| 1. |
- Anttu, Nicklas, et al.
(författare)
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Reflection measurements to reveal the absorption in nanowire arrays
- 2013
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Ingår i: Optics Letters. - 0146-9592. ; 38:9, s. 1449-1451
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Tidskriftsartikel (refereegranskat)abstract
- The absorption of light is at the core of photovoltaic applications. For many nanostructure-based devices, an assessment of the absorption in the nanostructures is complicated by a thick, opaque substrate that prohibits transmission measurements. Here, we show how a single reflection measurement can be used for approximating the amount of light absorbed in vertical semiconductor nanowire arrays. (C) 2013 Optical Society of America
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| 2. |
- Mante, Pierre Adrien, et al.
(författare)
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Confinement effects on Brillouin scattering in semiconductor nanowire photonic crystal
- 2016
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Ingår i: Physical Review B. - 1098-0121. ; 94:2
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Tidskriftsartikel (refereegranskat)abstract
- Scattering of photons by phonons, or Brillouin scattering, enables manipulation and control of light and has led to revolutionary applications, from slow light to saser and cooling of micromechanical resonators. Recently, enhanced light and sound interaction has been demonstrated in waveguides. However, the design of the waveguide geometry tunes and alters the phonon and photon dispersion simultaneously. Here we investigate, through femtosecond pump-probe spectroscopy and theoretical modeling, the light and sound interaction in a bottom-up fabricated vertical nanowire photonic crystal. In such a system, the phonon dispersion can be tuned by varying the geometry of the constituent nanowires. In contrast, the placement of the nanowires in the photonic crystal can be used for tuning optical array modes, without altering the phonon dispersion. We demonstrate the forward and backward scattering, by acoustic phonons in the nanowires, of (1) such optical array modes and (2) guided modes of the constituent nanowires. Furthermore, our results reveal an enhanced interaction of array modes with phonons that we attribute to the specific scattering mechanism. Our results enable the design of a photonic crystal with separately tailored photon and phonon dispersion for Brillouin scattering. We anticipate these advances to be a starting point for enhanced control of light at the nanoscale.
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| 3. |
- Alcer, David, et al.
(författare)
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Comparison of Triethylgallium and Trimethylgallium Precursors for GaInP Nanowire Growth
- 2021
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Ingår i: Physica Status Solidi (B) Basic Research. - : Wiley. - 0370-1972. ; 258:2
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Tidskriftsartikel (refereegranskat)abstract
- Nanowire (NW) arrays containing a top segment of GaxIn1–xP are investigated, comparing NWs grown using two different Ga precursors, trimethylgallium (TMGa) and triethylgallium (TEGa). TMGa is the precursor commonly used for the particle-assisted vapor–liquid–solid (VLS) growth of GaxIn1–xP NWs. However, it shows inefficient pyrolysis at typical NW growth conditions. The use of the alternative precursor TEGa is investigated by making a direct comparison between NWs grown using TEGa and TMGa at otherwise identical growth conditions. Growth rates, resulting NW materials composition, and time-resolved photoluminescence (TRPL) lifetimes are investigated. With increasing Ga content of the NWs, the TRPL lifetimes decrease, indicating trap states that are associated with GaP. Somewhat longer TRPL lifetimes for the samples grown using TEGa indicate a lower concentration of deep trap states. For doped NWs, it is found that the strong effect of the p-type dopant diethylzinc (DEZn) on the NW composition, observed for GaxIn1–xP NWs grown using TMGa, is absent when using TEGa.
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| 4. |
- Hrachowina, Lukas, et al.
(författare)
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Imaging the influence of oxides on the electrostatic potential of photovoltaic InP nanowires
- 2021
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Ingår i: Nano Research. - : Springer Science and Business Media LLC. - 1998-0124 .- 1998-0000. ; 14:11, s. 4087-4092
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Tidskriftsartikel (refereegranskat)abstract
- Nanowires require surface passivation due to their inherent large surface to volume ratio. We investigate the effect of embedding InP nanowires in different oxides with respect to surface passivation by use of electron beam induced current measurements enabled by a nanoprobe based system inside a scanning electron microscope. The measurements reveal remote doping due to fixed charge carriers in the passivating POx/Al2O3 shell in contrast to results using SiOx. We used time-resolved photoluminescence to characterize the lifetime of charge carriers to evaluate the success of surface passivation. In addition, spatially resolved internal quantum efficiency simulations support and correlate the two applied techniques. We find that atomic-layer deposited POx/Al2O3 has the potential to passivate the surface of InP nanowires, but at the cost of inducing a field-effect on the nanowires, altering their electrostatic potential profile. The results show the importance of using complementary techniques to correctly evaluate and interpret processing related effects for optimization of nanowire-based optoelectronic devices. [Figure not available: see fulltext.].
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| 5. |
- Iqbal, Azhar, et al.
(författare)
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Photoluminescence study of as-grown vertically standing wurtzite InP nanowire ensembles.
- 2013
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 24:11
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a method that enables the study of photoluminescence of as-grown nanowires on a native substrate by non-destructively suppressing the contribution of substrate photoluminescence. This is achieved by using polarized photo-excitation and photoluminescence and by making an appropriate choice of incident angle of both excitation beam and photoluminescence collection direction. Using T-polarized excitation at a wavelength of 488 nm at an incident angle of ∼70° we suppress the InP substrate photoluminescence relative to that of the InP nanowires by about 80 times. Consequently, the photoluminescence originating from the nanowires becomes comparable to and easily distinguishable from the substrate photoluminescence. The measured photoluminescence, which peaks at photon energies of ∼1.35 eV and ∼1.49 eV, corresponds to the InP substrate with zinc-blende crystal structure and to the InP nanowires with wurtzite crystal structure, respectively. The photoluminescence quantum yield of the nanowires was found to be ∼20 times lower than that of the InP substrate. The nanowires, grown vertically in a random ensemble, neither exhibit substantial emission polarization selectivity to the axis of the nanowires nor follow excitation polarization preferences observed previously for a single nanowire.
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| 6. |
- Irish, Austin, et al.
(författare)
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Nitrogen plasma passivation of GaAs nanowires resolved by temperature dependent photoluminescence
- 2022
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Ingår i: NANO EXPRESS. - : Institute of Physics (IOP). - 2632-959X. ; 3:4
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a significant improvement in the optical performance of GaAs nanowires achieved using a mixed nitrogen-hydrogen plasma which passivates surface states and reduces the rate of nonradiative recombination. This has been confirmed by time-resolved photoluminescence measurements. At room temperature, the intensity and lifetime of radiative recombination in the plasma-treated nanowires was several times greater than that of the as-grown GaAs nanowires. Low-temperature measurements corroborated these findings, revealing a dramatic increase in photoluminescence by two orders of magnitude. Photoelectron spectroscopy of plasma passivated nanowires demonstrated a yearlong stability achieved through the replacement of surface oxygen with nitrogen. Furthermore, the process removed the As-0 defects observed on non-passivated nanowires which are known to impair devices. The results validate plasma as a nitridation technique suitable for nanoscale GaAs crystals. As a simple ex situ procedure with modest temperature and vacuum requirements, it represents an easy method for incorporating GaAs nanostructures into optoelectronic devices.
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| 7. |
- Mante, Pierre-Adrien, et al.
(författare)
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Ultrafast Optical Generation of Coherent Bright and Dark Surface Phonon Polaritons in Nanowires
- 2020
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 7:8, s. 1923-1931
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Tidskriftsartikel (refereegranskat)abstract
- The subwavelength confinement and enhanced electric field created by plasmons allow precise sensing and enhanced light–matter interaction. However, the high frequency and short lifetime of plasmons limit the full potential of this technology. It is crucial to find substitutes and to study their dynamics. Here, we propose an experimental approach allowing the time-domain study of surface phonon polaritons. We first build a theoretical framework for the interaction of ultrashort pulses of light with polar materials. We then perform femtosecond pump–probe experiments and demonstrate the generation and time-resolved detection of surface phonon polaritons. By comparing experiments and simulations, we show the presence of both bright and dark modes with quality factors up to 115. We then investigate mode-dependent decay and energy transfer to the environment. Our results offer a platform for the experimental exploration of the dynamics of surface phonon polaritons and of the role of coherence in energy transfer.
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| 8. |
- Mergenthaler, Kilian, et al.
(författare)
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Large-energy-shift photon upconversion in degenerately doped InP nanowires by direct excitation into the electron gas
- 2013
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Ingår i: Nano Reseach. - : Springer Science and Business Media LLC. - 1998-0124 .- 1998-0000. ; 6:10, s. 752-757
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Tidskriftsartikel (refereegranskat)abstract
- Realizing photon upconversion in nanostructures is important for many next-generation applications such as biological labelling, infrared detectors and solar cells. In particular nanowires are attractive for optoelectronics because they can easily be electrically contacted. Here we demonstrate photon upconversion with a large energy shift in highly n-doped InP nanowires. Crucially, the mechanism responsible for the upconversion in our system does not rely on multi-photon absorption via intermediate states, thus eliminating the need for high photon fluxes to achieve upconversion. The demonstrated upconversion paves the way for utilizing nanowires-with their inherent flexibility such as electrical contactability and the ability to position individual nanowires-for photon upconversion devices also at low photon fluxes, possibly down to the single photon level in optimised structures.
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| 9. |
- Mergenthaler, Kilian, et al.
(författare)
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Photon upconversion in degenerately sulfur doped InP nanowires.
- 2015
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 7:48, s. 20503-20509
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Tidskriftsartikel (refereegranskat)abstract
- Radiative recombination in degenerately n-doped InP nanowires is studied for excitation above and below the Fermi energy of the electron gas, using photoluminescence. Laser-induced electron heating is observed, which allows absorption below the Fermi energy. We observe photon upconversion where photo-excited holes recombine with high |k| electrons. This can be attributed to hole scattering to high |k|-values, and the temperature dependence of this process is measured. We show that hole relaxation via phonon scattering can be observed in continuous wave excitation luminescence measurements.
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| 10. |
- Ponseca, Carlito, et al.
(författare)
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Bulk-like transverse electron mobility in an array of heavily n-doped InP nanowires probed by terahertz spectroscopy
- 2014
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 90:8
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Tidskriftsartikel (refereegranskat)abstract
- Terahertz spectroscopy is employed for the noncontact measurement of transversal mobility in InP nanowires, wherein photonic effects (waveguiding of excitation beam and propagation of terahertz beam in a complex gradient environment) were successfully deconvoluted. Monte Carlo calculations accounting for electron localization and heavy doping were used to determine electron momentum relaxation time corresponding to electron mobility >= 3000 cm(2)/Vs, which is similar to that in bulk InP. The developed approach paves a way for noncontact determination of charge mobility in advanced semiconductor nanostructures.
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