a filled electron ground state of the dots. Our results furthermore suggest that an Auger process is involved in forming the interband PC signal. In intersubband PC, peaks related to transitions from the dots' ground- and first excited states to the conduction band of the matrix are observed. Using a novel approach of combining FTPC with illumination from an additional external non-modulated light source, we have measured the spectral distribution of photoionization of excitons in quantum dots and found an exciton binding energy in good agreement with theoretical calculations.

  • 83.
    Pettersson, Håkan
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
    Landin, Lars
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
    Kleverman, Mats
    Division of Solid State Physics, Lund University, Lund, Sweden.
    Seifert, Werner
    Division of Solid State Physics, Lund University, Lund, Sweden.
    Samuelson, Lars
    Division of Solid State Physics, Lund University, Lund, Sweden.
    Fu, Ying
    Phys. Electron. and Photonics, Department of Physics, Gothenburg University, Gothenburg, Sweden.
    Willander, Magnus
    Phys. Electron. and Photonics, Department of Physics, Gothenburg University, Gothenburg, Sweden.
    Intersubband photoconductivity of self-assembled InAs quantum dots embedded in InP2004In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 95, no 4, p. 1829-1831Article in journal (Refereed)
    Abstract [en]

    The results from photoconductivity (PC) measurements on InAs dots embedded in InP are presented. The PC technique is recently applied to the study of InAs dots embedded in matrices of GaAs and Al0.3Ga0.7As matrix, respectively. It is demonstrated that this technique reveals important new physical insight into the electronic structure of the InAs/InP dots, information that cannot easily be obtained by other techniques.

  • 84.
    Pettersson, Håkan
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
    Landin, Lars
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
    Liu, R. S.
    Division of Solid State Physics, Lund University, Lund, Sweden.
    Seifert, Werner
    Division of Solid State Physics, Lund University, Lund, Sweden.
    Pistol, Mats Erik
    Division of Solid State Physics, Lund University, Lund, Sweden.
    Samuelson, Lars
    Division of Solid State Physics, Lund University, Lund, Sweden.
    Photoexcitation of excitons in self-assembled quantum dots2004In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 85, no 21, p. 5046-5048Article in journal (Refereed)
    Abstract [en]

    Using an approach of combining Fourier transform infrared spectroscopy with resonant illumination from a secondary external light source, we have measured the photocurrent (PC) for multiple layers of self-assembled InAs dots embedded in a matrix of InP. Without external illumination, we observe photoexcitation of electrons from bound states in the dots to the InP barrier. By additional illumination from the external light source, a strong broadening of the PC signal is observed. We interpret this broadening in terms of photoexcitation of electrons in the presence of additional holes in the dots created by the external light source. We extract the spectral distribution of the photoexcitation process at 6 and 77 K, respectively, and show by comparison with theoretical calculations that it is consistent with an exciton binding energy of 20 meV.

  • 85.
    Pettersson, Håkan
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Liu, Ruisheng S.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), 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 microscopy2008In: Nanostructures in electronics and photonics / [ed] Rahman, Faiz, Singapore: Pan Stanford Publishing, 2008, p. 29-40Chapter in book (Refereed)
  • 86.
    Pettersson, Håkan
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS). Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Liu, Ruisheng S.
    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.
    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 microscopy2008In: Nanostructures in Electronics and Photonics / [ed] Faiz Rahman, London: Pan Stanford Publishing, 2008, p. 29-40Chapter in book (Other academic)
    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.

  • 87.
    Pettersson, Håkan
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), 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 technique2010In: Bulletin of American Physical Society: APS March Meeting 2010, Volume 55, Number 2, American Physical Society , 2010Conference paper (Refereed)
    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.

  • 88.
    Pettersson, Håkan
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (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
    Halmstad University, School of Information Science, Computer and Electrical Engineering (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 Nanowires2006In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 6, no 2, p. 229-232Article in journal (Refereed)
    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.

  • 89.
    Pettersson, Håkan
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Zubritskaya, Irina
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Nghia, Ngo Tuan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Wallentin, Jesper
    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.
    Storm, Kristian
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Landin, Lars
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Wickert, Peter
    Sol Voltaics AB, Ideon Science Park, 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.
    Electrical and optical properties of InP nanowire ensemble p(+)-i-n(+) photodetectors2012In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 23, no 13, article id 135201Article in journal (Refereed)
    Abstract [en]

    We report on a comprehensive study of electrical and optical properties of efficient near-infrared p(+)-i-n(+) photodetectors based on large ensembles of self-assembled, vertically aligned i-n(+) InP nanowires monolithically grown on a common p(+) InP substrate without any buffer layer. The nanowires have a polytype modulated crystal structure of wurtzite and zinc blende. The electrical data display excellent rectifying behavior with an ideality factor of about 2.5 at 300 K. The ideality factor scales with 1/T, which possibly reflects deviations from classical transport models due to the mixed crystal phase of the nanowires. The observed dark leakage current is of the order of merely similar to 100 fA/nanowire at 1 V reverse bias. The detectors display a linear increase of the photocurrent with reverse bias up to about 10 pA/nanowire at 5 V. From spectrally resolved measurements, we conclude that the photocurrent is primarily generated by funneling photogenerated carriers from the substrate into the NWs. Contributions from direct excitation of the NWs become increasingly important at low temperatures. The photocurrent decreases with temperature with an activation energy of about 50 meV, which we discuss in terms of a temperature-dependent diffusion length in the substrate and perturbed transport through the mixed-phase nanowires. © 2012 IOP Publishing Ltd.

  • 90.
    Rögnvaldsson, Thorsteinn
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS).
    Brink, Joachim
    Halmstad University.
    Florén, Henrik
    Halmstad University, School of Business, Engineering and Science, Centre for Innovation, Entrepreneurship and Learning Research (CIEL).
    Gaspes, Veronica
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS).
    Holmgren, Noél
    University of Skövde, Skövde, Sweden.
    Lutz, Mareike
    Halmstad University.
    Nilsson, Pernilla
    Halmstad University, School of Education, Humanities and Social Science, Research on Education and Learning within the Department of Teacher Education (FULL).
    Olsfelt, Jonas
    Halmstad University.
    Svensson, Bertil
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS).
    Ericsson, Claes
    Halmstad University, School of Education, Humanities and Social Science, Research on Education and Learning within the Department of Teacher Education (FULL).
    Gustafsson, Linnea
    Halmstad University, School of Education, Humanities and Social Science, Contexts and Cultural Boundaries (KK).
    Hoveskog, Maya
    Halmstad University, School of Business, Engineering and Science, Centre for Innovation, Entrepreneurship and Learning Research (CIEL).
    Hylander, Jonny
    Halmstad University, School of Business, Engineering and Science, Biological and Environmental Systems (BLESS).
    Jonsson, Magnus
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS).
    Nygren, Jens
    Halmstad University, School of Health and Welfare, Centre of Research on Welfare, Health and Sport (CVHI).
    Rosén, Bengt-Göran
    Halmstad University, School of Business, Engineering and Science, Mechanical Engineering and Industrial Design (MTEK).
    Sandberg, Mikael
    Halmstad University, School of Education, Humanities and Social Science, Center for Social Analysis (CESAM).
    Benner, Mats
    Lund University, Lund, Sweden.
    Berg, Martin
    Halmstad University, School of Education, Humanities and Social Science, Center for Social Analysis (CESAM).
    Bergvall, Patrik
    Halmstad University.
    Carlborg, Anna
    Halmstad University.
    Fleischer, Siegfried
    Halmstad University, School of Business, Engineering and Science, Biological and Environmental Systems (BLESS).
    Hållander, Magnus
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS).
    Mattsson, Marie
    Halmstad University, School of Business, Engineering and Science, Biological and Environmental Systems (BLESS).
    Olsson, Charlotte
    Halmstad University, School of Business, Engineering and Science, Biological and Environmental Systems (BLESS).
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS).
    Rundquist, Jonas
    Halmstad University, School of Business, Engineering and Science, Centre for Innovation, Entrepreneurship and Learning Research (CIEL).
    Sahlén, Göran
    Halmstad University, School of Business, Engineering and Science, Biological and Environmental Systems (BLESS).
    Waara, Sylvia
    Halmstad University, School of Business, Engineering and Science, Biological and Environmental Systems (BLESS).
    Weisner, Stefan
    Halmstad University, School of Business, Engineering and Science, Biological and Environmental Systems (BLESS).
    Werner, Sven
    Halmstad University, School of Business, Engineering and Science, Biological and Environmental Systems (BLESS).
    ARC13 – Assessment of Research and Coproduction: Reports from the assessment of all research at Halmstad University 20132014Report (Other (popular science, discussion, etc.))
    Abstract [en]

    During 2013, an evaluation of all the research conducted at Halmstad University was carried out. The purpose was to assess the quality of the research, coproduction, and collaboration in research, as well as the impact of the research. The evaluation was dubbed the Assessment of Research and Coproduction 2013, or ARC13. (Extract from Executive Summary)

  • 91.
    Shang, Xianjung
    et al.
    State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, China.
    Yu, Ying
    State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, China.
    Li, Mifeng
    State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, China.
    Wang, Lijuan
    State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, China.
    Zha, Guowei
    State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, China.
    Ni, Haiqiao
    State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, China.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Fu, Ying
    Science for Life Laboratory, Department of Applied Physics, Royal Institute of Technology, Stockholm, Sweden.
    Niu, Zhichuan
    State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, China.
    Effect of tunable dot charging on photoresponse spectra of GaAs p-i-n diode with InAs quantum dots2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 118, no 24, p. 244503-1-244503-9, article id 244503Article in journal (Refereed)
    Abstract [en]

    Quantum dots (QDs)-embedded photodiodes have demonstrated great potential on detectors. A modulation of QD charging opens intriguing possibilities for adaptive sensing with bias-tunable detector characteristics. Here, we report on a p-i-n GaAs photodiode with InAs QDs whose charging is tunable due to unintentional Be diffusion and trap-assisted tunneling of holes, from bias- and temperature (T)-dependent photocurrent spectroscopy. For the sub-bandgap spectra, the T-dependent relative intensities "QD-s/WL" and "WL/GaAs" (WL: wetting layer) reflect a dominant tunneling under -0.9 V (trap-assisted tunneling from the top QDs) and a dominant thermal escape under -0.2 ~ 0.5 V (from the bottom QDs since the top ones are charged and inactive for optical absorption) from QD s-state, a dominant tunneling from WL and an enhanced QD charging at > 190 K (related to trap level ionization). For the above-bandgap spectra, the degradation of the spectral profile (especially that near GaAs bandedge) as the bias and T tune (especially under -0.2 ~ 0.2 V and at > 190 K) can be well explained by the enhanced photoelectron capture in QDs with tunable charging; the dominant spectral profile with no degradation under 0.5 V is due to a saturated electron capture in charged QDs (i.e. charging neutralization). QD level simulation and schematic bandstructures help to understand these effects. © 2015 AIP Publishing LLC

  • 92.
    Shang, X.-J.
    et al.
    Chinese Academy of Sciences.
    He, J.-F.
    Chinese Academy of Sciences.
    Li, M.-F.
    Chinese Academy of Sciences.
    Zhan, F.
    Chinese Academy of Sciences.
    Ni, H.-Q.
    Chinese Academy of Sciences.
    Niu, Z.-C.
    Chinese Academy of Sciences.
    Pettersson, Håkan
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Fu, Ying
    Division of Theoretical Chemistry and Biology, School of Biotechnology, Royal Institute of Technology, Stockholm, Sweden.
    Quantum-dot-induced optical transition enhancement in InAs quantum-dot-embedded p-i-n GaAs solar cells2011In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 99, no 11, p. 113514-113514-3Article in journal (Refereed)
    Abstract [en]

    Photocurrents (PCs) of three p–i–n GaAs solar cells, sample A with InAs quantum dots (QDs) embedded in the depletion region, B with QDs in the n region, and C without QDs, were studied experimentally and theoretically. Above GaAs bandgap, the PC of A is increased, while B is decreased with respect to C, since in A, the QD-induced reflection of hole wave function increases its overlap with electron wave function so that the optical transition rate is enhanced, while carrier mobility in B is reduced due to QD-induced potential variations. Moreover, A and B have increased PCs in the sub-GaAs-bandgap range due to QD optical absorptions.

  • 93.
    Stepanova, K. V.
    et al.
    Petrozavodsk State University, Petrozavodsk, Russia.
    Yakovleva, N. M.
    Petrozavodsk State University, Petrozavodsk, Russia.
    Kokatev, Alexander N.
    Petrozavodsk State University, Petrozavodsk, Russia.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Influence of annealing on the structure of nanoporous oxide films on the surface of titanium‒aluminum powder alloy2016In: Journal of Surface Investigation. X-ray, Synchrotron and Neutron Techniques, ISSN 1027-4510, Vol. 10, no 5, p. 933-941Article in journal (Refereed)
    Abstract [en]

    Oxide films obtained during anodization of Ti‒40% Al sintered powder samples in fluorine-containing electrolytes are investigated. With scanning electron microscopy and X-ray phase analysis, it is demonstrated that an X-ray amorphous nanoporous anodic oxide film is formed on the surface of the powder microparticles under optimal anodization conditions. After annealing at T = 1093 K in air and vacuum (10‒2 Pa), the oxide films are revealed to crystallize with its regular porous structure retained. The composition of the polycrystalline anodic-oxide films annealed in air is a mixture involving TiO2 (anatase and rutile) and α- and γ-Al2O3 phases and Ti2O3 and Al2TiO5 traces. The vacuum annealing process makes it possible to identify TiO2, in which anatase is the main phase, α- and γ-Al2O3, and Ti2O3 and TiO traces. However, rutile is not revealed. The presented results indicate that the application of the anodic nanostructuring of Ti‒40% Al powders is promising for the obtainment of new photocatalytic active nanomaterials. © 2016, Pleiades Publishing, Ltd.

  • 94.
    Suyatin, Dmitry
    et al.
    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.
    Nebol’sin, Valery A.
    Voronezh State Technical University, Voronezh, Russian Federation.
    Trägårdh, Johanna
    Division of Solid State Physics, Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Messing, Maria
    Division of Solid State Physics, Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Wagner, Jakob B.
    Division of Polymer and Materials Chemistry, Lund University, Lund, Sweden.
    Persson, Olof
    Division of Synchrotron Radiation Research, Lund University, Lund, Sweden.
    Timm, Rainer
    Division of Synchrotron Radiation Research, Lund University, Lund, Sweden.
    Mikkelsen, Anders
    Division of Synchrotron Radiation Research, Lund University, Lund, Sweden.
    Maximov, Ivan
    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.
    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.
    Strong Schottky barrier reduction at Au-catalyst/GaAs-nanowire interfaces by electric dipole formation and Fermi-level unpinning2014In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 5, article id 3221Article in journal (Refereed)
    Abstract [en]

    Nanoscale contacts between metals and semiconductors are critical for further downscaling of electronic and optoelectronic devices. However, realizing nanocontacts poses significant challenges since conventional approaches to achieve ohmic contacts through Schottky barrier suppression are often inadequate. Here we report the realization and characterization of low n-type Schottky barriers (∼0.35 eV) formed at epitaxial contacts between Au-In alloy catalytic particles and GaAs-nanowires. In comparison to previous studies, our detailed characterization, employing selective electrical contacts defined by high-precision electron beam lithography, reveals the barrier to occur directly and solely at the abrupt interface between the catalyst and nanowire. We attribute this lowest-to-date-reported Schottky barrier to a reduced density of pinning states (∼10 17 m-2) and the formation of an electric dipole layer at the epitaxial contacts. The insight into the physical mechanisms behind the observed low-energy Schottky barrier may guide future efforts to engineer abrupt nanoscale electrical contacts with tailored electrical properties. © 2014 Macmillan Publishers Limited.

  • 95.
    Suyatin, Dmitry
    et al.
    Avd. f. Fasta Tillståndets Fysik, Lunds Universitet.
    Trägårdh, Johanna
    Avd. f. Fasta Tillståndets Fysik, Lunds Universitet.
    Messing, Maria
    Avd. f. Fasta Tillståndets Fysik, Lunds Universitet.
    Wagner, Jakob
    Avd. f. Materialkemi, Lunds Universitet.
    Montelius, Lars
    Avd. f. Fasta Tillståndets Fysik, Lunds Universitet.
    Pettersson, Håkan
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Samuelson, Lars
    Avd. f. Fasta Tillståndets Fysik, Lunds Universitet.
    Nano-Schottky contacts realized by bottom-up technique2010In: INEC 2010 - 2010 3rd International Nanoelectronics Conference, Proceedings / [ed] Chu, PKI, Piscataway, N.J.: IEEE Press, 2010, p. 252-253Conference paper (Refereed)
    Abstract [en]

    Properties of nanostructures realized by bottom-up techniques are often different from their bulk counterparts. Here we present a study of a nano-Schottky contact formed at the interface between a gold catalytic particle and an epitaxially grown GaxIn1-xAs/InAs nanowire. Selective electrical connections formed to the catalytic particle on one side and to the InAs segment on the other side allowed electrical and optical characterization of the formed junction. We demonstrate that the heterostructure region adjacent to the catalytic particle may act as an ultra-small volume unipolar photodetector with potentially ultra-fast response.

  • 96.
    Trägårdh, Johanna
    et al.
    Solid State Physics, Lund University, Lund, Sweden.
    Persson, Ann
    Solid State Physics, Lund University, Lund, Sweden.
    Hessman, Dan
    Solid State Physics, Lund University, Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Landin, Lars
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Samuelson, Lars
    Solid State Physics, Lund University, Lund, Sweden.
    Photocurrent Spectroscopy on Single Heterostructure Nanowires2005In: Symposium EE: Progress in Semiconductor Materials V-Novel Materials and Electronic and Optoelectronic Applications, 2005, p. 753-753Conference paper (Refereed)
  • 97.
    Vincent, J.K.
    et al.
    Physical Electron. Photonics Group, University of Göteborg, Chalmers University of Technology, S-412 96 Göteborg, Sweden.
    Narayan, V.
    Physical Electron. Photonics Group, University of Göteborg, Chalmers University of Technology, S-412 96 Göteborg, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS).
    Willander, M.
    Physical Electron. Photonics Group, University of Göteborg, Chalmers University of Technology, S-412 96 Göteborg, Sweden.
    Jeppson, K.
    Solid State Electronics Group, Department of Microelectronics, Chalmers University of Technology, S-412 96 Göteborg, Sweden.
    Bengtsson, L.
    Department of Computer Engineering, Sch. of Electrical and Comp. Eng., Chalmers University of Technology, S-412 96 Göteborg, Sweden.
    Theory of a room-temperature silicon quantum dot device as a sensitive electrometer2004In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 95, no 1, p. 323-326Article in journal (Refereed)
    Abstract [en]

    We consider theoretically the use of a room-temperature silicon quantum dot based device for electrometer applications. The low power device includes two split gates that quantize the electronic energy levels in the emitter and collector regions. The base consists of a silicon quantum dot buried in silicon dioxide. The small size of the dotand quantization of the states in the leads combined to allow the device to operate at room temperature. The nonlinear current-voltage characteristics can be significantly altered by small changes to the potential of the split gates. Power dissipation in the device therefore changes with the split gate voltage, and this can be exploited in electrometerapplications. A simple model of the power dissipated when the device is part of a microwave resonant inductor-resistor-capacitor tank circuit suggests that large changes indevice power can be achieved by changing the gate voltage, thereby forming a measurable signal. We also demonstrate that the power dissipation in the device changes as the base width is varied, and that the current through the device increases exponentially with a decrease in base width. (©2004 American Institute of Physics)

  • 98.
    Wang, Qin
    et al.
    Acreo ICT AB, Kista, Sweden.
    Jafari, Mehrdad
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Hussein, Laiq
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Song, Jindong
    Center for Optoelectronic Convergence Systems, KIST (Korean Institute of Science and Technology), Seoul, South Korea.
    Choi, Won Jun
    Center for Optoelectronic Convergence Systems, KIST (Korean Institute of Science and Technology), Seoul, South Korea.
    Han, Il Ki
    Center for Optoelectronic Convergence Systems, KIST (Korean Institute of Science and Technology), Seoul, South Korea.
    Lee, Eun Hye
    Center for Optoelectronic Convergence Systems, KIST (Korean Institute of Science and Technology), Seoul, South Korea.
    Park, Suk In
    Center for Optoelectronic Convergence Systems, KIST (Korean Institute of Science and Technology), Seoul, South Korea.
    Lim, Ju Young
    Laser-IT Center, Korea Photonics Technology Institute, Seoul, South Korea.
    Karim, Amir
    Acreo ICT AB, Kista, Sweden.
    Andersson, Jan Y.
    Acreo ICT AB, Kista, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    MWIR interband transitions in type-II (III) In(GaAl)Sb quantum dots2015Conference paper (Refereed)
    Abstract [en]

    In this work we present an alternative approach for realizing desired IR devices with appropriate operating wavelengths in the MWIR region utilizing In(GaAl)Sb quantum dots embedded in an InAs matrix grown by MBE. The QDs exhibit spatially indirect interband transitions in a type-II broken bandgap alignment, with a transition energy that can be tuned by bandgap and strain engineering utilizing either the quantum dot size or the incorporation of Ga or (GaAl) into the QDs. Furthermore, the growth of such QDs does not require sophisticated epitaxial designs needed for superlattices or quantum cascade structures regarding large numbers of alternating layers and very exact interfaces. The QD structures are expected to exhibit key advantages for IR devices e.g. higher operating temperature, lower power consumption, size, weight, and cost. The structural and composition properties of designed and grown In(GaAl)Sb QDs were characterized using AFM, SEM, TEM, and XRD. The corresponding optical properties, both in terms of absorption and emission, were analyzed and compared for selected QD samples before and after annealing at 650 °C.

  • 99.
    Willander, Magnus
    et al.
    Linköping University, Linköping, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Preface2017In: International Journal of High Speed Electronics and Systems, ISSN 0129-1564, Vol. 26, no 1-2, article id 1702001Article in journal (Refereed)
  • 100.
    Willander, Magnus
    et al.
    Linköping University, Linköping, Sweden.
    Pettersson, HåkanHalmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Special Issue on Scaling and Integration of High Speed Electronics and Optomechanical Systems2017Conference proceedings (editor) (Refereed)
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