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  • 1.
    Aghaeipour, Mahtab
    Lund University, Lund, Sweden.
    Tailoring the Optical Response of III-V Nanowire Arrays2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Semiconductor nanowires show a great deal of promise for applications in a wide range of important fields, including photovoltaics, biomedicine, and information technology. Developing these exciting applications is strongly dependent on understanding the fundamental properties of nanowires, such as their optical resonances and absorption spectra. In this thesis we explore optical absorption spectra of arrays of vertical III-V nanowires with a special emphasis on structures optimized to enhance absorption in the solar spectrum. First, we analyze experimentally determined absorption spectra of both indium phosphide (InP) and gallium phosphide (GaP) nanowire arrays. The study provides an intuitive understanding of how the observed absorption resonances in the nanowires may be tuned as a function of their geometrical parameters and crystal structure. As a consequence, the spectral position of absorption resonances can be precisely controlled through the nanowire diameter. However, the results highlight how the blue-shift in the optical absorption resonances as the diameter of the nanowires decreases comes to a halt at low diameters. The stop point is related to the behavior of the refractive indices of the nanowires. The wavelength of the stop is different for nanowire polytypes of similar dimensions due to differences in their refractive indices. We then present a theoretical argument that it is important to consider symmetry properties when tailoring the optical modes excited in the nanowires for enhanced absorption. We show that absorption spectra may be enhanced compared to vertical nanowires at normal incidence by tilting the nanowires with normal incidence light, or by using off-normal incidence with vertical nanowires. This is because additional optical modes inside the nanowires are excited when the symmetry is broken. Looking forward to omnidirectional applications, we consider branched nanowires as a way to enhance the absorption spectra at normal incidence by taking advantage of simultaneous excitation of the spectrally different optical modes in the branches and the stems. Third, we describe in theoretical terms how integrating distributed Bragg reflectors (DBRs) with the nanowires can improve absorption spectra compared to conventional nanowires. DBRs provide a way to employ light trapping mechanisms which increases the optical path length of the excited modes and thereby improves the absorption of the excited modes. At normal incidence, DBR-nanowires improve the absorption efficiency to 78%, compared to 72% for conventional nanowires. We show that the efficiency is increased to 85% for an off-normal incident angle of 50˚. Overall, our results show that studies of optical resonances in nanowires that take the light-matter interaction into account provide opportunities to develop novel optical and optoelectronic functionalities in nanoscience and nanotechnology.

  • 2.
    Aghaeipour, Mahtab
    et al.
    Lund University, Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Lund University, Lund, Sweden.
    Enhanced broadband absorption in nanowire arrays with integrated Bragg reflectors2018In: Nanophotonics, E-ISSN 2192-8614, Vol. 7, no 5, p. 819-825Article in journal (Refereed)
    Abstract [en]

    A near-unity unselective absorption spectrum is desirable for high-performance photovoltaics. Nanowire arrays are promising candidates for efficient solar cells due to nanophotonic absorption resonances in the solar spectrum. The absorption spectra, however, display undesired dips between the resonance peaks. To achieve improved unselective broadband absorption, we propose to enclose distributed Bragg reflectors (DBRs) in the bottom and top parts of indium phosphide (InP) nanowires, respectively. We theoretically show that by enclosing only two periods of In0.56Ga0.44As/InPDBRs, an unselective 78% absorption efficiency (72% for nanowires without DBRs)is obtained at normal incidence in the spectral range from 300 nm to 920 nm. Under oblique light incidence, the absorption efficiency is enhanced up to about 85% at an incidence angle of 50º. By increasing the number of DBR periods from two to five, the absorption efficiency is further enhanced up to 95% at normal incidence. In this work we calculated optical spectra for InP nanowires, but the results are expected to be valid for other direct band gap III-V semiconductor materials. We believe that our proposed idea of integrating DBRs in nanowires offers great potential for high-performance photovoltaic applications. ©2018 Håkan Pettersson et al., published by De Gruyter, Berlin/Boston.

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  • 3.
    Aghaeipour, Mahtab
    et al.
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS).
    Enhanced optical absorption in nanowires over a desire range of wavelengths2017In: MOC2017 : technical digest of the Twenty-Second Microoptics Conference: November 19-22, 2017, Institute of Industrial Science, The University of Tokyo, Japan, IEEE, 2017, Vol. 2017-November, p. 360-361Conference paper (Refereed)
    Abstract [en]

    Engineering optical absorption in nanowires, over a desire range of wavelengths is of importance to design high-performance nanowire-based photovoltaics. To this end, we integrate the nanowires with distributed Bragg reflectors to enhance absorption spectra of the nanowires and relate the consequent enhancement to increasing the optical path lengths of the modes. © 2017 The Japan Society of Applied Physics.

  • 4.
    Aghaeipour, Mahtab
    et al.
    Lund University, Lund, Sweden.
    Pistol, Mats-Erik
    Lund University, Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS). Lund University, Lund, Sweden.
    Comparative study of absorption efficiency of inclined and vertical InP nanowires2017In: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices VI / [ed] A. Freundlich, L. Lombez, M. Sugiyama, Bellingham, WA: SPIE - International Society for Optical Engineering, 2017, Vol. 10099, article id UNSP 100990SConference paper (Refereed)
    Abstract [en]

    Geometrically designed III-V nanowire arrays are promising candidates for optoelectronics due to their possibility to excite nanophotonic resonances in absorption spectra. Strong absorption resonances can be obtained by proper tailoring of nanowire diameter, length and pitch. Such enhancement of the light absorption is, however, accompanied by undesired resonance dips at specific wavelengths. In this work, we theoretically show that tilting of the nanowires mitigates the absorption dips by exciting strong Mie resonances. In particular, we derive a theoretical optimum inclination angle of about 30 degrees at which the inclined nanowires gain 8% in absorption efficiency compared to vertically standing nanowires in a spectral region matching the intensity distribution of the sun. The enhancement is due to engineering the excited modes inside the nanowires regarding the symmetry properties of the nanowire/light system without increasing the absorbing material. We expect our results to be important for nanowire-based photovoltaic applications. © 2017 SPIE.

  • 5.
    Aghaeipour, Mahtab
    et al.
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Pistol, Mats-Erik
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS). Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Considering Symmetry Properties of InP Nanowire/Light Incidence Systems to Gain Broadband Absorption2017In: IEEE Photonics Journal, E-ISSN 1943-0655, Vol. 9, no 3, article id 4501310Article in journal (Refereed)
    Abstract [en]

    Geometrically designed III-V nanowire arrays are promising candidates for disruptive optoelectronics due to the possibility of obtaining a strongly enhanced absorption resulting from nanophotonic resonance effects. With normally incident light on such vertical nanowire arrays, the absorption spectra exhibit peaks that originate from excitation of HE1m waveguide modes in the constituent nanowires. However, the absorption spectra typically show dips between the absorption peaks. Conventionally, such weak absorption has been counteracted by either making the nanowires longer or by decreasing the pitch of the array, both alternatives effectively increasing the volume of absorbing material in the array. Here, we first study two approaches for compensating the absorption dips by exciting additional Mie resonances: 1) oblique light incidence on vertical InP nanowire arrays and 2) normal light incidence on inclined InP nanowire arrays. We then show that branched nanowires offer a novel route to achieve broadband absorption by taking advantage of simultaneous excitations of Mie resonances in the branches and guided HE1m modes in the stem. Finite element method calculations show that the absorption efficiency is enhanced from 0.72 for vertical nanowires to 0.78 for branched nanowires under normal light incidence. Our work provides new insight for the development of novel efficient photovoltaics with high efficiency and reduced active material volume.

  • 6.
    Ahmed, Rizwan
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE).
    Abbas, Shahid
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE).
    Electrical and Optical Characteristics of InP Nanowires based p-i-n Photodetectors2010Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Photodetectors are a kind of semiconductor devices that convert incoming light to an electrical signal. Photodetectors are classified based on their different structure, fabrication technology, applications and different sensitivity. Infrared photodetectors are widely used in many applications such as night vision, thermal cameras, remote temperature sensing, and medical diagnosis etc.

     

    All detectors have material inside that is sensitive to incoming light. It will absorb the photons and, if the incoming photons have enough energy, electrons will be excited to higher energy levels and if these electrons are free to move, under the effect of an external electric field, a photocurrent is generated.

     

    In this project Fourier Transform Infrared (FT-IR) Spectroscopy is used to investigate a new kind of photodiodes that are based on self-assembled semiconductor nanowires (NWs) which are grown directly on the substrate without any epi-layer. The spectrally resolved photocurrent (at different applied biases) and IV curves (in darkness and illumination) for different temperatures have been studied respectively. Polarization effects (at low and high Temperatures) have been investigated.  The experiments are conducted for different samples with high concentration of NWs as well as with lower concentration of NWs in the temperature range from 78 K (-195ºC) to 300 (27ºC). These photodiodes are designed to work in near infrared (NIR) spectral range.

     

    The results show that the NW photodetectors indeed are promising devices with fairly high break down voltage, change of photocurrent spectra with polarized light, low and constant reverse saturation current (Is). The impact of different polarized light on photocurrent spectra has been investigated and an attempt has been made to clarify the observed double peak of InP photocurrent spectrum. Our investigations also include a comparison to a conventional planar InP p-i-n photodetector.

     

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  • 7.
    Andreasson, Björn Pererik
    et al.
    Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland.
    Janousch, M.
    Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland.
    Staub, U.
    Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland.
    Meijer, G. I.
    IBM Research, Zurich Research Laboratory, Rüschlikon, Switzerland.
    Spatial distribution of oxygen vacancies in Cr-doped SrTiO3 during an electric-field-driven insulator-to-metal transition2009In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 94, no 1, p. Article number: 013513-Article in journal (Refereed)
    Abstract [en]

    Spatially resolved x-ray fluorescence maps are presented that show the introduction and the evolution of oxygen vacancies in chromium-doped strontium titanate during an electric-field-driven insulator-to-metal transition. The vacancies are introduced at the anode and diffuse through the crystal toward the cathode. The spatial distribution of vacancies is explained by a model describing the electrical breakdown as a percolation process. Strong differences in the vacancy distribution were found when the transition took place in air and in a hydrogen-enriched atmosphere. In air, the vacancies disappeared from the surface, whereas in the reducing hydrogen atmosphere, they remained at the surface. © 2009 American Institute of Physics.

  • 8.
    Andreasson, Björn Pererik
    et al.
    Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland.
    Janousch, M.
    Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland.
    Staub, U.
    Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland.
    Meijer, G. I.
    IBM Research, Zurich Research Laboratory, Rüschlikon, Switzerland.
    Delley, B.
    Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland.
    Resistive switching in Cr-doped SrTiO3: An X-ray absorption spectroscopy study2007In: Materials Science & Engineering: B. Solid-state Materials for Advanced Technology, ISSN 0921-5107, E-ISSN 1873-4944, Vol. 144, no 1-3, p. 60-63Article in journal (Refereed)
    Abstract [en]

    X-ray absorption spectroscopy was used to study the microscopic origin of conductance and resistive switching in chromium-doped strontium titanate (Cr:SrTiO3). Differences in the X-ray absorption near edge spectroscopy (XANES) at the Cr K-edge indicate that the valence of Cr changes from 3+ to 4+ underneath the anode of our sample device after the application of an electric field. Spatially resolved X-ray fluorescence microscopy (μ-XRF) maps show that the Cr4+ region retracts from the anode-Cr:SrTiO3 interface after a conducting state has been achieved. This interface region is studied with extended X-ray absorption fine structure (EXAFS) and the results are compared with structural parameters obtained from density functional theory (DFT) calculations. They confirm that oxygen vacancies which are localized at the octahedron with a Cr at its center are introduced at the interface. It is proposed that the switching state is not due to a valence change of chromium but caused by changes of oxygen vacancies at the interface. © 2007 Elsevier B.V. All rights reserved.

  • 9.
    Andreasson, Björn Pererik
    et al.
    Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland.
    Janousch, M.
    Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland.
    Staub, U.
    Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland.
    Meijer, G. I.
    IBM Research, Zurich Research Laboratory, Rüschlikon, Switzerland.
    Ramar, A.
    École Polytechnique Fédérale de Lausanne (EPFL), Centre de Recherche en Physique des Plasmas, Association Euratom-Confédération Suisse, Villigen, Switzerland & Center for Electron Nanoscopy, Technical University of Denmark, Lyngby, Denmark.
    Krbanjevic, J.
    École Polytechnique Fédérale de Lausanne (EPFL), Centre de Recherche en Physique des Plasmas, Association Euratom-Confédération Suisse, Villigen, Switzerland.
    Schaeublin, R.
    École Polytechnique Fédérale de Lausanne (EPFL), Centre de Recherche en Physique des Plasmas, Association Euratom-Confédération Suisse, Villigen, Switzerland.
    Origin of oxygen vacancies in resistive switching memory devices2009In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 190, p. Article number: 012074-Article in journal (Refereed)
    Abstract [en]

    The resistive switching state in Cr-doped SrTiO3 was induced by applying an electric field. This was done in ambient air and in an atmosphere of H2/Ar. The distribution of the thereby introduced oxygen vacancies was studied by spatially resolved X-ray fluorescence images. It was concluded that the oxygen vacancies were introduced in the interface between the SrTiO3 and the positively biased electrode. © 2009 IOP Publishing Ltd.

  • 10.
    Andreasson, Björn Pererik
    et al.
    Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland.
    Janousch, M.
    Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland.
    Staub, U.
    Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland.
    Todorova, T.
    Condensed Matter Theory Group, Paul Scherrer Institut, Villigen, Switzerland.
    Delley, B.
    Condensed Matter Theory Group, Paul Scherrer Institut, Villigen, Switzerland.
    Meijer, G. I.
    IBM Research, Zurich Research Laboratory, Rüschlikon, Switzerland.
    Pomjakushina, E.
    Laboratory for Developments and Methods, Paul Scherrer Institut, Villigen, Switzerland.
    Detecting oxygen vacancies in SrTiO3 by 3d transition-metal tracer ions2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, no 21, p. Article number: 212103-Article in journal (Refereed)
    Abstract [en]

    X-ray absorption experiments on 3d transition-metal tracer ions in SrTiO3 are presented. The absorption spectra of the tracer-ion changed upon reduction in the SrTiO3. This change is due to an oxygen vacancy created at the tracer-ion site. This finding is supported by density-functional theory calculations, which prove that the oxygen vacancies preferentially are created at the tracer-ion sites. Using the chemical sensitivity of x-ray absorption spectroscopy, tracer ions can be used to detect oxygen vacancies in SrTiO3 and possibly in other oxide systems. © 2009 The American Physical Society.

  • 11.
    Anokhina, Ksenia
    et al.
    Avd. f. Fasta Tillståndets Fysik, Lunds Universitet, Lund, Sweden.
    Graczyk, Mariousz
    Avd. f. Fasta Tillståndets Fysik, Lunds Universitet, Lund, Sweden.
    Kvennefors, Anders
    Avd. f. Fasta Tillståndets Fysik, Lunds Universitet, Lund, Sweden.
    Montelius, Lars
    Avd. f. Fasta Tillståndets Fysik, Lunds Universitet, Lund, Sweden.
    Maximov, Ivan
    Avd. f. Fasta Tillståndets Fysik, Lunds Universitet, Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Metal-assisted chemical etching of Si for fabrication of nanoimprint stamps2011Conference paper (Refereed)
  • 12.
    Berg, Alexander
    et al.
    Lund University, Lund, Sweden.
    Yazdi, Sadegh
    Technical University of Denmark, Lyngby, Denmark.
    Nowzari, Ali
    Lund University, Lund, Sweden.
    Storm, Kristian
    Lund University, Lund, Sweden.
    Jain, Vishal
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Lund University, Lund, Sweden.
    Vainorius, Neimantas
    Lund University, Lund, Sweden.
    Samuelson, Lars
    Lund University, Lund, Sweden.
    Wagner, Jakob B.
    Technical University of Denmark, Lyngby, Denmark.
    Borgström, Magnus T.
    Lund University, Lund, Sweden.
    Radial Nanowire Light-Emitting Diodes in the (AlxGa1-x)yIn1-yP Material System2016In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 16, no 1, p. 656-662Article in journal (Refereed)
    Abstract [en]

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

  • 13.
    Bordag, Michael
    et al.
    Leipzig University, Institute for Theoretical Physics, Leipzig, Germany.
    Jede, Ralf
    Raith GmbH, Dortmund, Germany.
    Montelius, Lars
    Lunds University, Physics Department, Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Riu, Jordi
    University Rovira i Vergili, Taragona, Spain.
    Schmucker, Ulrich
    University Rovira i Vergili, Taragona, Spain.
    Zubtsov, Michael
    Fraunhofer Institute for Factory Automation, Magdeburg, Germany.
    Parallel nano-assembly directed by short-range field forces2006In: Proceedings of the 1st IEEE International Conference on Nano/Micro Engineered and Molecular Systems, Piscataway, United States: IEEE Press, 2006, p. 620-622, article id 4135031Conference paper (Refereed)
    Abstract [en]

    We present the ECs Sixth Framework Programme PARNASS project, which stands for 'Parallel nano assembling directed by short-range field forces' and represents a radical innovative approach to fabricating large volumes of hybrid nano electronic devices. The project combines in a synergy the 'top-down' and 'bottom-up' methods addressing one of the challenging physical and engineering problems of the very high accuracy over a large area. An array of specially designed nano-scale force field sources has to be a key part of this innovative approach to large-scale nano manufacturing. © 2006 IEEE.

  • 14.
    Borschel, Christian
    et al.
    Institute for Solid State Physics, Jena University, Max-Wien-Platz 1, 07743 Jena, Germany.
    Messing, Maria
    Avd. f. Fasta tillståndets fysik, Lunds Universitet.
    Borgström, Magnus T.
    Avd. f. Fasta tillståndets fysik, Lunds Universitet.
    Paschoal, Waldomiro
    Avd. f. Fasta tillståndets fysik, Lunds Universitet / Tillämpad matematik och fysik (MPE-lab), MPE-lab.
    Wallentin, Jesper
    Avd. f. Fasta tillståndets fysik, Lunds Universitet.
    Kumar, Sandeep
    Avd. f. Fasta tillståndets fysik, Lunds Universitet.
    Mergenthaler, Kilian
    Avd. f. Fasta tillståndets fysik, Lunds Universitet.
    Deppert, Knut
    Avd. f. Fasta tillståndets fysik, Lunds Universitet.
    Canali, C. M.
    Högskolan i Kalmar.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Samuelson, Lars
    Avd. f. Fasta tillståndets fysik, Lunds Universitet.
    Ronning, Carsten
    Institute for Solid State Physics, Jena University, Max-Wien-Platz 1, 07743 Jena, Germany.
    A New Route toward Semiconductor Nanospintronics: Highly Mn-Doped GaAs Nanowires Realized by Ion-Implantation under Dynamic Annealing Conditions2011In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 11, no 9, p. 3935-3940Article in journal (Refereed)
    Abstract [en]

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

  • 15.
    Borschel, Christian
    et al.
    Institute for Solid State Physics, University of Jena, Jena, Germany.
    Messing, Maria
    Lund University, Lund, Sweden.
    Mergenthaler, Kilian
    Lund University, Lund, Sweden.
    Borgström, Magnus T.
    Lund University, Lund, Sweden.
    Paschoal, Waldomiro
    Lund University, Lund, Sweden.
    Wallentin, Jesper
    Lund University, Lund, Sweden.
    Kumar, Sandeep
    Lund University, Lund, Sweden.
    Deppert, Knut
    Lund University, Lund, Sweden.
    Canali, Carlo
    Linnaeus University, Kalmar, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Samuelson, Lars
    Lund University, Lund, Sweden.
    Ronning, Carsten
    Institute for Solid State Physics, University of Jena, Jena, Germany.
    A New Route towards Semiconductor Nanospintronics: Highly Mn-Doped GaAs Nanowires Realized by Ion-Implantation under Dynamic Annealing Conditions2011Conference paper (Refereed)
  • 16.
    Chalangar, Ebrahim
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Department of Science and Technology, Linköping University, Norrköping, Sweden.
    Nur, Omer
    Department of Science and Technology, Linköping University, Norrköping, Sweden.
    Willander, Magnus
    Department of Science and Technology, Linköping University, Norrköping, Sweden.
    Gustafsson, Anders
    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. Department of Science and Technology, Linköping University, Norrköping, Sweden & Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Synthesis of Vertically Aligned ZnO Nanorods Using Sol-gel Seeding and Colloidal Lithography Patterning2021In: Nanoscale Research Letters, ISSN 1931-7573, E-ISSN 1556-276X, Vol. 16, no 1, article id 46Article in journal (Refereed)
    Abstract [en]

    Different ZnO nanostructures can be grown using low-cost chemical bath deposition. Although this technique is cost-efficient and flexible, the final structures are usually randomly oriented and hardly controllable in terms of homogeneity and surface density. In this work, we use colloidal lithography to pattern (100) silicon substrates to fully control the nanorods' morphology and density. Moreover, a sol-gel prepared ZnO seed layer was employed to compensate for the lattice mismatch between the silicon substrate and ZnO nanorods. The results show a successful growth of vertically aligned ZnO nanorods with controllable diameter and density in the designated openings in the patterned resist mask deposited on the seed layer. Our method can be used to fabricate optimized devices where vertically ordered ZnO nanorods of high crystalline quality are crucial for the device performance. © 2021 BioMed Central Ltd

  • 17.
    Conache, Gabriela
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Gray, Struan M.
    Avd. f. Fasta tillståndets fysik, Lunds Universitet.
    Bordag, Michael
    Institute for Theoretical Physics, Leipzig University.
    Ribayrol, Aline
    Avd. f. Fasta tillståndets fysik, Lunds Universitet.
    Fröberg, Linus
    Avd. f. Fasta tillståndets fysik, Lunds Universitet.
    Samuelson, Lars
    Avd. f. Fasta tillståndets fysik, Lunds Universitet.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Montelius, Lars
    Avd. f. Fasta tillståndets fysik, Lunds Universitet.
    AFM-based manipulation of InAs nanowires2008In: Proceedings of the IVC-17 (17th International Vacuum Congress) [also] ICSS-13 (13th International Conference on Surface Science) [also] ICN+T-2007 (International Conference on Nanoscience and Technology): 2-6 July 2007, Stockholm, Sweden, Bristol: Institute of Physics (IOP), 2008, Vol. 100, no 5, 1, p. 052051-052051-4Conference paper (Refereed)
    Abstract [en]

    A controlled method of manipulation of nanowires was found using the tip of an Atomic Force Microscope (AFM). Manipulation is done in the ‘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. Using this method, we have studied InAs nanowires on different substrates. We have also investigated interactions between wires and with gold features patterned onto the substrates.

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  • 18.
    Conache, Gabriela
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Gray, Struan M.
    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.
    Pettersson, Håkan
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Comparative friction measurements of InAs nanowires on three substrates2010In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, no 9, p. 094307-094307-5Article in journal (Refereed)
    Abstract [en]

    We have investigated friction between InAs nanowires and three different substrates: SiO2, fluorosilanized SiO2, and Si3N4. The nanowires were pushed laterally with the tip of an atomic force microscope and the friction force per unit length for both static and sliding friction was deduced from the equilibrium shape of the bent wires. On all three substrates, thick wires showed a difference between sliding and static friction of up to three orders of magnitude. Furthermore, all substrates display a transition to stick-slip motion for nanowires with a diameter of less than about 40 nm. Hydrophobic and hydrophilic substrates display similar friction behavior suggesting that a condensed water layer does not strongly influence our results. The patterns and trends in the friction data are similar for all three substrates, which indicates that they are more fundamental in character and not specific to a single substrate. ©2010 American Institute of Physics.

  • 19.
    Conache, Gabriela
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Lund University, Solid State Physics/Nanometer Consortium, Box 118, S-221 00, Lund, Sweden.
    Gray, Struan M.
    Lund University, Solid State Physics/Nanometer Consortium, Box 118, S-221 00, Lund, Sweden.
    Ribayrol, Aline
    Lund University, Solid State Physics/Nanometer Consortium, Box 118, S-221 00, Lund, Sweden.
    Fröberg, Linus
    Lund University, Solid State Physics/Nanometer Consortium, Box 118, S-221 00, Lund, Sweden.
    Samuelson, Lars
    Lund University, Solid State Physics/Nanometer Consortium, Box 118, S-221 00, Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Montelius, Lars
    Lund University, Solid State Physics/Nanometer Consortium, Box 118, S-221 00, Lund, Sweden.
    Nanowire friction with an applied bias2009Conference paper (Refereed)
    Abstract [en]

    Recently, we have shown how the friction acting on nanowires pushed across a surface by an AFM tip can be determined by measuring the radius of curvature of the bent wire aŸer manipulation. This technique allows us to study the friction properties of an extended mesoscale contact. Our main focus has been to determine whether such contacts behave like macroscopic objects, in which dišerences between the 'true' and 'apparent' contact areas play a key role and friction varies linearly with the applied normal force, or whether they are more like atomic-scale point contacts, wheremore fundamental processes dominate and friction oŸen is independent of the normal force. In this work we show how the friction between InAs nanowires and an insulating silicon nitride layer on a conductive silicon substrate varies when a DC voltage is applied to the AFM tip during manipulation. e tip charges the capacitor formed by the wire and the grounded silicon back contact, giving rise to attractive Coulomb forces and thus increasing the contact pressure between the wire and the silicon nitride. In this way we can vary the normal force on the sliding surfaces using a single wire, with a constant structure and contact geometry. Using nanowires of about 40-50 nm diameter and a few microns in length we have applied tip voltages in the range +12 to -12 V. Simplemodeling indicates that these voltages su›ce to give similar levels of band-lling and depletion to when the same wires are used in working wrap-gate or back-gate devices. A monotonic increase of the sliding friction with the voltage applied on the tip was observed. is implies that the friction increases with the normal force and that this mesoscopic system behaves more like a macroscopic contact, despite the nanometer size of the contact in the direction of motion.

  • 20.
    Conache, Gabriela
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Ribayrol, Aline
    Avd. f. Fasta Tillståndets Fysik, Lunds Universitet, Sweden.
    Fröberg, Linus
    Avd. f. Fasta Tillståndets Fysik, Lunds Universitet, Sweden.
    Borgström, Magnus T.
    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.
    Pettersson, Håkan
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Gray, Struan M.
    Avd. f. Fasta Tillståndets Fysik, Lunds Universitet, Sweden.
    Bias-controlled friction of InAs nanowires on a silicon nitride layer studied by atomic force microscopy2010In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 82, no 3Article in journal (Refereed)
    Abstract [en]

    By studying how nanowires lying on a surface bend when pushed by an atomic force microscopy tip we are able to measure the friction between them and the substrate. Here, we show how the friction between InAs nanowires and an insulating silicon nitride layer varies when a dc voltage is applied to the tip during manipulation. The bias charges the capacitor formed by the wire and the grounded silicon back contact. Electrostatic forces increase the contact pressure and allow us to tune the friction between the wire and the silicon nitride surface. Using nanowires of about 40-70 nm diameter and a few microns in length we have applied biases in the range +12 to -12 V. A monotonic increase of the sliding friction with voltage was observed. This increase in friction with the normal force implies that the mesoscopic nanowire-surface system behaves like a macroscopic contact, despite the nanometer size of the contact in the direction of motion. The demonstrated bias-controlled friction has potential applications in MEMS/NEMS devices.

  • 21.
    Corrêa Jr, Gregório B.
    et al.
    Instituto Federal de Educação, Ciência e Tecnologia do Pará, Abaetetuba, PA, Brazil & Programa de Pós-Graduação em Física, Universidade Federal do Pará, Belém, PA, Brazil & .
    Kumar, Sandeep
    Department of Physics, Central University of Rajasthan, Ajmer, India.
    Paschoal Jr, Waldomiro
    Programa de Pós-Graduação em Física, Universidade Federal do Pará, Belém, PA, Brazil.
    Devi, Chandni
    Department of Physics, Central University of Rajasthan, Ajmer, India.
    Jacobsson, Daniel
    Department of Chemistry, Lund University, Lund, Sweden.
    Johannes, Andreas
    Institut für Festkörperphysik, Friedrich-Schiller-Universität Jena, Jena, Germany.
    Ronning, Carsten
    Institut für Festkörperphysik, Friedrich-Schiller-Universität Jena, Jena, Germany.
    Pettersson, Håkan
    Halmstad University, School of Information Technology. Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Paraguassu, Waldeci
    Programa de Pós-Graduação em Física, Universidade Federal do Pará, Belém, PA, Brazil.
    Raman characterization of single-crystalline Ga0.96Mn0.04As:Zn nanowires realized by ion-implantation2019In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 30, no 33, article id 335202Article in journal (Refereed)
    Abstract [en]

    Recent progress in the realization of magnetic GaAs nanowires (NWs) doped with Mn has attracted a lot of attention due to their potential application in spintronics. In this work, we present a detailed Raman investigation of the structural properties of Zn doped GaAs (GaAs:Zn) and Mn-implanted GaAs:Zn (Ga0.96Mn0.04As:Zn) NWs. A significant broadening and redshift of the optical TO and LO phonon modes are observed for these NWs compared to as-grown undoped wires, which is attributed to strain induced by the Zn/Mn doping and to the presence of implantation-related defects. Moreover, the LO phonon modes are strongly damped, which is interpreted in terms of a strong LO phonon-plasmon coupling, induced by the free hole concentration. Moreover, we report on two new interesting Raman phonon modes (191 and 252 cm −1) observed in Mn ion-implanted NWs, which we attribute to Eg (TO) and A1g (LO) vibrational modes in a sheet layer of crystalline arsenic present on the surface of the NWs. This conclusion is supported by fitting the observed Raman shifts for the SO phonon modes to a theoretical dispersion function for a GaAs NW capped with a dielectric shell. © 2019 IOP Publishing Ltd.

  • 22.
    Devi, Chandni
    et al.
    Department of Physics, Central University of Rajasthan, Ajmer, India.
    Singhal, Rahul
    Department of Physics, Malaviya National Institute of Technology, Jaipur, India.
    Silva, Kleber Da
    Centro de Ciências Naturais e Tecnologia;, Universidade Do Estado Do Pará, Belém, PA, Brazil.
    Paschoal, Waldomiro
    Programa de Pós-Graduação em Física, Universidade Federal Do Pará, Belém, PA, Brazil.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS). Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Kumar, Sandeep
    Department of Physics, Central University of Rajasthan, Ajmer, India.
    Electrical transport properties of InAs nanowires synthesized by a solvothermal method2020In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 31, no 23, article id 235709Article in journal (Refereed)
    Abstract [en]

    Nanowires are widely considered to be key elements in future disruptive electronics and photonics. This paper presents the first detailed study of transport mechanisms in single-crystalline InAs nanowires synthesized by a cheap solvothermal wet chemical method. From detailed analyses of temperature-dependent current-voltage characteristics, it was observed that contacted nanowires operate in a linear transport regime at biases below a critical cross-over voltage. For larger biases, the transport changes to space-charge-limited conduction assisted by traps. The characteristic parameters such as free electron concentration, trap concentration and energy distribution, and electron mobility were all calculated. It was demonstrated that the nanowires have key electrical properties comparable to those of InAs nanowires grown by molecular beam epitaxy. Our results might pave the way for cheap disruptive low-dimensional electronics such as resistive switching devices. © 2020 IOP Publishing Ltd.

  • 23.
    Diao, Zhu
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Sauer, Vincent T. K.
    National Institute for Nanotechnology, Alberta, Canada; Department of Biological Sciences & Department of Electrical and Computer Engineering, University of Alberta, Alberta, Canada.
    Hiebert, Wayne K.
    National Institute for Nanotechnology, Alberta, Canada & Department of Physics, University of Alberta, Alberta, Canada.
    Integrated On-Chip Nano-Optomechanical Systems2017In: International Journal of High Speed Electronics and Systems, ISSN 0129-1564, Vol. 26, no 1-2, article id 1740005Article in journal (Refereed)
    Abstract [en]

    Recent developments in integrated on-chip nano-optomechanical systems are reviewed. Silicon-based nano-optomechanical devices are fabricated by a two-step process, where the first step is a foundry-enabled photonic circuits patterning and the second step involves in-house mechanical device release. We show theoretically that the enhanced responsivity of near-field optical transduction of mechanical displacement in on-chip nano-optomechanical systems originates from the finesse of the optical cavity to which the mechanical device couples. An enhancement in responsivity of more than two orders of magnitude has been observed when compared side-by-side with free-space interferometry readout. We further demonstrate two approaches to facilitate large-scale device integration, namely, wavelength-division multiplexing and frequency-division multiplexing. They are capable of significantly simplifying the design complexity for addressing individual nano-optomechanical devices embedded in a large array. © 2017 World Scientific Publishing Company.

  • 24.
    Gooth, Johannes
    et al.
    Institute of Nanostructure and Solid State Physics, Universität Hamburg, Hamburg, Germany & IBM Research-Zurich, Rüschlikon, Switzerland.
    Zierold, Robert
    Institute of Nanostructure and Solid State Physics, Universität Hamburg, Hamburg, Germany.
    Sergelius, Philip
    Institute of Nanostructure and Solid State Physics, Universität Hamburg, Hamburg, Germany.
    Hamdou, Bacel
    Institute of Nanostructure and Solid State Physics, Universität Hamburg, Hamburg, Germany.
    Garcia, Javier
    Institute for Metallic Materials, IFW Dresden, Dresden, Germany.
    Damm, Christine
    Institute for Metallic Materials, IFW Dresden, Dresden, Germany.
    Rellinghaus, Bernd
    Institute for Metallic Materials, IFW Dresden, Dresden, Germany.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Division of Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Pertsova, Anna
    Department of Physics and Electrical Engineering, Linnaeus University, Kalmar, Sweden.
    Canali, Carlo
    Department of Physics and Electrical Engineering, Linnaeus University, Kalmar, Sweden.
    Borg, Mattias
    IBM Research-Zurich, Rüschlikon, Switzerland.
    Nielsch, Kornelius
    Institute of Nanostructure and Solid State Physics, Universität Hamburg, Hamburg, Germany & Institute for Metallic Materials, IFW Dresden, Dresden, Germany.
    Local Magnetic Suppression of Topological Surface States in Bi2Te3 Nanowires2016In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 10, no 7, p. 7180-7188Article in journal (Refereed)
    Abstract [en]

    Locally induced, magnetic order on the surface of a topological insulator nanowire could enable room-temperature topological quantum devices. Here we report on the realization of selective magnetic control over topological surface states on a single facet of a rectangular Bi2Te3 nanowire via a magnetic insulating Fe3O4 substrate. Low-temperature magnetotransport studies provide evidence for local time-reversal symmetry breaking and for enhanced gapping of the interfacial 1D energy spectrum by perpendicular magnetic-field components, leaving the remaining nanowire facets unaffected. Our results open up great opportunities for development of dissipation-less electronics and spintronics. © 2016 American Chemical Society.

  • 25.
    Hajji, Maryam
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE).
    A comparative study of Nanowire-based InP and Planar ITO/InP Photodetectors2011Independent thesis Advanced level (degree of Master (One Year)), 15 credits / 22,5 HE creditsStudent thesis
    Abstract [en]

    Photodetectors are a kind of semiconductor devices that convert incoming light to an electrical signal. Photodetectors have different applications in sensors and fiber optic communication systems, and medical diagnosis etc.

    In this project  Fourier Transform Infrared (FTIR) Spectroscopy is used to investigate a new version  of photodiodes for near-infrared radiation that is based on self-assembled semiconductor nanowires (NWs) which are grown directly on the substrate without any epi-layer. The spectrally resolved photocurrent (at different applied biases) and IV curves (in darkness and illumination) for different temperatures have been studied, respectively.

    The thesis work also includes a comparison to a planar photodetector based on Indium Tin Oxide (ITO) deposited directly on an InP substrate.

     

     

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  • 26.
    Hussain, Laiq
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS).
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Wang, Q.
    Acreo Swedish ICT AB, Kista, Sweden.
    Karim, A.
    Acreo Swedish ICT AB, Kista, Sweden.
    Anderson, J.
    Acreo Swedish ICT AB, Kista, Sweden.
    Jafari, Mehrdad
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Song, J.
    Center for Opto-Electronic Convergence Systems, Korea Institute of Science and Technology, Seoul, South Korea.
    Choi, W. J.
    Center for Opto-Electronic Convergence Systems, Korea Institute of Science and Technology, Seoul, South Korea.
    Han, I. K.
    Center for Opto-Electronic Convergence Systems, Korea Institute of Science and Technology, Seoul, South Korea.
    Lim, J. Y.
    Center for Opto-Electronic Convergence Systems, Korea Institute of Science and Technology, Seoul, South Korea.
    SWIR-LWIR Photoluminescence from Sb-based Epilayers Grown on GaAs Substrates by using MBE2018In: Journal of the Korean Physical Society, ISSN 0374-4884, E-ISSN 1976-8524, Vol. 73, no 11, p. 1604-1611Article in journal (Refereed)
    Abstract [en]

    Utilizing Sb-based bulk epilayers on large-scale low-cost substrates such as GaAs for fabricating infrared (IR) photodetectors is presently attracting significant attention worldwide. For this study, three sample series of GaAsxSb1−x, In1−xGaxSb, and InAsxSb1x with different compositions were grown on semi-insulating GaAs substrates by using molecular beam epitaxy (MBE) and appropriate InAs quantum dots (QDs) as a defect-reduction buffer layer. Photoluminescence (PL) signals from these samples were observed over a wide IR wavelength range from 2 μm to 12 μm in agreement with the expected bandgap, including bowing effects. In particular, interband PL signals from InAsxSb1−x and In1−xGaxSb samples even at room temperature show promising potential for IR photodetector applications.

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    fulltext
  • 27.
    Höglund, Linda
    et al.
    Acreo AB, Kista, Sweden.
    Holtz, Per-Olof
    Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, Sweden.
    Asplund, Carl
    IRnova, Kista, Sweden.
    Wang, Qin
    Acreo AB, Kista, Sweden.
    Almqvist, Susanne
    Acreo AB, Kista, Sweden.
    Malm, Hedda
    IRnova, Kista, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Andersson, Jan Yngve
    Acreo AB, Kista, Sweden.
    Dual source optical pumping experiments revealing the origin of low temperature photocurrent peaks in quantum dots-in-a-well infrared photodetectors2008Conference paper (Refereed)
  • 28.
    Höglund, Linda
    et al.
    Acreo AB, Kista, Sweden & Linköping University, Linköping, Sweden.
    Holtz, Per-Olof
    Linköping University, Linköping, Sweden.
    Asplund, Carl
    IRnova, Kista, Sweden.
    Wang, Qin
    Acreo AB, Kista, Sweden.
    Almqvist, Susanne
    Acreo AB, Kista, Sweden.
    Petrini, Erik
    Acreo AB, Kista, Sweden.
    Andersson, Jan Y.
    Acreo AB, Kista, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Lund University, Lund, Sweden.
    Tuning of the detection wavelength in quantum dots-in-a-well infrared photodetectors2008In: Proceedings of SPIE, 6940, Infrared Technology and Applications XXXIV, 694002, 2008, Vol. 6940, no 1-2, article id 694002Conference paper (Refereed)
    Abstract [en]

    In this study, bias mediated tuning of the detection wavelength within the infrared wavelength region is demonstrated for quantum dots-in-a-well (DWELL) infrared photodetectors. In DWELL structures, intersubband transitions in the conduction band occur from a discrete state in the quantum dot to a subband inthe quantum well. Compared to "conventional" quantum dot infrared photodetectors, where the transitions take place between different discrete bands in thequantum dots, new possibilities to tune the detection wavelength window are opened up, partly by varying the quantum dot energy levels and partly by adjusting the width and composition of the quantum well. In the DWELL structure used, an asymmetric positioning of the InAs quantum dot layer in a 8 nm wide In0.15Ga0.85As/GaAs QW has been applied which enables tuning of the peak detection wavelength within the long wavelength infrared (LWIR; 8 - 14 gm) region. When the applied bias was reversed, a wavelength shift from 8.5 to 9.5 mu m was observed for the peak position in the spectral response. For another DWELL structure, with a well width of 2 nm, the tuning range of the detector could be shifted from the medium wavelength infrared (MWIR; 3-5 mu m) region to the LWIR region. With small changes in the applied bias, the peak detection wavelength could be shifted from 5.1 to 8 mu m. These tuning properties ofDWELL structures could be essential for applications such as modulators and two-colour infrared detection. © (2008) COPYRIGHT SPIE--The International Society for Optical Engineering.

  • 29.
    Höglund, Linda
    et al.
    Acreo AB, Kista, Sweden.
    Holtz, Per-Olof
    IFM, Linköping University, Linköping, Sweden.
    Asplund, Carl
    IRnova AB, Kista, Sweden.
    Wang, Qin
    Acreo AB, Kista, Sweden.
    Almqvist, Susanne
    Acreo AB, Kista, Sweden.
    Petrini, Erik
    Acreo AB, Kista, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Andersson, Jan Y.
    Acreo AB, Kista, Sweden.
    Voltage mediated tuning of the detection wavelength in quantum dots-in-a-well infrared photodetectors2008Conference paper (Refereed)
  • 30.
    Höglund, Linda
    et al.
    Industrial Nano- and Microtechnology, Acreo AB, Kista, Sweden.
    Holtz, Per-Olof
    Department of Physics, Chemistry and Biology (LFM), Linköping University, Linköping, Sweden.
    Ouattara, L.
    Synchrotron Radiation Research, Lund University, Lund, Sweden.
    Asplund, Carl
    IRnova, Kista, Sweden.
    Wang, Qin
    Industrial Nano- and Microtechnology, Acreo AB, Kista, Sweden.
    Almqvist, Susanne
    Industrial Nano- and Microtechnology, Acreo AB, Kista, Sweden.
    Petrini, Erik
    Industrial Nano- and Microtechnology, Acreo AB, Kista, Sweden.
    Malm, Hedda
    IRnova, Kista, Sweden.
    Borglind, J.
    Industrial Nano- and Microtechnology, Acreo AB, Kista, Sweden.
    Smuk, S.
    Industrial Nano- and Microtechnology, Acreo AB, Kista, Sweden.
    Mikkelsen, A.
    Synchrotron Radiation Research, Lund University, Lund, Sweden.
    Lundgren, E.
    Synchrotron Radiation Research, Lund University, Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Solid State Physics and the Nanometer Consortium, Lund University, Lund, Sweden.
    Andersson, Jan Y.
    Industrial Nano- and Microtechnology, Acreo AB, Kista, Sweden.
    Quantum dots-in-a-well infrared photodetectors for long wavelength infrared detection2006In: Proceedings of SPIE: The International Society for Optical Engineering / [ed] James G. Grate, Francois Kajzar & Mikael lindgren, Bellingham, Wash.: SPIE - International Society for Optical Engineering, 2006, p. U51-U63Conference paper (Refereed)
    Abstract [en]

    We report on a quantum dots-in-a-well infrared photodetector (DWELL QDIP) grown by metal organic vapor phase epitaxy. The DWELL QDIP consisted of ten stacked InAs/In0.5Ga0.85As/GaAs QD layers embedded between n-doped contact layers. The density of the QDs was about 9 × 10 10 cm-2 per QD layer. The energy level structure of the DWELL was revealed by optical measurements of interband transitions, and from a comparison with this energy level scheme the origin of the photocurrent peaks could be identified. The main intersubband transition contributing to the photocurrent was associated with the quantum dot ground state to the quantum well excited state transition. The performance of the DWELL QDIPs was evaluated regarding responsivity and dark current for temperatures between 15 K and 77 K. The photocurrent spectrum was dominated by a LWIR peak, with a peak wavelength at 8.4 μm and a full width at half maximum (FWHM) of 1.1 μm. At an operating temperature of 65 K, the peak responsivity was 30 mA/W at an applied bias of 4 V and the dark current was 1.2×10-5 A/cm2. Wavelength tuning from 8.4 μm to 9.5 μm was demonstrated, by reversing the bias of the detector.

  • 31.
    Höglund, Linda
    et al.
    Acreo AB.
    Karlsson, Fredrik
    IFM, Linköping University.
    Holtz, Per-Olof
    IFM, Linköping University.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Pistol, Mats-Erik
    Avd. f. Fasta Tillståndets Fysik, Lunds Universitet.
    Wang, Qin
    Acreo AB.
    Almqvist, Susanne
    Acreo AB.
    Asplund, Carl
    IRnova.
    Malm, Hedda
    IRnova.
    Petrini, Erik
    Acreo AB.
    Andersson, Jan
    Acreo AB.
    Energy level scheme of InAs/InxGa1-xAs/GaAs quantum-dots-in-a-well infrared photodetector structures2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 3, p. 035314-Article in journal (Refereed)
    Abstract [en]

    A thorough investigation of quantum-dots-in-a-well structures for infrared photodetector applications has been performed employing different experimental techniques. The electronic structure of self-assembled InAs quantum dots embedded in an In0.15Ga0.85As/GaAs quantum well (QW) was deduced from photoluminescence (PL) and PL excitation (PLE) spectroscopy. From polarization-dependent PL it was revealed that the quantum dots hold two electron energy levels and two heavy-hole levels. Tunnel capacitance spectroscopy confirmed an electron energy level separation of about 50 meV, and additionally, that the conduction-band ground state and excited state of the dots are twofold and fourfold degenerates, respectively. Intersubband photocurrent spectroscopy, combined with simultaneous interband pumping of the dots, revealed a dominant transition at 150 meV (8.5 mu m) between the ground state of the quantum dots and the excited state of the QW. Results from detailed full three-dimensional calculations of the electronic structure, including effects of composition intermixing and interdot interactions, confirm the experimentally unravelled energy level scheme of the dots and well.

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  • 32.
    Iakovleva, Natalia
    et al.
    Petrozavodsk State University, Russia.
    Kokatev, Alexander
    Petrozavodsk State University.
    Pettersson, Håkan
    Petrozavodsk State University, Russia.
    Savchenko, O.
    Petrozavodsk State University, Russia.
    Iakovlev, A.
    Petrozavodsk State University, Russia.
    Chupakhina, E.
    Petrozavodsk State University, Russia.
    Suomolajnen, K.
    Petrozavodsk State University, Russia.
    Stepanova, K.
    Petrozavodsk State University, Russia.
    Khanina, E.
    Petrozavodsk State University, Russia.
    Self-organized porous anodic oxide matrix and nanocomposite materials on their base2011Conference paper (Refereed)
  • 33.
    Jacobsson, Emilia
    et al.
    Halmstad University, School of Education, Humanities and Social Science.
    Bengtsson, Viktoria
    Halmstad University, School of Education, Humanities and Social Science.
    “Denna var ju magnetisk”: En learning study om storytelling och barns förståelse av magnetism2023Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Syftet med studien är att genom en learning study bidra med kunskap om hur storytelling är en relevant strategi för att stärka barns kunskap om magnetism. Studien genomfördes med barn mellan 4-6 år som deltagit i undervisningssituationer med storytelling och praktiska aktiviteter med magnetism som lärandeobjekt. Empirin som samlats in genom ljud- och videoinspelning har analyserats genom interaktionsanalys. En learning study lägger stor vikt vid sambandet mellan individers interaktion med valt lärandeobjekt och kritiska aspekter. Resultatet är att den kritiska aspekten omagnetiskt material nås med hjälp av storytelling, urskiljning och variation. Studiens resultat pekar även på att urskiljning av magnetiskt material kräver fler undervisningsmoment för att den kritiska aspekten ska bli förståelig för barnen. Slutligen visar studien på att storytelling har god potential som undervisningsstrategi i förskolan, men att det krävs god ämnesdidaktisk kunskap i syfte till att ge barnen möjlighet till rätt kunskap och utveckling om det fysikaliska fenomenet magnetism.

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  • 34.
    Jafari Jam, Reza
    Lund University, Lund, Sweden.
    Gold Electrodeposition in Semiconductor Nanowire Technology2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Semiconductor nanowires are widely considered as promising candidates for next generations of electronics and optoelectronics. Gold seed particles have so far been recognized as the most important catalyst for growth of nanowires. Costs related to substrates, lithography processes and gold consumption most strongly influence the final cost of nanowire-based devices. An optimum gold deposition process can facilitate re-use of substrates, avoid repetitive lithogra-phy processes and reduce the gold consumption in order to reduce the cost of the final device. In this work, we report on nanowire seed definition by gold electrodeposition. Electron microscopy inspection and optical spectroscopy confirm that the subsequently grown III-V nanowires have surface morphology and crystal quality comparable to those of nanowires grown from seed particles defined by conventional thermal evaporation. For seeding of substrates used in a typical growth run, we used around 650 times less gold with a 10 times higher throughput as compared to thermal evaporation. Using selective gold electrodeposition, we demonstrated redeposition of seed particles on a substrate after nanowire peel-off in order to reuse it for multiple growth runs. We also demonstrated the possibility of depositing seed particles in deep holes etched in thick masks to facilitate template-assisted growth of nanowires on (001) substrates.

  • 35.
    Jafari Jam, Reza
    et al.
    Division of Solid State Physics/Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Heurlin, Magnus
    Division of Solid State Physics/Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Jain, Vishal
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS). Division of Solid State Physics/Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Kvennefors, Anders
    Division of Solid State Physics/Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Graczyk, Mariusz
    Division of Solid State Physics/Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Maximov, Ivan
    Division of Solid State Physics/Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Borgström, Magnus T.
    Division of Solid State Physics/Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Division of Solid State Physics/Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Samuelson, Lars
    Division of Solid State Physics/Nanometer Structure Consortium, Lund University, Lund, Sweden.
    III-V nanowire synthesis by use of electrodeposited gold particles2015In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 15, no 1, p. 134-138Article in journal (Refereed)
    Abstract [en]

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

  • 36.
    Jain, Vishal
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Heurlin, Magnus
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Barrigon, Enrique
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Bosco, Lorenzo
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Nowzari, Ali
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Schroff, Shishi
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Boix, Virginia
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Karimi, Mohammad
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Jafari Jam, Reza
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Berg, Alexander
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Samuelson, Lars
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Borgström, Magnus T.
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Capasso, Federico
    School of Engineering and Applied Sciences, Harvard University, Cambridge, United States.
    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.
    InP/InAsP Nanowire-Based Spatially Separate Absorption and Multiplication Avalanche Photodetectors2017In: ACS Photonics, E-ISSN 2330-4022, Vol. 4, no 11, p. 2693-2698Article in journal (Refereed)
    Abstract [en]

    Avalanche photodetectors (APDs) are key components in optical communication systems due to their increased photocurrent gain and short response time as compared to conventional photodetectors. A detector design where the multiplication region is implemented in a large band gap material is desired to avoid detrimental Zener tunneling leakage currents, a concern otherwise in smaller band gap materials required for absorption at 1.3/1.55 μm. Self-assembled III-V semiconductor nanowires offer key advantages such as enhanced absorption due to optical resonance effects, strain-relaxed heterostructures, and compatibility with mainstream silicon technology. Here, we present electrical and optical characteristics of single InP and InP/InAsP nanowire APD structures. Temperature-dependent breakdown characteristics of p+-n-n+ InP nanowire devices were investigated first. A clear trap-induced shift in breakdown voltage was inferred from I-V measurements. An improved contact formation to the p+-InP segment was observed upon annealing, and its effect on breakdown characteristics was investigated. The band gap in the absorption region was subsequently varied from pure InP to InAsP to realize spatially separate absorption and multiplication APDs in heterostructure nanowires. In contrast to the homojunction APDs, no trap-induced shifts were observed for the heterostructure APDs. A gain of 12 was demonstrated for selective optical excitation of the InAsP segment. Additional electron-beam-induced current measurements were carried out to investigate the effect of local excitation along the nanowire on the I-V characteristics. Simulated band profiles and electric field distributions support our interpretation of the experiments. Our results provide important insight for optimization of avalanche photodetector devices based on III-V nanowires. © 2017 American Chemical Society

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  • 37.
    Jain, Vishal
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Solid State Physics and Nano, Lund University, Lund, Sweden.
    Heurlin, Magnus
    Solid State Physics and Nano, Lund University, Lund, Sweden.
    Karimi, Mohammad
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Solid State Physics and Nano, Lund University, Lund, Sweden.
    Hussain, Laiq
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Solid State Physics and Nano, Lund University, Lund, Sweden.
    Aghaeipour, Mahtab
    Solid State Physics and Nano, Lund University, Lund, Sweden.
    Nowzari, Ali
    Solid State Physics and Nano, Lund University, Lund, Sweden.
    Berg, Alexander
    Solid State Physics and Nano, Lund University, Lund, Sweden.
    Nylund, Gustav
    Solid State Physics and Nano, Lund University, Lund, Sweden.
    Capasso, Federico
    Harvard University, Cambridge, United States of America.
    Samuelson, Lars
    Solid State Physics and Nano, Lund University, Lund, Sweden.
    Borgström, Magnus T.
    Solid State Physics and Nano, 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 Nano, Lund University, Lund, Sweden.
    Bias-dependent spectral tuning in InP nanowire-based photodetectors2017In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 28, no 11, article id 114006Article in journal (Refereed)
    Abstract [en]

    Nanowire array ensembles contacted in a vertical geometry are extensively studied and considered strong candidates for next generations of industrial scale optoelectronics. Key challenges in this development deal with optimization of the doping profile of the nanowires and the interface between nanowires and transparent top contact. Here we report on photodetection characteristics associated with doping profile variations in InP nanowire array photodetectors. Bias-dependent tuning of the spectral shape of the responsivity is observed which is attributed to a Schottky-like contact at the nanowire-ITO interface. Angular dependent responsivity measurements, compared with simulated absorption spectra, support this conclusion. Furthermore, electrical simulations unravel the role of possible self-gating effects in the nanowires induced by the ITO/SiOx wrap-gate geometry. Finally, we discuss possible reasons for the observed low saturation current at large forward biases.  

  • 38.
    Jain, Vishal
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Heurlin, Magnus
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Lindgren, David
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Nowzari, Ali
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Hussein, Laiq
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Wallentin, Jesper
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Capasso, Federico
    School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA.
    Borgström, Magnus T.
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Gustafsson, Anders
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Samuelson, Lars
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Large area photodetectors based on InP NWs with InAs/InAsP QWs2014Conference paper (Refereed)
    Abstract [en]

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

  • 39.
    Jain, Vishal
    et al.
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Heurlin, Magnus
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Nowzari, Ali
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Lindgren, David
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Borgström, Magnus T.
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Capasso, Federico
    School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA.
    Samuelson, Lars
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Pettersson, Håkan
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Large Area Photodetectors at 1.3/1.55 μm Based on InP/InAsP NWs2014Conference paper (Refereed)
    Abstract [en]

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

  • 40.
    Jain, Vishal
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Wallentin, Jesper
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Nowzari, Ali
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Heurlin, Magnus
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Asoli, Damir
    Sol Voltaics AB, Lund, Sweden.
    Borgström, Magnus T.
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Capasso, Federico
    School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA.
    Samuelson, Lars
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Pettersson, Håkan
    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.
    Processing and Characterization of Nanowire Arrays for Photodetectors2015In: Nano-Structures for Optics and Photonics: Optical Strategies for Enhancing Sensing, Imaging, Communication and Energy Conversion / [ed] Baldassare Di Bartolo, John Collins & Luciano Silvestri, Dordrecht: Springer, 2015, p. 511-512Conference paper (Refereed)
    Abstract [en]

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

  • 41.
    Jam, Reza Jafari
    et al.
    Lund Univ, Div Solid State Phys & NanoLund, Box 118, SE-21100 Lund, Sweden..
    Persson, Axel R.
    Lund Univ, Centr & Anal & Synth & NanoLund, POB 124, SE-21100 Lund, Sweden..
    Barrigon, Enrique
    Lund Univ, Div Solid State Phys & NanoLund, Box 118, SE-21100 Lund, Sweden..
    Heurlin, Magnus
    Lund Univ, Div Solid State Phys & NanoLund, Box 118, SE-21100 Lund, Sweden..
    Geijselaers, Irene
    Lund Univ, Div Solid State Phys & NanoLund, Box 118, SE-21100 Lund, Sweden..
    Gomez, Victor J.
    Lund Univ, Div Solid State Phys & NanoLund, Box 118, SE-21100 Lund, Sweden..
    Hultin, Olof
    RISE Res Inst Sweden, Scheelevagen 17, S-22370 Lund, Sweden..
    Samuelson, Lars
    Lund Univ, Div Solid State Phys & NanoLund, Box 118, SE-21100 Lund, Sweden..
    Borgstrom, Magnus T.
    Lund Univ, Div Solid State Phys & NanoLund, Box 118, SE-21100 Lund, Sweden..
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Lund Univ, Div Solid State Phys & NanoLund, Box 118, SE-21100 Lund, Sweden.;Halmstad Univ, Sch Informat Technol, Box 823, S-30118 Halmstad, Sweden..
    Template-assisted vapour-liquid-solid growth of InP nanowires on (001) InP and Si substrates2020In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 12, no 2, p. 888-894Article in journal (Refereed)
    Abstract [en]

    We report on the synthesis of vertical InP nanowire arrays on (001) InP and Si substrates using template-assisted vapour-liquid-solid growth. A thick silicon oxide layer was first deposited on the substrates. The samples were then patterned by electron beam lithography and deep dry etching through the oxide layer down to the substrate surface. Gold seed particles were subsequently deposited in the holes of the pattern by the use of pulse electrodeposition. The subsequent growth of nanowires by the vapour-liquid-solid method was guided towards the [001] direction by the patterned oxide template, and displayed a high growth yield with respect to the array of holes in the template. In order to confirm the versatility and robustness of the process, we have also demonstrated guided growth of InP nanowire p-n junctions and InP/InAs/InP nanowire heterostructures on (001) InP substrates. Our results show a promising route to monolithically integrate III-V nanowire heterostructure devices with commercially viable (001) silicon platforms.

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  • 42.
    Janousch, Markus
    et al.
    Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland.
    Meijer, G. Ingmar
    IBM Research, Zurich Research Laboratory, Rüschlikon, Switzerland.
    Staub, Urs
    Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland.
    Delley, Bernard
    Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland.
    Karg, Siegfried F.
    IBM Research, Zurich Research Laboratory, Rüschlikon, Switzerland.
    Andreasson, Björn Pererik
    Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland.
    Role of oxygen vacancies in cr-doped SrTiO3 for resistance-change memory2007In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 19, no 17, p. 2232-2235Article in journal (Refereed)
    Abstract [en]

    A high density of oxygen vacancies has been found in an experiment to determine the path of electrical conduction in Cr-doped SrTiO3 memory cells. The Cr acts as a seed for the localization of oxygen vacancies, leading to a statistically homogeneous distribution of charge carriers within the path. This warrants a controllable doping profile and improved device scaling down to the nanometer scale. The combination of laterally resolved micro-X-ray absorption spectroscopy and thermal imaging concludes that the resistance switching in Cr-doped SrTiO3 originates from an oxygen-vacancy drift to/from the electrode that was used as anode during the conditioning process. The experiments shows that this oxygen vacancy concept is crucial for the entire class of transition-metal-oxide-based bipolar resistance-change memory.

  • 43.
    Jeddi Abdarloo, Hossein
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS). Lund University, Lund, Sweden.
    Karimi, Mohammad
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS). Lund University, Lund, Sweden.
    Witzigmann, Bernd
    University of Kassel, Kassel, Germany.
    Zeng, Xulu
    Lund University, Lund, Sweden.
    Hrachowina, Lukas
    Lund University, Lund, Sweden.
    Borgström, Magnus T.
    Lund University, Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS). Lund University, Lund, Sweden.
    Gain and bandwidth of InP nanowire array photodetectors with embedded photogated InAsP quantum discs2021In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 13, no 12, p. 6227-6233Article in journal (Refereed)
    Abstract [en]

    Here we report on the experimental results and advanced self-consistent real device simulations revealing a fundamental insight into the non-linear optical response of n+-i-n+ InP nanowire array photoconductors to selective 980 nm excitation of 20 axially embedded InAsP quantum discs in each nanowire. The optical characteristics are interpreted in terms of a photogating mechanism that results from an electrostatic feedback from trapped charge on the electronic band structure of the nanowires, similar to the gate action in a field-effect transistor. From detailed analyses of the complex charge carrier dynamics in dark and under illumination was concluded that electrons are trapped in two acceptor states, located at 140 and 190 meV below the conduction band edge, at the interface between the nanowires and a radial insulating SiOx cap layer. The non-linear optical response was investigated at length by photocurrent measurements recorded over a wide power range. From these measurements were extracted responsivities of 250 A W-1 (gain 320)@20 nW and 0.20 A W-1 (gain 0.2)@20 mW with a detector bias of 3.5 V, in excellent agreement with the proposed two-trap model. Finally, a small signal optical AC analysis was made both experimentally and theoretically to investigate the influence of the interface traps on the detector bandwidth. While the traps limit the cut-off frequency to around 10 kHz, the maximum operating frequency of the detectors stretches into the MHz region. © The Royal Society of Chemistry

  • 44.
    Jeddi Abdarloo, Hossein
    et al.
    Halmstad University, School of Information Technology. Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Witzigmann, Bernd
    Institute for Optoelectronics, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany.
    Adham, Kristi
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Hrachowina, Lukas
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Borgström, Magnus T.
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology. Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Spectrally Tunable Broadband Gate-All-Around InAsP/InP Quantum Discs-in-Nanowire Array Phototransistors with a High Gain-Bandwidth Product2023In: ACS Photonics, E-ISSN 2330-4022, Vol. 10, no 6, p. 1748-1755Article in journal (Refereed)
    Abstract [en]

    High-performance broadband photodetectors offering spectral tunability and a high gain-bandwidth product are crucial in many applications. Here, we report on a detailed experimental and theoretical study of three-terminal phototransistors comprised of three million InP nanowires with 20 embedded InAsP quantum discs in each nanowire. A global, transparent ITO gate all around the nanowires facilitates a radial control of the carrier concentration by more than two orders of magnitude. The transfer characteristics reveal two different transport regimes. In the subthreshold region, the photodetector operates in a diffusion mode with a distinct onset at the bandgap of InP. At larger gate biases, the phototransistor switches to a drift mode with a strong contribution from the InAsP quantum discs. Besides an unexpected spectral tunability, the detector exhibits a state-of-the-art responsivity, reaching around 100 A/W (638 nm/20 μW) @ VGS = 1.0 V/VDS = 0.5 V with a gain-bandwidth product of around 1 MHz, in excellent agreement with a comprehensive real-device model. © 2023 The Authors. Published by American Chemical Society.

  • 45.
    Johannes, Andreas
    et al.
    Institute for Solid State Physics, Friedrich-Schiller-University Jena, Jena, Germany.
    Noack, Stefan
    Institute for Solid State Physics, Friedrich-Schiller-University Jena, Jena, Germany.
    Paschoal Jr, Waldomiro
    Halmstad University, School of Information Technology. Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Kumar, Sandeep
    Halmstad University, School of Information Technology. Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Jacobsson, Daniel
    Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Pettersson, Håkan
    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.
    Samuelson, Lars
    Solid State Physics/The Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Dick, Kimberly A.
    Centre for Analysis and Synthesis, Lund University, Lund, Sweden.
    Martinez-Criado, G.
    European Synchrotron Radiation Facility, Grenoble, France.
    Burghammer, M.
    European Synchrotron Radiation Facility, Grenoble, France.
    Ronning, Carsten
    Institute for Solid State Physics, Friedrich-Schiller-University Jena, Jena, Germany.
    Enhanced sputtering and incorporation of Mn in implanted GaAs and ZnO nanowires2014In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 47, no 39, article id 394003Article in journal (Refereed)
    Abstract [en]

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

  • 46.
    Jorlöv, Sofia
    et al.
    Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS), Biomechanics and Biomedicine.
    Hammarström, Jessica
    Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS), Biomechanics and Biomedicine.
    Comparison Study of the Two Pediatric ATDs: Hybrid III 6-Year-Old and Q62011Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    As a new pediatric dummy family, the Q-family, is suggested for the European childsafety regulations (R44) and the updated EuroNCAP, it needed to be tested andcompared to the older pediatric dummy family, Hybrid III, used in testing at Autolivtoday.In this study, tests were performed with the Q6 and the Hybrid III 6-year-old. Bothdummies were subjected to eight sled tests using a EuroNCAP acceleration pulse. The sled represented the interior of a Volvo V70, with integrated booster cushions mounted onto the car body through a rigid fixture. Standard belt were used for all tests, except one where pretensioning was used. Static tests investigated how the chest deflection on Q6 was affected by the shoulder belt geometry. Large difference in belt interaction was observed between the dummies. The beltslipped off the Hybrid III’s shoulder for all tests except one, while the belt on the Qdummy’swas hard to provoke off the shoulder. The overall kinematic behavior, beforethe belt slipped off the Hybrid III’s shoulder, were similar for both dummies. Differences in chest deflection on the Q6, depending on the belt geometry, were observed in both the dynamic and the static tests; a shoulder belt geometry closer to theneck resulted in minor displacement than a mid-shoulder belt geometry. After testing, five different damages were observed on the Q6.

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  • 47.
    Jurgilaitis, A.
    et al.
    Department of Physics & MAX IV Laboratory, Lund University, Lund, Sweden.
    Enquist, H.
    MAX IV Laboratory, Lund University, Lund, Sweden.
    Andreasson, Björn Pererik
    Department of Physics, Lund University, Lund, Sweden.
    Persson, A. I. H.
    Department of Physics, Lund University, Lund, Sweden.
    Borg, B. M.
    Department of Electrical and Information Technology, Lund University, Lund, Sweden.
    Caroff, P.
    Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra, Australia.
    Dick, K. A.
    Department of Physics, Lund University, Lund, Sweden & Division of Polymer and Materials Chemistry, Department of Chemistry, Lund University, Lund, Sweden.
    Harb, M.
    Department of Physics & MAX IV Laboratory, Lund University, Lund, Sweden.
    Linke, H.
    Department of Physics, Lund University, Lund, Sweden.
    Nüske, R.
    Department of Physics, Lund University, Lund, Sweden.
    Wernersson, L.-E.
    Department of Electrical and Information Technology, Lund University, Lund, Sweden.
    Larsson, J.
    Department of Physics, Lund University, Lund, Sweden.
    Time-Resolved X-ray Diffraction Investigation of the Modified Phonon Dispersion in InSb Nanowires2014In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 14, no 2, p. 541-546Article in journal (Refereed)
    Abstract [en]

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

  • 48.
    Karimi, Mohammad
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Heurlin, Magnus
    Solid State Physics and NanoLund, Lund University, Lund, Sweden & Sol Voltaics AB, Lund, Sweden.
    Limpert, Steven
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Jain, Vishal
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Zeng, Xulu
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Geijselaers, Irene
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Nowzari, Ali
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Fu, Ying
    Department of Applied Physics, Royal Institute of Technology (KTH), Solna, Sweden.
    Samuelson, Lars
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Linke, Heiner
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Borgström, Magnus T.
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Intersubband Quantum Disc-in-Nanowire Photodetectors with Normal-Incidence Response in the Long-Wavelength Infrared2018In: Nano Letters, ISSN 1530-6984, E-ISSN 1530-6992, Vol. 18, no 1, p. 365-372Article in journal (Refereed)
    Abstract [en]

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

  • 49.
    Karimi, Mohammad
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Jain, Vishal
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Heurlin, Magnus
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Nowzari, Ali
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Hussain, Laiq
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS). Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Lindgren, David
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Stehr, Jan Eric
    Department of Physics, Chemistry and Biology, Linköping University, Linköping, Sweden.
    Buyanova, Irina A.
    Department of Physics, Chemistry and Biology, Linköping University, Linköping, Sweden.
    Gustafsson, Anders
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Samuelson, Lars
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Borgström, Magnus T.
    Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS). Solid State Physics and NanoLund, Lund University, Lund, Sweden.
    Room-temperature InP/InAsP Quantum Discs-in-Nanowire Infrared Photodetectors2017In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 17, no 6, p. 3356-3362Article in journal (Refereed)
    Abstract [en]

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

  • 50.
    Karthik, K. R. G.
    et al.
    School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore.
    Andreasson, Björn Pererik
    School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore.
    Sun, C.
    School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore.
    Pramana, S. S.
    School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore.
    Varghese, B.
    Department of Physics, National University of Singapore, Singapore, Singapore.
    Sow, C. H.
    Department of Physics, National University of Singapore, Singapore, Singapore.
    Mathews, N.
    School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore.
    Wong, L. H.
    School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore.
    Mhaisalkar, S. G.
    School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore.
    Physical and Electrical Properties of Single Zn2SnO4 Nanowires2011In: Electrochemical and solid-state letters, ISSN 1099-0062, E-ISSN 1944-8775, Vol. 14, no 1, p. K5-K7Article in journal (Refereed)
    Abstract [en]

    Electrical characterizations of single Zn2SnO4 (ZTO) nanowire devices are presented. These include resistivity, mobility, and photosensing measurements. The resistivity and the mobility of the Zn2SnO4 nanowire were measured to be 5.6 cm and 0.2 cm2/Vs, respectively. These values were found to be strongly dependent on the amount of electron-donating defects and less dependent on the thickness of the nanowires. An increase in the resistivity when changing the ambient atmosphere is observed. This change is caused by defect states lying in the bandgap, as shown by photoluminescence. The results imply the potential of ZTO nanowires as phototransistors and other photosensitive devices. © 2010 The Electrochemical Society.

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