| 1. |
- Zhu, Zhongyunshen, et al.
(författare)
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Performance enhancement of GaSb vertical nanowire p-type MOSFETs on Si by rapid thermal annealing
- 2022
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 33:7
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Tidskriftsartikel (refereegranskat)abstract
- GaSb is considered as an attractive p-type channel material for future III-V metal-oxide-semiconductor (MOS) technologies, but the processing conditions to utilize the full device potential such as low power logic applications and RF applications still need attention. In this work, applying rapid thermal annealing (RTA) to nanoscale GaSb vertical nanowire p-type MOS field-effect transistors, we have improved the average peak transconductance (g m,peak) by 50% among 28 devices and achieved 70 μS μm-1 at V DS = -0.5 V in a device with 200 nm gate length. In addition, a low subthreshold swing down to 144 mV dec-1 as well as an off-current below 5 nA μm-1 which refers to the off-current specification in low-operation-power condition has been obtained. Based on the statistical analysis, the results show a great enhancement in both on- and off-state performance with respect to previous work mainly due to the improved electrostatics and contacts after RTA, leading to a potential in low-power logic applications. We have also examined a short channel device with L g = 80 nm in RTA, which shows an increased g m,peak up to 149 μS μm-1 at V DS = -0.5 V as well as a low on-resistance of 4.7 kΩ•μm. The potential of further enhancement in g m via RTA offers a good alternative to obtain high-performance devices for RF applications which have less stringent requirement for off-state performance. Our results indicate that post-fabrication annealing provides a great option to improve the performance of GaSb-based p-type devices with different structures for various applications.
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| 2. |
- Dick Thelander, Kimberly, et al.
(författare)
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Height-controlled nanowire branches on nanotrees using a polymer mask
- 2007
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 18:3
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Tidskriftsartikel (refereegranskat)abstract
- The production of complex three-dimensional dendritic structures is an important step in the application of semiconductor nanowires. One promising method for achieving this is the sequential seeding of multiple generations of epitaxial nanowires using metal seed particles. However, it is difficult to control and predict the position of second and higher generation nanowires with respect to the first generation. Here we demonstrate a procedure for controlling the position of second-generation epitaxial nanowire branches on vertically aligned nanowire trunks. This method uses a spun-on polymer layer that masks first-generation wires to a specified height, preventing the growth of nanowire branches at lower positions as well as new nanowire growth on the substrate. This method appears not to be dependent on the materials or growth system (in this case MOVPE-grown GaP is demonstrated), and hence is likely to be applicable to a variety of materials systems and growth procedures using metal seed particles.
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| 3. |
- Larsson, Magnus, et al.
(författare)
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Strain mapping in free-standing heterostructured wurtzite InAs/InP nanowires
- 2007
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 18:1
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Tidskriftsartikel (refereegranskat)abstract
- The strain distribution in heterostructured wurtzite InAs/InP nanowires is measured by a peak finding technique using high resolution transmission electron microscopy images. We find that nanowires with a diameter of about 20 nm show a 10 nm strained area over the InAs/InP interface and the rest of the wire has a relaxed lattice structure. The lattice parameters and elastic properties for the wurtzite structure of InAs and InP are calculated and a nanowire interface is simulated using finite element calculations. Both the method and the experimental results are validated using a combination of finite element calculations and image simulations.
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| 4. |
- Lindgren, David, et al.
(författare)
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Study of carrier concentration in single InP nanowires by luminescence and Hall measurements
- 2015
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 26:4
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Tidskriftsartikel (refereegranskat)abstract
- The free electron carrier concentrations in single InP core-shell nanowires are determined by micro-photoluminescence, cathodoluminescence (CL) and Hall effect measurements. The results from luminescence measurements were obtained by solving the Fermi-Dirac integral, as well as by analyzing the peak full width at half maximum (FWHM). Furthermore, the platform used for Hall effect measurements, combined with spot mode CL spectroscopy, is used to determine the carrier concentrations at specific positions along single nanowires. The results obtained via luminescence measurements provide an accurate and rapid feedback technique for the epitaxial development of doping incorporation in nanowires. The technique has been employed on several series of samples in which growth parameters, such as V/III-ratio, temperature and dopant flows, were investigated in an optimization procedure. The correlation between the Hall effect and luminescence measurements for extracting the carrier concentration of different samples were in excellent agreement.
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| 5. |
- Thiagarajan, Kannan, 1981-, et al.
(författare)
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High-field electron transport in semiconducting zigzag carbon nanotubes
- 2012
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Ingår i: Nanotechnology. - Bristol, England : IOP Publishing. - 0957-4484 .- 1361-6528. ; 23:26, s. 265703-265709
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Tidskriftsartikel (refereegranskat)abstract
- Electron transport in semiconducting zigzag carbon nanotubes is studied by solving the Boltzmann transport equation using the single-particle Monte Carlo technique. The electronic band structure is based on a standard nearest-neighbour tight-binding parameterisation, and the phonon spectrum is calculated using a fourth nearest-neighbour force constant model. The electron-phonon scattering probabilities are calculated within a tight-binding formalism. The steady-state drift velocities for the semiconducting zigzag nanotubes (8,0), (10,0), (11,0), (13,0), and (25,0) are computed as functions of electric field strength and temperature, and the results are analysed here. The results show the presence of negative differential resistance at high electric fields for some of the nanotubes. The drift velocity and the low field mobility reach a maximum value of and, respectively, for a (25,0) nanotube.
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| 6. |
- Håkanson, Ulf, et al.
(författare)
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Nano-aperture fabrication for single quantum dot spectroscopy
- 2003
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 14:6, s. 675-679
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Tidskriftsartikel (refereegranskat)abstract
- We present a simple and controllable method for fabricating nano-apertures in a metal film using polystyrene nano-spheres as masks during the metal evaporation. We show how the processing conditions used during deposition of the spheres such as spin velocity, nano-sphere concentration and a reduction of the surface tension interplay and control the distribution of spheres. The fabrication method is ideal for luminescence studies by isolating individual nanometre-sized objects, which is exemplified by photoluminescence spectroscopy of single self-assembled Stranski-Krastanow quantum dots.
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| 7. |
- Abbondanza, Giuseppe, 1991, et al.
(författare)
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Hydride formation and dynamic phase changes during template-assisted Pd electrodeposition
- 2023
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Ingår i: Nanotechnology. - 1361-6528 .- 0957-4484. ; 34:50
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the structural evolution of electrochemically fabricated Pd nanowires in situ by means of grazing-incidence transmission small- and wide-angle x-ray scattering (GTSAXS and GTWAXS), x-ray fluorescence (XRF) and two-dimensional surface optical reflectance (2D-SOR). This shows how electrodeposition and the hydrogen evolution reaction (HER) compete and interact during Pd electrodepositon. During the bottom-up growth of the nanowires, we show that beta-phase Pd hydride is formed. Suspending the electrodeposition then leads to a phase transition from beta-phase Pd hydride to alpha-phase Pd. Additionally, we find that grain coalescence later hinders the incorporation of hydrogen in the Pd unit cell. GTSAXS and 2D-SOR provide complementary information on the volume fraction of the pores occupied by Pd, while XRF was used to monitor the amount of Pd electrodeposited.
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| 8. |
- Aïssa, B., et al.
(författare)
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Functionalized single-walled carbon-nanotube-blended P3HT-based high performance memory behavior thin-film transistor devices
- 2020
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 31:7
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Tidskriftsartikel (refereegranskat)abstract
- We report on the fabrication and transport properties of single-walled carbon nanotubes (SWCNT) blended with P3HT (poly 3-hexyl thiophene-2, 5-diyl). The composite is used as a hybrid organic active channel transistor. The performances of the fabricated devices were investigated as a function of the SWCNTs' loads in the composite, and their response evaluated under white light illumination. Our results show that for SWCNT loads ≤1.5 wt%, all the devices behave as p-type transistors, exhibiting excellent performance, with an I on /I off ratio of 104 and a maximum on-state current (I on) exceeding 80 μA. Moreover, compared with pristine transistors with a P3HT channel, the Hall mobility of these hybrid TFTs was found to increase by more than one order of magnitude, i.e. increasing from 0.062 to 1.54 cm2 V-1 s-1. Finally, under light illumination, the transfer characteristics (i.e. I DS as a function of V GS) were found to systematically undergo a typical shift together with a fully-reversible memory behavior. A fundamental understanding of this work can assist in providing new routes for the development of reliable efficient hybrid organic-based optoelectronic devices.
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| 9. |
- Anttu, Nicklas, et al.
(författare)
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Absorption and transmission of light in III-V nanowire arrays for tandem solar cell applications
- 2017
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 28:20
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Tidskriftsartikel (refereegranskat)abstract
- III-V semiconductor nanowires are a platform for next-generation photovoltaics. An interesting research direction is to embed a nanowire array in a transparent polymer, either to act as a stand-alone flexible solar cell, or to be stacked on top of a conventional Si bottom cell to create a tandem structure. To optimize the tandem cell performance, high energy photons should be absorbed in the nanowires whereas low energy photons should be transmitted to and absorbed in the Si cell. Here, through optical measurements on 1.95 eV bandgap GaInP nanowire arrays embedded in a polymer membrane, we identify two mechanisms that could be detrimental for the performance of the tandem cell. First, the Au particles used in the nanowire synthesis can absorb >50% of the low-energy photons, leading to a <40% transmittance, even though the Au particles cover <15% of the surface area. The removal of the Au particles can recover the transmission of low energy photons to >80%. Second, after the removal of the Au particles, a 40% reflectance peak shows up due to resonant back-scattering of light from in-plane waveguide modes. To avoid the excitation of these optical modes in the nanowire array, we propose to limit the pitch of the nanowire array.
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| 10. |
- Borg, Mattias, et al.
(författare)
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Facet-selective group-III incorporation in InGaAs template assisted selective epitaxy
- 2019
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 30:8
-
Tidskriftsartikel (refereegranskat)abstract
- InGaAs is a potential candidate for Si replacement in upcoming advanced technological nodes because of its excellent electron transport properties and relatively low interface defect density in dielectric gate stacks. Therefore, integrating InGaAs devices with the established Si platforms is highly important. Using template-assisted selective epitaxy (TASE), InGaAs nanowires can be monolithically integrated with high crystal quality, although the mechanisms of group III incorporation in this ternary material have not been thoroughly investigated. Here we present a detailed study of the compositional variations of InGaAs nanostructures epitaxially grown on Si(111) and Silicon-on-insulator substrates by TASE. We present a combination of XRD data and detailed EELS maps and find that the final Ga/In chemical composition depends strongly on both growth parameters and the growth facet type, leading to complex compositional sub-structures throughout the crystals. We can further conclude that the composition is governed by the facet-dependent chemical reaction rates at low temperature and low V/III ratio, while at higher temperature and V/III ratio, the incorporation is transport limited. In this case we see indications that the transport is a competition between Knudsen flow and surface diffusion.
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| 11. |
- Buchanan, Claire, et al.
(författare)
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C-amidation of substituted β 3oligoamides yields novel supramolecular assembly motif
- 2022
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 33:2
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Tidskriftsartikel (refereegranskat)abstract
- N-acylated substituted β 3 oligoamides are known to form unique supramolecular nanorods based on a 3-point hydrogen bond self-assembly motif. This motif is an intermolecular extension of the hydrogen bonding network that stabilizes the 14-helix secondary structure unique to β 3 oligoamides. Acetylation of the N-terminus of the molecule provides the necessary third hydrogen bond pair of the motif. Here, the possibility of introducing the third hydrogen bond pair via amidation of the C terminus is investigated. While similar in purpose, this modification introduces a chemically distinct new self-assembly motif, also removing the bulky carboxyl group that does not fold into the 14 helix positioning instead as a side chain. Three substituted β 3 oligoamide variants with the base sequence LIA (where the letters denote β 3 residues with side chains analogous to α amino acids) were compared: N-acylated Ac-β 3[LIA] as a reference, C-amidated β 3[LIA]-CONH2, and β 3[LIA] with free unmodified N and C termini as a negative control. The three variants were dissolved in water to promote self-assembly. The self-assembly was characterised using mid- and far-infrared spectroscopy, small angle x-ray scattering (SAXS) and atomic force microscopy (AFM). IR measurements confirmed that all three samples were in a similar conformation, consistent with pseudo 14-helical secondary structures. Far-infrared spectroscopy measurements of β 3[LIA]-CONH2 showed distinct peaks consistent with highly organised skeletal modes, i.e. regular supramolecular assembly, that was largely absent from the other two oligoamides. Modelling of SAXS data is consistent with elliptical cylinder structures resulting from nanorod bundling for both β 3[LIA]-CONH2 and Ac-β 3[LIA], but not in the unmodified sample. Consistently, AFM imaging showed large nanorod bundling structures in β 3[LIA]-CONH2, varied bundling structures in Ac-β 3[LIA], and only aggregation in β 3[LIA]. Amidation showed much more organised and robust assembly compared to acetylation, providing a new, easy to synthesize self-assembly motif for helical nanorod assembly that is similar but distinct to N-acylation
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| 12. |
- Böckle, R., et al.
(författare)
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Ge quantum wire memristor
- 2020
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 31:44
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Tidskriftsartikel (refereegranskat)abstract
- Despite being known of for decades, the actual realization of memory devices based on the memristive effect is progressing slowly, due to processing requirements and the need for exotic materials which are not compatible with today's complementary-metal-oxide-semiconductor (CMOS) technology. Here, we report an experimental study on a Ge quantum wire device featuring distinct signatures of memristive behavior favorable for integration in CMOS platform technology. Embedding the quasi-1D Ge quantum wire into an electrostatically modulated back-gated field-effect transistor, we demonstrate that individual current transport channels can be addressed directly by controlling the surface trap assisted electrostatic gating. The resulting quantization of the current represents the ultimate limit of memristors with practically zero off-state current and low footprint. In addition, the proposed device has the advantage of non-destructive successive reading cycles capability. Importantly, our findings provide a framework towards fully CMOS compatible ultra-scaled Ge based memristors.
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| 13. |
- Chalangar, Ebrahim, 1984-, et al.
(författare)
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Influence of morphology on electrical and optical properties of graphene/Al-doped ZnO-nanorod composites
- 2018
-
Ingår i: Nanotechnology. - Bristol : Institute of Physics Publishing (IOPP). - 0957-4484 .- 1361-6528. ; 29:41
-
Tidskriftsartikel (refereegranskat)abstract
- The development of future 3D-printed electronics relies on the access to highly conductive inexpensive materials that are printable at low temperatures (<100 C). The implementation of available materials for these applications are, however, still limited by issues related to cost and printing quality. Here, we report on the simple hydrothermal growth of novel nanocomposites that are well suited for conductive printing applications. The nanocomposites comprise highly Al-doped ZnO nanorods grown on graphene nanoplatelets (GNPs). The ZnO nanorods play the two major roles of (i) preventing GNPs from agglomerating and (ii) promoting electrical conduction paths between the graphene platelets. The effect of two different ZnO-nanorod morphologies with varying Al-doping concentration on the nanocomposite conductivity and the graphenedispersity are investigated. Time-dependent absorption, photoluminescence and photoconductivity measurements show that growth in high pH solutions promotes a better graphene dispersity, higher doping levels and enhanced bonding between the graphene and the ZnO nanorods. Growth in low pH solutions yields samples characterized by a higher conductivity and a reduced number of surface defects. These samples also exhibit a large persistent photoconductivity attributed to an effective charge separation and transfer from the nanorods to the graphene platelets. Our findings can be used to tailor the conductivity of novel printable composites, or for fabrication of large volumes of inexpensive porous conjugated graphene-semiconductor composites. © 2018 IOP Publishing Ltd.
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| 14. |
- Chalangar, Ebrahim, PhD student, 1984-, et al.
(författare)
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Nanopatterned rGO/ZnO : Al seed layer for vertical growth of single ZnO nanorods
- 2023
-
Ingår i: Nanotechnology. - Bristol : Institute of Physics Publishing (IOPP). - 0957-4484 .- 1361-6528. ; 34:25, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we demonstrate a novel low-cost template-assisted route to synthesize vertical ZnO nanorod arrays on Si (100). The nanorods were grown on a patterned double seed layer comprised of reduced graphene oxide (rGO) and Al-doped ZnO nanoparticles. The seed layer was fabricated by spray-coating the substrate with graphene and then dip-coating it into a Al-doped ZnO sol-gel solution. The growth template was fabricated from a double-layer resist, spin-coated on top of the rGO/ZnO:Al seed layer, and patterned by colloidal lithography. The results show a successful chemical bath deposition of vertically aligned ZnO nanorods with controllable diameter and density in the nanoholes in the patterned resist mask. Our novel method can presumably be used to fabricate electronic devices on virtually any smooth substrate with a thermal budget of 1 min at 300 °C with the seed layer acting as a conductive strain-relieving back contact. The top contact can simply be made by depositing a suitable transparent conductive oxide or metal, depending on the specific application. © 2023 The Author(s). Published by IOP Publishing Ltd.
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| 15. |
- Chayanun, Lert, et al.
(författare)
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Spectrally resolved x-ray beam induced current in a single InGaP nanowire
- 2018
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 29:45
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate x-ray absorption fine structure spectroscopy (XAFS) detected by x-ray beam induced current (XBIC) in single n + -i-n + doped nanowire devices. Spatial scans with the 65 nm diameter beam show a peak of the XBIC signal in the middle segment of the nanowire. The XBIC and the x-ray fluorescence signals were detected simultaneously as a function of the excitation energy near the Ga K absorption edge at 10.37 keV. The spectra show similar oscillations around the edge, which shows that the XBIC is limited by the primary absorption. Our results reveal the feasibility of the XBIC detection mode for the XAFS investigation in nanostructured devices.
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| 16. |
- Chen, Yang, et al.
(författare)
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Optical far-field extinction of a single GaAs nanowire towards in situ size control of aerotaxy nanowire growth
- 2020
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 31:13
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Tidskriftsartikel (refereegranskat)abstract
- A substrate-free approach of semiconductor nanowire growth has been achieved by the aerotaxy technique previously. In this work, we propose an in situ method to monitor the size of nanowires through non-destructive optical-extinction measurements. Our work aims to build a theoretical look-up database of extinction spectra for a single nanowire of varying dimensions. We describe the origin of possible peaks in the spectra, for example due to nanowire-length dependent Fabry-Perot resonances and nanowire-diameter dependent TM and TE mode resonances. Furthermore, we show that the Au catalyst on top of the nanowire can be ignored in the simulations when the volume of the nanowire is an order of magnitude larger than that of the Au catalyst and the diameter is small compared to the incident wavelength. For the calculation of the extinction spectra, we use the finite element method, the discrete dipole approximation and the Mie theory. To compare with experimental measurements of randomly oriented nanowires, we perform an averaging over nanowire orientation for the modeled results. However, in the experiments, nanowires are accumulating on the quartz window of the measurement setup, which leads to increasing uncertainty in the comparison with the experimental extinction spectra. This uncertainty can be eliminated by considering both a sparse and a dense collection of nanowires on the quartz window in the optical simulations. Finally, we create a database of extinction spectra for a GaAs nanowire of varying diameters and lengths. This database can be used to estimate the diameter and the length of the nanowires by comparing the position of a peak and the peak-to-shoulder difference in the extinction spectrum. Possible tapering of nanowires can be monitored through the appearance of an additional peak at a wavelength of 700-800 nm.
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| 17. |
- Chen, Yang, et al.
(författare)
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Optimized efficiency in InP nanowire solar cells with accurate 1D analysis
- 2018
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 29:4
-
Tidskriftsartikel (refereegranskat)abstract
- Semiconductor nanowire arrays are a promising candidate for next generation solar cells due to enhanced absorption and reduced material consumption. However, to optimize their performance, time consuming three-dimensional (3D) opto-electronics modeling is usually performed. Here, we develop an accurate one-dimensional (1D) modeling method for the analysis. The 1D modeling is about 400 times faster than 3D modeling and allows direct application of concepts from planar pn-junctions on the analysis of nanowire solar cells. We show that the superposition principle can break down in InP nanowires due to strong surface recombination in the depletion region, giving rise to an IV-behavior similar to that with low shunt resistance. Importantly, we find that the open-circuit voltage of nanowire solar cells is typically limited by contact leakage. Therefore, to increase the efficiency, we have investigated the effect of high-bandgap GaP carrier-selective contact segments at the top and bottom of the InP nanowire and we find that GaP contact segments improve the solar cell efficiency. Next, we discuss the merit of p-i-n and p-n junction concepts in nanowire solar cells. With GaP carrier selective top and bottom contact segments in the InP nanowire array, we find that a p-n junction design is superior to a p-i-n junction design. We predict a best efficiency of 25% for a surface recombination velocity of 4500 cm s-1, corresponding to a non-radiative lifetime of 1 ns in p-n junction cells. The developed 1D model can be used for general modeling of axial p-n and p-i-n junctions in semiconductor nanowires. This includes also LED applications and we expect faster progress in device modeling using our method.
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| 18. |
- Corrêa, Gregório B., et al.
(författare)
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Raman characterization of single-crystalline Ga0.96Mn0.04As:Zn nanowires realized by ion-implantation
- 2019
-
Ingår i: Nanotechnology. - Bristol : IOP Publishing. - 0957-4484 .- 1361-6528. ; 30:33
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 19. |
- Dagyte, Vilgaile, et al.
(författare)
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Growth kinetics of GaxIn(1−x)P nanowires using triethylgallium as Ga precursor
- 2018
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 29:39
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Tidskriftsartikel (refereegranskat)abstract
- GaxIn(1−x)P nanowire arrays are promising for various optoelectronic applications with a tunable band-gap over a wide range. In particular, they are well suited as the top cell in tandem junction solar cell devices. So far, most GaxIn(1−x)P nanowires have been synthesized by the use of trimethylgallium (TMGa). However, particle assisted nanowire growth in metal organic vapor phase epitaxy is typically carried out at relatively low temperatures, where TMGa is not fully pyrolysed. In this work, we developed the growth of GaxIn(1−x)P nanowires using triethylgallium (TEGa) as the Ga precursor, which reduced Ga precursor consumption by about five times compared to TMGa due to the lower homogeneous pyrolysis temperature of TEGa. The versatility of TEGa is shown by synthesis of high yield GaxIn(1−x)P nanowire arrays, with a material composition tunable by the group III input flows, as verified by x-ray diffraction measurements and photoluminescence characterization. The growth dynamics of GaxIn(1−x)P nanowires was assessed by varying the input growth precursor molar fractions and growth temperature, using hydrogen-chloride as in situ etchant. We observed a complex interplay between the precursors. First, trimethylindium (TMIn) inhibits Ga incorporation into the nanowires, resulting in higher In composition in the grown nanowires than in the vapor. Second, the growth rate increases with temperature, indicating a kinetically limited growth, which from nanowire effective binary volume growth rates of InP and GaP can be attributed to the synthesis of GaP in GaxIn(1−x)P. We observed that phosphine has a strong effect on the nanowire growth rate with behavior expected for a unimolecular Langmuir–Hinshelwood mechanism of pyrolysis on a catalytic surface. However, growth rates increase strongly with both TEGa and TMIn precursors as well, indicating the complexity of vapor–liquid–solid growth for ternary materials. One precursor can affect the decomposition of another, and each precursor can affect the wetting properties and catalytic activity of the metal particle.
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| 20. |
- Dagytė, Vilgailė, et al.
(författare)
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Modal analysis of resonant and non-resonant optical response in semiconductor nanowire arrays
- 2019
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 30:2
-
Tidskriftsartikel (refereegranskat)abstract
- Nanowire array solar cells have reached efficiencies where it becomes feasible to talk about creating tandem solar cells in order to achieve even higher efficiencies. An example of such a tandem solar cell could be a nanowire array embedded in a membrane and integrated on top of a Si bottom cell. Such a system, however, requires understanding and control of its interaction with light, especially to make sure that the low energy photons are transmitted to the bottom cell. The dependence of the optical response of a nanowire array on the nanowire length, diameter, array pitch, materials surrounding the nanowires, and absorption coefficient of the nanowire material is very strong and possibly resonant, indicating the complexity of the optical response. In this work, we use an eigenmode-based analysis to reveal underlying physics that gives rise to observed resonant and non-resonant behavior. First, we show that an effective refractive index can be defined at long wavelengths, where only a single mode propagates. Second, we analyze the origin of the resonant reflection when the next optical mode becomes propagating and can be 'trapped' in the array and interact with the fundamental mode. Additionally, we define two simple boundaries for the wavelength range of the resonant response: the resonances can only occur if there is more than 1 propagating mode in the array, and they disappear if the 1st diffracted order is propagating in the top or bottom material. Such resonance effects could be detrimental for tandem solar cells. We thus provide recommendations for tuning the geometry of the array and the nanowire materials in order to push the resonant regime to the absorbing regime of the nanowire, where absorption in the nanowires dampens the resonances. Finally, this work demonstrates the strength of an eigenmode-based analysis of the optical response of periodic nanostructures in terms of simplifying the analysis of a complex system.
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| 21. |
- Dagyte, Vilgaile, et al.
(författare)
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Time-resolved photoluminescence characterization of GaAs nanowire arrays on native substrate
- 2017
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 28:50
-
Tidskriftsartikel (refereegranskat)abstract
- Time-resolved photoluminescence (TRPL) measurements of nanowires (NWs) are often carried out on broken-off NWs in order to avoid the ensemble effects as well as substrate contribution. However, the development of NW-array solar cells could benefit from non-destructive optical characterization to allow faster feedback and further device processing. With this work, we show that different NW array and substrate spectral behaviors with delay time and excitation power can be used to determine which part of the sample dominates the detected spectrum. Here, we evaluate TRPL characterization of dense periodic as-grown GaAs NW arrays on a p-type GaAs substrate, including a sample with uncapped GaAs NWs and several samples passivated with AlGaAs radial shell of varied composition and thickness. We observe a strong spectral overlap of substrate and NW signals and find that the NWs can absorb part of the substrate luminescence signal, thus resulting in a modified substrate signal. The level of absorption depends on the NW-array geometry, making a deconvolution of the NW signal very difficult. By studying TRPL of substrate-only and as-grown NWs at 770 and 400 nm excitation wavelengths, we find a difference in spectral behavior with delay time and excitation power that can be used to assess whether the signal is dominated by the NWs. We find that the NW signal dominates with 400 nm excitation wavelength, where we observe two different types of excitation power dependence for the NWs capped with high and low Al composition shells. Finally, from the excitation power dependence of the peak TRPL signal, we extract an estimate of background carrier concentration in the NWs.
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| 22. |
- Devi, Chandni, et al.
(författare)
-
Electrical transport properties of InAs nanowires synthesized by a solvothermal method
- 2020
-
Ingår i: Nanotechnology. - Bristol : Institute of Physics Publishing (IOPP). - 0957-4484 .- 1361-6528. ; 31:23
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 23. |
- Dorsch, S., et al.
(författare)
-
Side-gated, enhancement mode, InAs nanowire double quantum dot devices-toward controlling transverse electric fields in spin-transport measurements
- 2019
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 30:14
-
Tidskriftsartikel (refereegranskat)abstract
- A double quantum dot system with a definitive transverse electric field in the plane of the sample is defined by combining a facile side-gating technique with enhancement mode InAs nanowires. Positive bias on the plunger gates enhance quantum dot segments along the nanowire, negative bias on barrier gates deplete regions, and situating gates biased at opposite polarities on opposing sides of the nanowire allows an electric field to be engineered. With sufficiently biased barrier regions stable bias triangle features are observed in the weak interdot coupling regime. The singlet-triplet energy splitting Δ ST in Pauli spin-blockaded features is studied as a function of an external magnetic field applied perpendicular to the sample plane. We interpret an apparent absence of mixing between singlet and triplet states as an indication that the spin-orbit field is oriented out of the sample plane due to the induced electric field. Finally, we discuss the potential of combining advanced gating architectures with enhancement mode nanowires to control the orientation of the spin-orbit field-a prospect that could enable multiple, nanowire-based spin-qubits to be operated on a single chip with a fixed-angle external magnetic field applied.
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| 24. |
- Ek, Martin, et al.
(författare)
-
Compositional analysis of oxide-embedded III-V nanostructures
- 2022
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 33:37
-
Tidskriftsartikel (refereegranskat)abstract
- Nanowire growth enables creation of embedded heterostructures, where one material is completely surrounded by another. Through materials-selective post-growth oxidation it is also possible to combine amorphous oxides and crystalline, e.g. III-V materials. Such oxide-embedded structures pose a challenge for compositional characterization through transmission electron microscopy since the materials will overlap in projection. Furthermore, materials electrically isolated by an embedding oxide are more sensitive to electron beam-induced alterations. Methods that can directly isolate the embedded material, preferably at reduced electron doses, will be required in this situation. Here, we analyse the performance of two such techniques-local lattice parameter measurements from high resolution micrographs and bulk plasmon energy measurements from electron energy loss spectra-by applying them to analyse InP-AlInP segments embedded in amorphous aluminium oxide. We demonstrate the complementarity of the two methods, which show an overall excellent agreement. However, in regions with residual strain, which we analyse through molecular dynamics simulations, the two techniques diverge from the true value in opposite directions.
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| 25. |
- Ek, M., et al.
(författare)
-
Electron channelling : challenges and opportunities for compositional analysis of nanowires by TEM
- 2020
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 31:36
-
Tidskriftsartikel (refereegranskat)abstract
- Energy dispersive x-ray spectroscopy in a transmission electron microscope is often the first method employed to characterize the composition of nanowires. Ideally, it should be accurate and sensitive down to fractions of an atomic percent, and quantification results are often reported as such. However, one can often get substantial errors in accuracy even though the precision is high: for nanowires it is common for the quantified V/III atomic ratios to differ noticeably from 1. Here we analyse the origin of this systematic error in accuracy for quantification of the composition of III-V nanowires. By varying the electron illumination direction, we find electron channelling to be the primary cause, being responsible for errors in quantified V/III atomic ratio of 50%. Knowing the source of the systematic errors is required for applying appropriate corrections. Lastly, we show how channelling effects can provide information on the crystallographic position of dopants.
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| 26. |
- Fast, Jonatan, et al.
(författare)
-
Hot-carrier separation in heterostructure nanowires observed by electron-beam induced current
- 2020
-
Ingår i: Nanotechnology. - : IOP Publishing. - 1361-6528 .- 0957-4484. ; 31:39
-
Tidskriftsartikel (refereegranskat)abstract
- The separation of hot carriers in semiconductors is of interest for applications such asthermovoltaic photodetection and third-generation photovoltaics. Semiconductor nanowiresoffer several potential advantages for effective hot-carrier separation such as: a high degree ofcontrol and flexibility in heterostructure-based band engineering, increased hot-carriertemperatures compared to bulk, and a geometry well suited for local control of light absorption.Indeed, InAs nanowires with a short InP energy barrier have been observed to produce electricpower under global illumination, with an open-circuit voltage exceeding the Shockley-Queisserlimit. To understand this behaviour in more detail, it is necessary to establish control over theprecise location of electron-hole pair-generation in the nanowire. In this work we performelectron-beam induced current measurements with high spatial resolution, and demonstrate therole of the InP barrier in extracting energetic electrons.We interprete the results in terms ofhot-carrier separation, and extract estimates of the hot carriers’ mean free path.
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| 27. |
- Fritz, Fabian, et al.
(författare)
-
Nanoscale X-ray investigation of magnetic metallofullerene peapods
- 2017
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 28:43
-
Tidskriftsartikel (refereegranskat)abstract
- Endohedral lanthanide ions packed inside carbon nanotubes (CNTs) in a one-dimensional assembly have been studied with a combination of high resolution transmission electron microscopy (HRTEM), scanning transmission X-ray microscopy (STXM), and X-ray magnetic circular dichroism (XMCD). By correlating HRTEM and STXM images we show that structures down to 30 nm are resolved with chemical contrast and record X-ray absorption spectra from endohedral lanthanide ions embedded in individual nanoscale CNT bundles. XMCD measurements of an Er3N@C80 bulk sample and a macroscopic assembly of filled CNTs indicates that the magnetic properties of the endohedral Er3+ ions are unchanged when encapsulated in CNTs. This study demonstrates the feasibility of local magnetic X-ray characterization of low concentrations of lanthanide ions embedded in molecular nanostructures.
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| 28. |
- Ghasemi, Masoomeh, et al.
(författare)
-
Assembling your nanowire : An overview of composition tuning in ternary III-V nanowires
- 2021
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 32:7
-
Forskningsöversikt (refereegranskat)abstract
- The ability to grow defect-free nanowires in lattice-mismatched material systems and to design their properties has made them ideal candidates for applications in fields as diverse as nanophotonics, nanoelectronics and medicine. After studying nanostructures consisting of elemental and binary compound semiconductors, scientists turned their attention to more complex systems - ternary nanowires. Composition control is key in these nanostructures since it enables bandgap engineering. The use of different combinations of compounds and different growth methods has resulted in numerous investigations. The aim of this review is to present a survey of the material systems studied to date, and to give a brief overview of the issues tackled and the progress achieved in nanowire composition tuning. We focus on ternary III x III1-x V nanowires (AlGaAs, AlGaP, AlInP, InGaAs, GaInP and InGaSb) and IIIV x V1-x nanowires (InAsP, InAsSb, InPSb, GaAsP, GaAsSb and GaSbP).
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| 29. |
- Gluschke, J. G., et al.
(författare)
-
Achieving short high-quality gate-all-around structures for horizontal nanowire field-effect transistors
- 2018
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 30:6
-
Tidskriftsartikel (refereegranskat)abstract
- We introduce a fabrication method for gate-all-around nanowire field-effect transistors. Single nanowires were aligned perpendicular to underlying bottom gates using a resist-trench alignment technique. Top gates were then defined aligned to the bottom gates to form gate-all-around structures. This approach overcomes significant limitations in minimal obtainable gate length and gate-length control in previous horizontal wrap-gated nanowire transistors that arise because the gate is defined by wet-etching. In the method presented here gate-length control is limited by the resolution of the electron-beam-lithography process. We demonstrate the versatility of our approach by fabricating a device with an independent bottom gate, top gate, and gate-all-around structure as well as a device with three independent gate-all-around structures with 300, 200, and 150 nm gate length. Our method enables us to achieve subthreshold swings as low as 38 mV dec-1 at 77 K for a 150 nm gate length.
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| 30. |
- Gómez, Víctor J., et al.
(författare)
-
Wafer-scale nanofabrication of sub-100 nm arrays by deep-UV displacement Talbot lithography
- 2020
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 31:29
-
Tidskriftsartikel (refereegranskat)abstract
- In this manuscript, we demonstrate the potential of replacing the standard bottom anti-reflective coating (BARC) with a polymethylglutarimide (PMGI) layer for wafer-scale nanofabrication by means of deep-UV displacement talbot lithography (DTL). PMGI is functioning as a developable non-UV sensitive bottom anti-reflective coating (DBARC). After introducing the fabrication process using a standard BARC-based coating and the novel PMGI-based one, the DTL nanopatterning capabilities for both coatings are compared by means of the fabrication of etched nanoholes in a dielectric layer and metal nanodots made by lift-off. Improvement of DTL capabilities are attributed to a reduction of process complexity by avoiding the use of O2 plasma etching of the BARC layer. We show the capacity of this approach to produce nanoholes or nanodots with diameters ranging from 95 to 200 nm at a wafer-scale using only one mask and a proper exposing dose. The minimum diameter of the nanoholes is reduced from 118 to 95 nm when using the PMGI-based coating instead of the BARC-based one. The possibilities opened by the PMGI-based coating are illustrated by the successful fabrication of an array of nanoholes with sub-100 nm diameter for GaAs nanowire growth on a 2″ GaAs wafer, a 2″ nanoimprint lithography (NIL) master stamp, and an array of Au nanodots made by lift-off on a 4″ silica wafer. Therefore, DTL possess the potential for wafer-scale manufacturing of nano-engineered materials.
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| 31. |
- Gustafsson, Anders, et al.
(författare)
-
Cathodoluminescence investigations of dark-line defects in platelet-based InGaN nano-LED structures
- 2024
-
Ingår i: Nanotechnology. - : IOP Publishing Ltd. - 0957-4484 .- 1361-6528. ; 35:25
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated the optical properties of heterostructured InGaN platelets aiming at red emission, intended for use as nano-scaled light-emitting diodes. The focus is on the presence of non-radiative emission in the form of dark line defects. We have performed the study using hyperspectral cathodoluminescence imaging. The platelets were grown on a template consisting of InGaN pyramids, flattened by chemical mechanical polishing. These templates are defect free, whereas the dark line defects are introduced in the lower barrier and tend to propagate through all the subsequent layers, as revealed by the imaging of different layers in the structure. We conclude that the dark line defects are caused by stacking mismatch boundaries introduced by multiple seeding and step bunching at the edges of the as-polished, dome shaped templates. To avoid these defects, we suggest that the starting material must be flat rather than dome shaped.
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| 32. |
- Gustafsson, Anders, et al.
(författare)
-
Cathodoluminescence visualisation of local thickness variations of GaAs/AlGaAs quantum-well tubes on nanowires
- 2020
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 31:42
-
Tidskriftsartikel (refereegranskat)abstract
- We present spatially and spectrally resolved emission from nanowires with a thin radial layer of GaAs embedded in AlGaAs barriers, grown radially around taper-free GaAs cores. The GaAs layers are thin enough to show quantization, and are quantum wells. Due to their shape, they are referred to as quantum well tubes (QWTs). We have investigated three different nominal QWT thicknesses: 1.5, 2.0, and 6.0 nm. They all show average emission spectra from the QWT with an energy spread corresponding to a thickness variation of 30%. We observe no thickness gradient along the length of the nanowires. Individual NWs show a number of peaks, corresponding to different QW thicknesses. Apart from the thinnest QWT, the integrated emission from the QWTs shows homogeneous emission intensity along the NW. The thinnest QWTs show patchy emission patterns due to the incomplete coverage of the QWT. We observe a few NWs with larger diameters. The QWTs in these NWs show spatially resolved variations across the NW. An increase in the local thickness of the QWT at the corners blocks the diffusion of carriers from facet to facet, thereby enabling us to visualise the thickness variations of the radial quantum wells.
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| 33. |
- Hallberg, Robert T., et al.
(författare)
-
Nanowire morphology and particle phase control by tuning the in concentration of the foreign metal nanoparticle
- 2018
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 30:5
-
Tidskriftsartikel (refereegranskat)abstract
- Controllable particle assisted growth (PAG) of III-V nanowires is today almost exclusively done with Au, Ga or In nanoparticles, whereas other metals often yield nanowires with uncontrolled growth directions. To improve the control of the initial growth direction in PAG, independent of choice of metal, we propose to initiate nanowire growth from a group-III-rich foreign metal particle. For III-V nanowire growth, the group III concentration of the particle can be made to increase or decrease with the relative supply of group III and group V material, which can be used to promote the liquid phase that is necessary for vapor-liquid-solid growth. In this paper, 30 nm Pd nanoparticles are used to develop growth conditions for In-rich PAG of InAs nanowires. The particle size evolution for different growth times and V/III ratios is correlated with changes in nanowire density and morphology. In addition, we demonstrate In-rich Co, Pd, Pt and Rh nanoparticles and optimized In-rich PAG from Au and Pd seeds. The Au and Pd seeded nanowires are remarkably similar and by tuning the particle composition we trigger a morphological change. The vertical nanowire morphology is associated with In-rich nanoparticles that contain a liquid phase. The curly nanowire morphology, with random growth directions have an In concentration less than or equal to that of the most In rich compound of the seed metal-In system.
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| 34. |
- Hussain, Laiq, et al.
(författare)
-
Defect-induced infrared electroluminescence from radial GaInP/AlGaInP quantum well nanowire array light- emitting diodes
- 2017
-
Ingår i: Nanotechnology. - Bristol : IOP Publishing. - 0957-4484 .- 1361-6528. ; 28:48
-
Tidskriftsartikel (refereegranskat)abstract
- Radial GaInP/AlGaInP nanowire array light-emitting diodes (LEDs) are promising candidates for novel high-efficiency solid state lighting due to their potentially large strain-free active emission volumes compared to planar LEDs. Moreover, by proper tuning of the diameter of the nanowires, the fraction of emitted light extracted can be significantly enhanced compared to that of planar LEDs. Reports so far on radial growth of nanowire LED structures, however, still point to significant challenges related to obtaining defect-free radial heterostructures. In this work, we present evidence of optically active growth-induced defects in a fairly broad energy range in vertically processed radial GaInP/AlGaInP quantum well nanowire array LEDs using a variety of complementary experimental techniques. In particular, we demonstrate strong infrared electroluminescence in a spectral range centred around 1 eV (1.2 μm) in addition to the expected red light emission from the quantum well. Spatially resolved cathodoluminescence studies reveal a patchy red light emission with clear spectral features along the NWs, most likely induced by variations in QW thickness, composition and barriers. Dark areas are attributed to infrared emission generated by competing defect-assisted radiative transitions, or to trapping mechanisms involving non-radiative recombination processes. Possible origins of the defects are discussed.
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| 35. |
- Jafari Jam, R., et al.
(författare)
-
Embedded sacrificial AlAs segments in GaAs nanowires for substrate reuse
- 2020
-
Ingår i: Nanotechnology. - Bristol : Institute of Physics Publishing (IOPP). - 0957-4484 .- 1361-6528. ; 31:20
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the use of a sacrificial AlAs segment to enable substrate reuse for nanowire synthesis. A silicon nitride template was deposited on a p-type GaAs substrate. Then a pattern was transferred to the substrate by nanoimprint lithography and reactive ion etching. Thermal evaporation was used to define Au seed particles. Metalorganic vapour phase epitaxy was used to grow AlAs-GaAs NWs in the vapour-liquid-solid growth mode. The yield of synthesised nanowires, compared to the number expected from the patterned template, was more than 80%. After growth, the nanowires were embedded in a polymer and mechanically removed from the parent substrate. The parent substrate was then immersed in an HCl:H2O (1:1) mixture to dissolve the remaining stub of the sacrificial AlAs segment. The pattern fidelity was preserved after peeling off the nanowires and cleaning, and the semiconductor surface was flat and ready for reuse. Au seed particles were then deposited on the substrate by use of pulse electrodeposition, which was selective to the openings in the growth template, and then nanowires were regrown. The yield of regrowth was less optimal compared to the first growth but the pattern was preserved. Our results show a promising approach to reduce the final cost of III-V nanowire based solar cells. © 2020 The Author(s). Published by IOP Publishing Ltd.
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| 36. |
- Jain, Vishal, et al.
(författare)
-
Bias-dependent spectral tuning in InP nanowire-based photodetectors
- 2017
-
Ingår i: Nanotechnology. - Bristol : IOP Publishing. - 0957-4484 .- 1361-6528. ; 28:11
-
Tidskriftsartikel (refereegranskat)abstract
- 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/SiO x wrap-gate geometry. Finally, we discuss possible reasons for the observed low saturation current at large forward biases.
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| 37. |
- Jeddi Abdarloo, Hossein, Doktorand, 1992-, et al.
(författare)
-
Enhanced LWIR response of InP/InAsP quantum discs-in-nanowire array photodetectors by photogating and ultra-thin ITO contacts
- 2024
-
Ingår i: Nanotechnology. - Bristol : Institute of Physics Publishing (IOPP). - 0957-4484 .- 1361-6528. ; 35:21, s. 1-7
-
Tidskriftsartikel (refereegranskat)abstract
- Here we report on an experimental and theoretical investigation of the long-wavelength infrared (LWIR) photoresponse of photodetectors based on arrays of three million InP nanowires with axially embedded InAsP quantum discs. An ultra-thin top indium tin oxide contact combined with a novel photogating mechanism facilitates an improved LWIR normal incidence sensitivity in contrast to traditional planar quantum well photodetectors. The electronic structure of the quantum discs, including strain and defect-induced photogating effects, and optical transition matrix elements were calculated by an 8-band k center dot p simulation along with solving drift-diffusion equations to unravel the physics behind the generation of narrow linewidth intersubband signals observed from the quantum discs © 2024 The Author(s). Published by IOP Publishing Ltd.
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| 38. |
- Kohut, A., et al.
(författare)
-
From plasma to nanoparticles : Optical and particle emission of a spark discharge generator
- 2017
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 28:47
-
Tidskriftsartikel (refereegranskat)abstract
- The increased demand for high purity nanoparticles (NPs) of defined geometry necessitates the continuous development of generation routes. One of the most promising physical techniques for producing metal, semiconductor or alloy NPs in the gas phase is spark discharge NP generation. The technique has a great potential for up-scaling without altering the particles. Despite the simplicity of the setup, the formation of NPs in a spark discharge takes place via complex multi-scale processes, which greatly hinders the investigation via conventional NP measurement techniques. In the present work, time-resolved optical emission spectroscopy (OES) was used to provide information on the species present in the spark from as early as approximately 100 ns after the initiation of the discharge. We demonstrate that operando emission spectroscopy can deliver valuable insights into NP formation. The emission spectra of the spark are used to identify, among others, the main stages of material erosion and to calculate the quenching rate of the generated metal vapour. We demonstrate that the alteration of key control parameters, that are typically used to optimize NP generation, clearly affect the emission spectra. We report for Cu and Au NPs that the intensity of spectral lines emitted by metal atoms levels off when spark energy is increased above an energy threshold, suggesting that the maximum concentration of metal vapour produced in the generator is limited. This explains the size variation of the generated NPs. We report a strong correlation between the optical and particle emission of the spark discharge generator, which demonstrate the suitability of OES as a valuable characterization tool that will allow for the more deliberate optimization of spark-based NP generation.
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| 39. |
- Kumar, Sandeep, et al.
(författare)
-
Evaluation of carrier density and mobility in Mn ion-implanted GaAs:Zn nanowires by Raman spectroscopy
- 2020
-
Ingår i: Nanotechnology. - Bristol : IOP Publishing. - 0957-4484 .- 1361-6528. ; 31:20
-
Tidskriftsartikel (refereegranskat)abstract
- The fabrication of complex nanoscale electronics with reduced dimensions poses challenges on novel techniques to accurately determine fundamental electronic parameters. In this article, we present a universal contactless method based on Raman scattering for measuring the mobility and hole concentration independently in GaAs:Zn and Mn ion-implanted GaAs:Zn nanowires, potentially of great interest for spintronics applications. Clear coupled longitudinal optical phonon-plasmon modes were recorded and fitted with a dielectric function, based on the Drude model, which includes contributions from both plasmons and phonons. From the fitting, we extract accurate values of the plasma frequency and plasma damping constant from which we directly calculate the hole density and mobility, respectively. The extracted mobilities were also used as input data for analysis of complementary four-probe transport measurements, where the corresponding hole concentrations could be calculated and found to be in good agreement with those extracted directly from the Raman data. We also investigated the influence of annealing of the GaAs:Zn nanowires on the hole concentration and mobility and found strong indications of thermally activated defects related to a formed crystalline As/oxide shell around the nanowires. The method proposed here is extremely powerful for the characterization of nanoelectronics in general, and nanospintronics in particular for which Hall measurements are difficult to pursue due to problems related to contact formation, as well as to inherent magnetic properties of the devices.
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| 40. |
- Lard, Mercy, et al.
(författare)
-
Biosensing using arrays of vertical semiconductor nanowires : mechanosensing and biomarker detection
- 2019
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 30:21
-
Tidskriftsartikel (refereegranskat)abstract
- Due to their high aspect ratio and increased surface-to-foot-print area, arrays of vertical semiconductor nanowires are used in numerous biological applications, such as cell transfection and biosensing. Here we focus on two specific valuable biosensing approaches that, so far, have received relatively limited attention in terms of their potential capabilities: cellular mechanosensing and lightguiding-induced enhanced fluorescence detection. Although proposed a decade ago, these two applications for using vertical nanowire arrays have only very recently achieved significant breakthroughs, both in terms of understanding their fundamental phenomena, and in the ease of their implementation. We review the status of the field in these areas and describe significant findings and potential future directions.
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| 41. |
- Leshchenko, E. D., et al.
(författare)
-
Tuning the morphology of self-assisted GaP nanowires
- 2018
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 29:22
-
Tidskriftsartikel (refereegranskat)abstract
- Patterned arrays of self-assisted GaP nanowires (NWs) were grown on a Si substrate by gas source molecular beam epitaxy using various V/III flux ratios from 1-6, and various pitches from 360-1000 nm. As the V/III flux ratio was increased from 1-6, the NWs showed a change in morphology from outward tapering to straight, and eventually to inward tapering. The morphologies of the self-assisted GaP NWs are well described by a simple kinetic equation for the NW radius versus the position along the NW axis. The most important growth parameter that governs the NW morphology is the V/III flux ratio. Sharpened NWs with a stable radius equal to only 12 nm at a V/III flux of 6 were achieved, demonstrating their suitability for the insertion of quantum dots.
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| 42. |
- Limpert, Steven, et al.
(författare)
-
Single-nanowire, low-bandgap hot carrier solar cells with tunable open-circuit voltage
- 2017
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 28:43
-
Tidskriftsartikel (refereegranskat)abstract
- Compared to traditional pn-junction photovoltaics, hot carrier solar cells offer potentially higher efficiency by extracting work from the kinetic energy of photogenerated 'hot carriers' before they cool to the lattice temperature. Hot carrier solar cells have been demonstrated in high-bandgap ferroelectric insulators and GaAs/AlGaAs heterostructures, but so far not in low-bandgap materials, where the potential efficiency gain is highest. Recently, a high open-circuit voltage was demonstrated in an illuminated wurtzite InAs nanowire with a low bandgap of 0.39 eV, and was interpreted in terms of a photothermoelectric effect. Here, we point out that this device is a hot carrier solar cell and discuss its performance in those terms. In the demonstrated devices, InP heterostructures are used as energy filters in order to thermoelectrically harvest the energy of hot electrons photogenerated in InAs absorber segments. The obtained photovoltage depends on the heterostructure design of the energy filter and is therefore tunable. By using a high-resistance, thermionic barrier, an open-circuit voltage is obtained that is in excess of the Shockley-Queisser limit. These results provide generalizable insight into how to realize high voltage hot carrier solar cells in low-bandgap materials, and therefore are a step towards the demonstration of higher efficiency hot carrier solar cells.
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| 43. |
- Lindelöw, F., et al.
(författare)
-
Gated Hall effect measurements on selectively grown InGaAs nanowires
- 2017
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 28:20
-
Tidskriftsartikel (refereegranskat)abstract
- InGaAs nanowires is one of the promising material systems of replacing silicon in future CMOS transistors, due to its high electron mobility in combination with the excellent electrostatic control from the tri-gate geometry. In this article, we report on gated Hall measurements on single and multiple In0.85Ga0.15As nanowires, selectively grown in a Hall bridge geometry with nanowire widths down to 50 nm and thicknesses of 10 nm. The gated nanowires can be used as junctionless transistors, which allows for a simplified device processing as no regrowth of contact layer or ion implantation is needed, which is particularly beneficial as transistor dimensions are scaled down. The analysis shows that the InGaAs layer has a carrier concentration of above 1019 cm-3, with a Hall carrier mobility of around 1000 cm2 V-1 s-1. The gated Hall measurements reveal an increased carrier concentration as a function of applied gate voltage, with an increasing mobility for narrow nanowires but no significant effect on larger nanowires.
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| 44. |
- Löfstrand, Anette, et al.
(författare)
-
Feature size control using surface reconstruction temperature in block copolymer lithography for InAs nanowire growth
- 2020
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 31:32
-
Tidskriftsartikel (refereegranskat)abstract
- Here we present a method to control the size of the openings in hexagonally organized BCP thin films of poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP) by using surface reconstruction. The surface reconstruction is based on selective swelling of the P4VP block in ethanol, and its extraction to the surface of the film, resulting in pores upon drying. We found that the BCP pore diameter increases with ethanol immersion temperature. In our case, the temperature range 18 to 60 °C allowed fine-Tuning of the pore size between 14 and 22 nm. A conclusion is that even though the molecular weight of the respective polymer blocks is fixed, the PS-b-P4VP pore diameter can be tuned by controlling temperature during surface reconstruction. These results can be used for BCP-based nanofabrication in general, and for vertical nanowire growth in particular, where high pattern density and diameter control are of importance. Finally, we demonstrate successful growth of indium arsenide InAs vertical nanowires by selective-Area metal-organic vapor phase epitaxy (MOVPE), using a silicon nitride mask patterned by the proposed PS-b-P4VP surface reconstruction lithography method.
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| 45. |
- Maliakkal, Carina B., et al.
(författare)
-
Post-nucleation evolution of the liquid-solid interface in nanowire growth
- 2022
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 33:10
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Tidskriftsartikel (refereegranskat)abstract
- We study using in situ transmission electron microscopy the birth of GaAs nanowires from liquid Au-Ga catalysts on amorphous substrates. Lattice-resolved observations of the starting stages of growth are reported here for the first time. It reveals how the initial nanostructure evolves into a nanowire growing in a zincblende 111 or the equivalent wurtzite0001 direction. This growth direction(s) is what is typically observed in most III-V and II-VI nanowires. However, the reason for this preferential nanowire growth along this direction is still a dilemma. Based on the videos recorded shortly after the nucleation of nanowires, we argue that the lower catalyst droplet-nanowire interface energy of the {111} facet when zincblende (or the equivalent {0001} facet in wurtzite) is the reason for this direction selectivity in nanowires.
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| 46. |
- Memisevic, Elvedin, et al.
(författare)
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Impact of source doping on the performance of vertical InAs/InGaAsSb/GaSb nanowire Tunnel Field-Effect Transistors
- 2018
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 29:43
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we analyze experimental data from state-of-the-art vertical InAs/InGaAsSb/GaSb nanowire Tunnel Field-Effect Transistors to study influence of the source doping on their performance. Overall, the doping level impacts both off-state and on-state performance of these devices. Separation of the doping from the heterostructure improved the subthreshod swing of the devices. Best devices reached a point subthreshold swing of 30 mV/dec at 100x higher currents than what Si-based TFETs has achieved previously. However, separation of doping from the heterostructure had a significant impact on the on-state performance of these devices due to effects related to source depletion. Increase of the doping level, helped to improve the on-state performance, which also increased the subthreshold swing. Thus, further optimization of doping incorporation at the heterostructure will help to improve vertical InAs/InGaAsSb/GaSb nanowire TFETs.
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| 47. |
- Menon, Heera, et al.
(författare)
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Improved quality of InSb-on-insulator microstructures by flash annealing into melt
- 2021
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 32:16
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Tidskriftsartikel (refereegranskat)abstract
- Monolithic integration of III-V semiconductors with Silicon technology has instigated a wide range of new possibilities in the semiconductor industry, such as combination of digital circuits with optical sensing and high-frequency communication. A promising CMOS compatible integration process is rapid melt growth (RMG) that can yield high quality single crystalline material at low cost. This paper represents the study on ultra-thin InSb-on-insulator microstructures integrated on a Si platform by a RMG-like process. We utilize flash lamp annealing (FLA) to melt and recrystallize the InSb material for an ultra-short duration (milliseconds), to reduce the thermal budget necessary for integration with Si technology. We compare the result from FLA to regular rapid thermal annealing (seconds). Recrystallized InSb was characterized using electron back scatter diffraction which indicate a transition from nanocrystalline structure to a crystal structure with grain sizes exceeding 1 μm after the process. We further see a 100× improvement in electrical resistivity by FLA annealed sample when compared to the as-deposited InSb with an average Hall mobility of 3100 cm2 V−1 s−1 making this a promising step towards realizing monolithic mid-infrared detectors and quantum devices based on InSb.
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| 48. |
- Metaferia, Wondwosen, et al.
(författare)
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N-type doping and morphology of GaAs nanowires in Aerotaxy
- 2018
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 29:28
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Tidskriftsartikel (refereegranskat)abstract
- Controlled doping in semiconductor nanowires modifies their electrical and optical properties, which are important for high efficiency optoelectronic devices. We have grown n-type (Sn) doped GaAs nanowires in Aerotaxy, a new continuous gas phase mass production technique. The morphology of Sn doped nanowires is found to be a strong function of dopant, tetraethyltin to trimethylgallium flow ratio, Au-Ga-Sn alloying, and nanowire growth temperatures. High temperature and high flow ratios result in low morphological quality nanowires and in parasitic growth on the wire base and surface. Alloying and growth temperatures of 400 °C and 530 °C, respectively, resulted in good morphological quality nanowires for a flow ratio of TESn to TMGa up to 2.25 ×10-3. The wires are pure zinc-blende for all investigated growth conditions, whereas nanowires grown by metal-organic vapor phase epitaxy with the same growth conditions are usually mainly Wurtzite. The growth rate of the doped wires is found to be dependent more on the TESn flow fraction than on alloying and nanowire growth temperatures. Our photoluminescence measurements, supported by four-point probe resistivity measurements, reveal that the carrier concentration in the doped wires varies only slightly (1-3) ×1019 cm-3 with TESn flow fraction and both alloying and growth temperatures, indicating that good morphological quality wires with high carrier density can be grown with low TESn flow. Carrier concentrations lower than 1019 cm-3 can be grown by further reducing the flow fraction of TESn, which may give better morphology wires.
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| 49. |
- Namazi, Luna, et al.
(författare)
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Direct nucleation, morphology and compositional tuning of InAs1-xSb x nanowires on InAs (111) B substrates
- 2017
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 28:16
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Tidskriftsartikel (refereegranskat)abstract
- III-V ternary nanowires are interesting due to the possibility of modulating their physical and material properties by tuning their material composition. Amongst them InAs1-xSb x nanowires are good candidates for applications such as Infrared detectors. However, this material has not been grown directly from substrates, in a large range of material compositions. Since the properties of ternaries are alterable by tuning their composition, it is beneficial to gain access to a wide range of composition tunability. Here we demonstrate direct nucleation and growth of InAs1-xSb x nanowires from Au seed particles over a broad range of compositions (x = 0.08-0.75) for different diameters and surface densities by means of metalorganic vapor phase epitaxy. We investigate how the nucleation, morphology, solid phase Sb content, and growth rate of these nanowires depend on the particle dimensions, and on growth conditions such as the vapor phase composition, V/III ratio, and temperature. We show that the solid phase Sb content of the nanowires remains invariant towards changes of the In precursor flow. We also discuss that at relatively high In flows the growth mechanism alters from Au-seeded to what is referred to as semi In-seeded growth. This change enables growth of nanowires with a high solid phase Sb content of 0.75 that are not feasible via Au-seeded growth. Independent of the growth conditions and morphology, we report that the nanowire Sb content changes over their length, from lower Sb contents at the base, increasing to higher amounts towards the tip. We correlate the axial Sb content variations to the axial growth rate measured in situ. We also report spontaneous core-shell formation for Au-seeded nanowires, where the core is Sb-rich in comparison to the Sb-poor shell.
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| 50. |
- Potts, Heidi, et al.
(författare)
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Large-bias spectroscopy of Yu-Shiba-Rusinov states in a double quantum dot
- 2023
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 34:13
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Tidskriftsartikel (refereegranskat)abstract
- We have performed tunnel transport spectroscopy on a quantum dot (QD) molecule proximitized by a superconducting contact. In such a system, the scattering between QD spins and Bogoliubov quasiparticles leads to the formation of Yu-Shiba-Rusinov (YSR) states within the superconducting gap. In this work, we investigate interactions appearing when one- and two-electron spin states in a double-QD energetically align with the superconducting gap edge. We find that the inter-dot spin-triplet state interacts considerably stronger with the superconductor than the corresponding singlet, pointing to stronger screening. By forming a ring molecule with a significant orbital contribution to the effective g-factor, we observe interactions of all four spin-orbital one-electron states with the superconductor under a weak magnetic field.
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