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High resolution strain mapping of a single axially heterostructured nanowire using scanning X-ray diffraction

Nano Research 2020年第9期13卷 2460-2468页

作者： Susanna Hammarberg Vilgaile Dagyte Lert Chayanun Megan O.Hill Alexander Wyke Alexander Bjorling Ulf Johansson Sebastian Kalbfleisch magnus Heurlin Lincoln J.Lauhon magnus t.borgstrom Jesper Wallentin Synchrotron Radiation Research and NanoLund Lund UniversityBox 118Lund 22100Sweden Solid State Physics and NanoLund Lund UniversityBox 118Lund 22100Sweden Department of Materials Science and Engineering Northwestern UniversityEvanstonIllinois 60208USA MAX IV Laboratory Lund UniversityBox 118Lund 22100Sweden

Axially heterostructured nanowires are a promising platform for next generation electronic and optoelectronic *** based on theoretical modeling have predicted more complex strain distributions and increased critical layer thicknesses than in thin films,due to lateral strain relaxation at the surface,but the understanding of the growth and strain distributions in these complex structures is hampered by the lack of high-resolution characterization ***,we demonstrate strain mapping of an axially segmented GalnP-lnP 190 nm diameter nanowire heterostructure using scanning X-ray *** systematically investigate the strain distribution and lattice tilt in three different segment lengths from 45 to 170 nm,obtaining strain maps with about 10^-4 relative strain *** experiments were performed using the 90 nm diameter nanofocus at the NanoMAX beamline,taking advantage of the high coherent flux from the first diffraction limited storage ring MAX *** experimental results are in good agreement with a full simulation of the experiment based on a three-dimensional(3D)finite element *** largest segments show a complex profile,where the lateral strain relaxation at the surface leads to a dome-shaped strain distribution from the mismatched interfaces,and a change from tensile to compressive strain within a single *** lattice tilt maps show a cross-shaped profile with excellent qualitative and quantitative agreement with the *** contrast,the shortest measured InP segment is almost fully adapted to the surrounding GalnP segments.

关键词： strain mapping nanowire heterostructure X-ray diffraction(XRD) MAX IV finite element modeling

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InP/GaInP nanowire tunnel diodes

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Nano Research 2018年第5期11卷 2523-2531页

作者： Xulu Zeng Gaute Otnes magnus Heurlin Renato t Mourao magnus t.borgstrom Solid State Physics NanoLund Department of Physics Lund University P.O. Box 118 Lund 5E-22100 Sweden Instituto de Fisica Universidade Federal do Rio de Janeiro Caixa Postal 68528 Rio de Janeiro 21941-972 Brazil

Semiconductor nanowire （NW） solar cells with a single p-n junction have exhibited efficiency comparable to that of their planar counterparts with a substantial reduction in material consumption. tandem geometry is a path toward the fabrication of devices with even higher efficiencies, for which a key step is the fabrication of tunnel （Esaki） diodes within NWs with the correct diameter, pitch, and material combination for maximized efficiency. InP/GaInP and GaInP/InP NW tunnel diodes with band gap combinations corresponding to high-efficiency solar energy harvesting were fabricated and their electrical characteristics and material properties were compared. Four different configurations, with respect to material composition and doping, were investigated. the NW arrays were grown with metal-organic vapor-phase epitaxy from Au particles by use of nano-imprint lithography, metal evaporation and lift-off. Electrical measurements showed that the NWs behave as tunnel diodes in both InP （bottom）/GaInP （top） and GaInP （bottom）/InP （top） configurations, exhibiting a maximum peak current density of 25 A/cm^2, and maximum peak to valley current ratio of 2.5 at room temperature. the realization of NW tunnel diodes in both InP/GaInP and GaInP/InP configurations represent an opportunity for the use of NW tandem solar cells, whose efficiency is independent of the growth order of the different materials, increasing the flexibility regarding dopant incorporation polarity.

关键词： nanowire tunnel diode InP GaInP tandem junction solar cell

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Strategies to obtain pattern fidelity in nanowire growth from large-area surfaces patterned using nanoimprint lithography

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Nano Research 2016年第10期9卷 2852-2861页

作者： Gaute Otnes magnus Heurlin Mariusz Graczyk Jesper Wallentin Daniel Jacobsson Alexander Berg Ivan Maximov magnus t. borgstrom Solid State Physics Lund University Box 118 S-22100 Lund Sweden

Position controlled nanowire growth is important for nanowire-based optoelectronic components which rely on light emission or light absorption. For solar energy harvesting applications, dense arrays of nanowires are needed; however, a major obstacle to obtaining dense nanowire arrays is seed particle displacement and coalescing during the annealing stage prior to nanowire growth. Here, we explore three different strategies to improve pattern preservation of large-area catalyst particle arrays defined by nanoimprint lithography for nanowire growth. First, we see that heat treating the growth substrate prior to nanoimprint lithography improves pattern preservation. Second, we explore the possibility of improving pattern preservation by fixing the seed particles in place prior to annealing by modifying the growth procedure. And third, we show that a SiNx growth mask can fully prevent seed particle displacement. We show how these strategies allow us to greatly improve the pattern fidelity of grown InP nanowire arrays with dimensions suitable for solar cell applications, ultimately achieving 100% pattern preservation over the sampled area. the generic nature of these strategies is supported through the synthesis of GaAs and GaP nanowires.

关键词： semiconductor nanowire nanoimprint lithography metal-organic vaporphase epitaxial (MOVPE) patterning

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Absorption of light in InP nanowire arrays

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Nano Research 2014年第6期7卷 816-823页

作者： Nicklas Anttu Alireza Abrand Damir Asoli magnus Heurlin Ingvar Aberg Lars Samuelson magnus borgstrom Division of Solid State Physics and the Nanometer Structure Consortium at Lund University (nmC@LU) Lund University Box 118 Lund 22100 Sweden Sol Voltaics AB Ideon Science Park Scheelevagen 17 Lund 22370 Sweden

An understanding of the absorption of light is essential for efficient photovoltaic and photodetection applications with III-V nanowire arrays. Here, we correlate experiments with modeling and verify experimentally the predicted absorption of light in InP nanowire arrays for varying nanowire diameter and length. We find that 2,000 nm long nanowires in a pitch of 400 nm can absorb 94% of the incident light with energy above the band gap and, as a consequence, light which in a simple ray-optics description would be travelling between the nanowires can be efficiently absorbed by the nanowires. Our measurements demonstrate that the absorption for long nanowires is limited by insertion reflection losses when light is coupled from the air top-region into the array. these reflection losses can be reduced by introducing a smaller diameter to the nanowire-part closest to the air top-region. For nanowire arrays with such a nanowire morphology modulation, we find that the absorptance increases monotonously with increasing diameter of the rest of the nanowire.

关键词： indium phosphide semiconductor nanowire absorption of light

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Growth and optical properties of InxGa1-xP nanowires synthesized by selective-area epitaxy

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Nano Research 2017年第2期10卷 672-682页

作者： Alexander Berg Philippe Caroff Naeem Shahid Mark N. Lockrey Xiaoming Yuan magnus t. borgstrom Hark Hoe tan Chennupati Jagadish Solid State Physics and NanoLund Lund University Box 118 SE-221 00 Lund Sweden Department of Electronic Materials Engineering Research School of Physics and Engineering The Australian National University Canberra ACT2601 Australia Australian National Fabrication Facility Research School of Physics and Engineering The Australian National University Canberra ACT 2601 Australia

ternary III-V nanowires （NWs） cover a wide range of wavelengths in the solar spectrum and would greatly benefit from being synthesized as position-controlled arrays for improved vertical yield, reproducibility, and tunable optical absorption. Here, we report on successful selective-area epitaxy of metal-particle-free vertical InxGa1-xP NW arrays using metal-organic vapor phase epitaxy and detail their optical properties. A systematic growth study establishes the range of suitable growth parameters to obtain uniform NW growth over a large array. the optical properties of the NWs were characterized by room-temperature cathodoluminescence spectroscopy. tunability of the emission wavelength from 870 nm to approximately 800 nm was achieved. transmission electron microscopy and energy dispersive X-ray measurements performed on cross- section samples revealed a pure wurtzite crystal structure with very few stacking faults and a slight composition gradient along the NW growth axis.

关键词： nanowire InGaP selective-area epitaxy cathodoluminescence energy-dispersive X-ray spectroscopy

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Large-energy-shift photon upconversion in degenerately doped InP nanowires by direct excitation into the electron gas

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Nano Research 2013年第10期6卷 752-757页

作者： Kilian Mergenthaler Azhar Iqbal Jesper Wallentin Sebastian Lehmann magnus t. borgstrom Lars Samuelson Arkady Yartsev Mats-Erik Pistol Solid State Physics/the Nanometer Structure Consortium Lund University P. O. Box 118 SE-22100 Lund Sweden Division of Chemical Physics Lund University P O. Box 118 SE-22100 Lund Sweden

Realizing photon upconversion in nanostructures is important for many next- generation applications such as biological labelling, infrared detectors and solar cells. In particular nanowires are attractive for optoelectronics because they can easily be electrically contacted. Here we demonstrate photon upconversion with a large energy shift in highly n-doped InP nanowires. Crucially, the mechanism responsible for the upconversion in our system does not rely on multi-photon absorption via intermediate states, thus eliminating the need for high photon fluxes to achieve upconversion. the demonstrated upconversion paves the way for utilizing nanowires--with their inherent flexibility such as electrical contactability and the ability to position individual nanowires--for photon upconversion devices also at low photon fluxes, possibly down to the single photon level in optimised structures.

关键词： nanowires photon upconversion photoluminescence indium phosphide

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Semiconductor nanostructures enabled by aerosol technology

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Frontiers of physics 2014年第3期9卷 398-418页

作者： Martin H. magnusson B. Jonas Ohlsson Mikael t. Bjork Kimberly A. Dick magnus t. borgstrom Knut Deppert Lars Samuelson Solid State Physics Lund University Box 118 SE-22100 Lund Sweden Sol Voltaics AB Ideon Science Park Scheelevagen 17 SE-22370 Lund Sweden QuNano AB Ideon Science Park Scheelevaigen 17 SE-22370 Lund Sweden Center for Analysis and Synthesis Lund University Box 124 SE-22100 Lund Sweden

Aerosol technology provides efficient methods for producing nanoparticles with well-controlled composition and size distribution. this review provides an overview of methods and results obtained by using aerosol technology for producing nanostruetures for a variety of applications in semiconductor physics and device technology. Examples are given from： production of metal and metal alloy particles： semiconductor nanoparticles; semiconductor nanowires, grown both in the aerosol phase and on substrates; physics studies based on individual aerosol-generated devices; and large area deviees based on aerosol particles.

关键词： aerosol nanoparticle nanowire metal-organic vapor phase epitaxy (MOVPE) device physics light emitting diodes (LED) solar cell

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Valence Band Splitting in Wurtzite InP Nanowires Observed by Photoluminescence and Photoluminescence Excitation Spectroscopy

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Nano Research 2011年第2期4卷 159-163页

作者： Gerben L. tuin magnus t. borgstrom Johanna tragardh Martin Ek L. Reine Wallenberg Lars Samuelson Mats-Erik Pistol Solid State Physics/Nanometer Structure Consortium Box 118 Lund University S-221 00 Lund Sweden Polymer ＆ Materials Chemistry/nCHREM Lund University S-22100 Lurid Sweden

We have investigated individual bulk-like wires of wurtzite InP using photoluminescence, photoluminescence excitation spectroscopy and transmission electron microscopy. Using two different methods we find that the top of the valence band is split, as expected theoretically. this splitting of the valence band is peculiar to wurtzite InP and does not occur in zinc blende InP. We find the energy difference between the two bands to be 40 meV.

关键词： wurtzite InP photoluminescence excitation spectroscopy valence band structure

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Study of photocurrent generation in InP nanowire-based p＋-i-n＋ photodetectors

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Nano Research 2014年第4期7卷 544-552页

作者： Vishal Jain Ali Nowzari Jesper Wallentin magnus t. borgstrom Maria E. Messing Damir Asoli Mariusz Graczyk Bemd Witzigmann Federico Capasso Lars Samuelson Hakan Pettersson Solid State Physics and the Nanometer Structure Consortium Lund University Box 118 5E-221 O0 Lund Sweden Laboratory of Mathematics Physics and Electrical Engineering Halmstad University Box 823 SE-301 - 18 Halmstad Sweden Sol Voltaics AB Ideon Science Park Scheelevagen 17 SE-22370 Lund Sweden Department of Computational Electronics and Photonics University ofKassel Wilhelmshoeher Allee 71 D-34121 Kassel Germany School of Engineering and Applied Sciences Harvard University Cambridge Massachusetts 02138 USA

We report on electrical and optical properties of p＋-i-n＋ photodetectors/solar cells based on square millimeter arrays of InP nanowires （NWs） 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 cells with 9.3% efficiency with similar design. the electrical data for all devices display clear rectifying behavior with an ideality factor between 1.8 and 2.5 at 300 K. From spectrally resolved photocurrent measurements, we conclude that the photocurrent generation process depends strongly on the p^-segment length. Without a p＋-segment, photogenerated carriers funneled from the substrate into the NWs contribute strongly to the photocurrent. Adding a p＋-segment decouples the substrate and shifts the depletion region, and collection of photogenerated carriers, to the NWs, in agreement with theoretical modeling. In optimized solar cells, clear spectral signatures of interband transitions in the zinc blende and wurtzite InP layers of the mixed-phase i-segments are observed. Complementary electroluminescence, transmission electron microscopy （tEM）, as well as measurements of the dependence of the photocurrent on angle of incidence and polarization, support our interpretations.

关键词： nanophotonics nanowires infrared (IR) photodetectors solar cells

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Assessing progression of keratoconus: novel tomographic determinants

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Eye and Vision 2016年第1期3卷 49-57页

作者： Joshua K.Duncan Michael W.Belin Mark borgstrom Department of Ophthalmology&Vision Science University of ArizonaTucsonAZUSA University of Arizona University Information Technology ServicesTucsonAZUSA

Several methods have been described in the literature to both evaluate and document progression in keratoconus,but there is no consistent or clear definition of ectasia *** authors describe how modern corneal tomography,including both anterior and posterior elevation and pachymetric data can be used to screen for ectatic progression,and how software programs such as the Enhanced Reference Surface and the Belin-Ambrosio Enhanced Ectasia Display(BAD)can be employed to detect earlier ***,in order to describe specific quantitative values that can be used as progression determinants,the normal noise measurement of the three parameters(corneal thickness at the thinnest point,anterior and posterior radius of curvature(ARC,PRC)taken from the 3.0 mm optical zone centered on the thinnest point),was *** values were obtained by imaging five normal patients using three different technicians on three separate *** 95%and 80%one-sided confidence intervals for all three parameters were surprisingly small(7.88/4.03μm for corneal thickness,0.024/0.012 mm for ARC,and 0.083/0.042 mm for PRC),suggesting that they may perform well as progression determinants.

关键词： Keratoconus tomography Ectatic disease Progression Amsler-Krumeich Scheimpflug Collagen cross-linking

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