| 1. |
- Berggren, Magnus, et al.
(författare)
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Controlling inter-chain and intra-chain excitations of a poly(thiophene) derivative in thin films
- 1999
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Ingår i: Chemical Physics Letters. - : Elsevier. - 0009-2614 .- 1873-4448. ; 304:1-2, s. 84-90
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Tidskriftsartikel (refereegranskat)abstract
- The decay of photoexcitations in polythiophene chains has been studied in solid solutions of the polymer from room temperature to 4 K. A strong blue shift of the emission spectrum is observed in the polymer blend, as compared to the homopolymer. Dispersion of the polythiophene suppresses the non-radiative processes, which are suggested to be correlated to close contacts of polymer chains. Quantum chemistry modeling of the excited state distributed on two chains corroborate this conclusion.
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| 2. |
- Gorji, Sepideh, et al.
(författare)
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Self-catalyzed MBE grown GaAs/GaAsxSb1-x core-shell nanowires in ZB and WZ crystal structures
- 2013
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 24:40
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the growth of self-catalyzed GaAs/GaAsxSb1-x core-shell nanowires directly on Si(111) substrates by molecular beam epitaxy. The compositions of the GaAsxSb1-x shells are tuned in a wide range where the Sb-content is varied from 10 to similar to 70%, covering the miscibility gap. In addition, the GaAsxSb1-x shells are grown on both zinc blende (ZB) and wurtzite (WZ) crystal structures. Morphological and structural characterizations of the grown nanowires indicate successful transfer of the GaAs core crystal structure to the GaAsxSb1-x shells for both ZB and WZ nanowires, with slower shell growth rate on the WZ segments.
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| 3. |
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| 4. |
- Karlsson, Fredrik, 1974-, et al.
(författare)
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Electroluminescence and photoluminescence excitation study of asymmetric coupled GaAs/AlxGa1-xAs V-groove quantum wires
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 70:4
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Tidskriftsartikel (refereegranskat)abstract
- We have studied systems of asymmetric coupled GaAs V-groove quantum wires p-i-n diodes, in which the electrons and holes are injected into different wires. Despite the use of a 7 nm thick AlGaAs tunnel barrier, and although we demonstrate that holes tunnel more slowly than electrons, we observe a very efficient and fast tunneling between the quantum wires (QWR's). We attribute this to the achievement of a resonance between hole levels in the two QWR's. Photoluminescence excitation experiments are compared with accurate calculations of the excitonic absorption yielding a level of carrier transfer of nearly 100%. Temperature-dependent electroluminescence exhibits clear effects of tunneling up to room temperature but cannot distinguish separate electron/hole tunneling from exciton tunneling.
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| 5. |
- Karlsson, Fredrik, 1974-, et al.
(författare)
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Electrolummescence of asymmetric coupled GaAs/AlGaAs V-groove quantum wires
- 2003
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Ingår i: Institute of Physics Conference Series. - 0951-3248 .- 2154-6630. ; 174, s. 183-186
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Tidskriftsartikel (refereegranskat)abstract
- We have studied systems of asymmetric coupled GaAs V-groove quantum wires, in which the electrons and holes are injected into different wires. Our experimental results indicate efficient electron and hole tunneling, despite a 7 nm thick AlGaAs tunnel barrier. Temperature dependent electroluminescence exhibit clear effects of tunneling up to room temperature but cannot distinguish electron/hole tunneling from exciton tunneling.
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| 6. |
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| 7. |
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| 8. |
- Karlsson, Fredrik, 1974-, et al.
(författare)
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Fractional-dimensional excitonic absorption theory applied to V-groove quantum wires
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 70:15
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Tidskriftsartikel (refereegranskat)abstract
- A fractional-dimensional approach is applied to a realistic V-groove quantum wire in order to calculate the excitonic absorption spectrum. An excellent agreement is obtained with much more computationally demanding models as well as with experimental photoluminescence excitation data. However, comparison with a full excitonic calculation reveals situations were the concept of fractional dimensions to some extent fails.
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| 9. |
- Karlsson, Fredrik, 1974-, et al.
(författare)
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Strongly reduced exciton transfer between parallel quantum wires
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:10, s. 101108-101108-3
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Tidskriftsartikel (refereegranskat)abstract
- Exciton transfer between two parallel GaAs V-groove quantum wires or two planar quantum wells separated by AlGaAs barriers ranging from 5.5 nm to 20 nm thickness is studied by photoluminescence and photoluminescence excitation spectroscopy. It is found that the transfer is strongly reduced between the widely spaced quantum wires as compared with quantum wells. This observation is supported by model calculations, which yield strong dimensionality dependence of the photon-exchange transfer.
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| 10. |
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| 11. |
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| 12. |
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| 13. |
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| 14. |
- Palmgren, Susanna, 1969-, et al.
(författare)
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Polarization-resolved optical absorption in single V-groove quantum wires
- 2006
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89, s. 191111-
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Tidskriftsartikel (refereegranskat)abstract
- Optical transitions associated with all three linear polarization directions were investigated in single GaAs V-groove quantum wires of different wire thicknesses. This was accomplished by combining absorption measurements in V-groove waveguide geometry with surface-excited photoluminescence excitation spectroscopy. The observed transitions were identified with the aid of model calculations. It is shown that excitonic intersubband coupling should be accounted for in order to explain the optical transitions associated with confined light-hole-like states. The results are relevant for the design of efficient quantum wire waveguide modulators and lasers.
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| 15. |
- Reichardt, H., et al.
(författare)
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Influence of long-range substrate roughness on disorder in V-groove quantum wire structures
- 2006
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 100, s. 123509-
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Tidskriftsartikel (refereegranskat)abstract
- The observation and the interpretation of line splitting in photoluminescence and cathodoluminescence spectra of GaAs/AlGaAs V-groove quantum wires (QWRs) are reported. The QWR emission line splits into two peaks whose intensities oscillate systematically along the axis of the wire. Combining atomic force microscopy and cathodoluminescence measurements, we show a clear correlation between the surface topography of the V-groove and the individual peak intensities. We elucidate the relationship between the V-groove sidewall roughness and the shape at its bottom, and explain their impact on the QWR formation using a two-dimensional growth model accounting for self-limited growth in each V-groove domain. The influence of the long-range substrate roughness on the QWR spectral features is thus clarified. The study provides guidelines for improving QWR uniformity in order to achieve near-ideal model systems for one-dimensional semiconductors
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| 16. |
- Ren, Dingding, et al.
(författare)
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New Insights into the Origins of Sb-Induced Effects on Self-Catalyzed GaAsSb Nanowire Arrays.
- 2016
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 16:2, s. 1201-1209
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Tidskriftsartikel (refereegranskat)abstract
- Ternary semiconductor nanowire arrays enable scalable fabrication of nano-optoelectronic devices with tunable bandgap. However, the lack of insight into the effects of the incorporation of Vy element results in lack of control on the growth of ternary III-V1-yVy nanowires and hinders the development of high-performance nanowire devices based on such ternaries. Here, we report on the origins of Sb-induced effects affecting the morphology and crystal structure of self-catalyzed GaAsSb nanowire arrays. The nanowire growth by molecular beam epitaxy is changed both kinetically and thermodynamically by the introduction of Sb. An anomalous decrease of the axial growth rate with increased Sb2 flux is found to be due to both the indirect kinetic influence via the Ga adatom diffusion induced catalyst geometry evolution and the direct composition modulation. From the fundamental growth analyses and the crystal phase evolution mechanism proposed in this Letter, the phase transition/stability in catalyst-assisted ternary III-V-V nanowire growth can be well explained. Wavelength tunability with good homogeneity of the optical emission from the self-catalyzed GaAsSb nanowire arrays with high crystal phase purity is demonstrated by only adjusting the Sb2 flux.
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| 17. |
- Ren, Dingding, et al.
(författare)
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Single-Mode Near-Infrared Lasing in a GaAsSb-Based Nanowire Superlattice at Room Temperature
- 2018
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 18:4, s. 2304-2310
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Tidskriftsartikel (refereegranskat)abstract
- Semiconductor nanowire lasers can produce guided coherent light emission with miniaturized geometry, bringing about new possibilities for a variety of applications including nanophotonic circuits, optical sensing, and on-chip and chip-to-chip optical communications. Here, we report on the realization of single-mode and room-temperature lasing from 890 to 990 nm, utilizing a novel design of single nanowires with GaAsSb-based multiple axial superlattices as a gain medium under optical pumping. The control of lasing wavelength via compositional tuning with excellent room-temperature lasing performance is shown to result from the unique nanowire structure with efficient gain material, which delivers a low lasing threshold of ∼6 kW/cm2 (75 μJ/cm2 per pulse), a lasing quality factor as high as 1250, and a high characteristic temperature of ∼129 K. These results present a major advancement for the design and synthesis of nanowire laser structures, which can pave the way toward future nanoscale integrated optoelectronic systems with superior performance.
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| 18. |
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| 19. |
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| 20. |
- Weman, Helge, 1960-, et al.
(författare)
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High internal quantum efficiency, narrow linewidth emission InGaAs/GaAs/AlGaAs quantum wire light-emitting diode
- 2002
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 81:15, s. 2839-2841
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Tidskriftsartikel (refereegranskat)abstract
- High internal quantum efficiency (similar to60%), narrow linewidth (as narrow as 14 meV) exciton emission at room temperature has been obtained using strained InGaAs V-groove quantum wire (QWR) light-emitting diodes (LEDs). The high efficiency is achieved with the aid of selective carrier injection through self-ordered AlGaAs vertical quantum wells (VQWs), where the VQWs are separated from the InGaAs QWRs by thin GaAs spacer layers in order to reduce nonradiative recombination and inhomogeneous alloy broadening. Evidence for excitonic recombination in these LEDs up to RT is provided by measurements of the emission energy shifts at high magnetic fields.
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| 21. |
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| 22. |
- Weman, Helge, 1960-, et al.
(författare)
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Semiconductor Quantum-Wires and Nano-Wires for optoelectronic Applications
- 2009
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Ingår i: Journal of materials science. Materials in electronics. - : Springer Science and Business Media LLC. - 0957-4522 .- 1573-482X. ; 20:1, s. S94-S101
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Tidskriftsartikel (refereegranskat)abstract
- Exciton transfer between two parallel GaAs V-groove quantum wires (QWRs) or two planar quantum wells (QWs) separated by AlGaAs barriers ranging from 5.5 nm to 20 nm thickness is studied by photoluminescence (PL) and PL excitation (PLE) spectroscopy. It is found that the transfer is strongly reduced between the widely spaced QWRs as compared with QWs. We have also investigated the optical absorption in single QWRs embedded in an AlGaAs V-shaped channel waveguide. Using a combination of PLE and absorption measurements we construct the full dependence of absorption spectra on the linear polarization. Our studies reveal the importance of inter-subband mixing in determining the energies of the light-hole-like transitions and thus the QWR absorption. Finally we present recent results on the fabrication and structural characterization of GaAs and GaP nanowires (NWs) grown by molecular beam epitaxy (MBE) on GaAs(111)B and Si(111) substrates, using Au-catalyzed vapor–liquid–solid growth technique. It is shown that, apart from optimizing the NW growth parameters, substrate material and the procedure for preparing the substrate before the MBE growth play an important role in controlling the NWs.
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