| 1. |
- Holmér, Jonatan, 1990, et al.
(author)
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An STM – SEM setup for characterizing photon and electron induced effects in single photovoltaic nanowires
- 2018
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In: Nano Energy. - : Elsevier BV. - 2211-2855. ; 53, s. 175-181
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Journal article (peer-reviewed)abstract
- Vertical arrays of semiconductor nanowires show great potential for material-efficient and high-performance solar cells. The characterization and correlation between material structure and properties of the individual nanowires are crucial for the continued performance improvement of such devices. In this work, we developed a method with a scanning tunneling microscope (STM) probe inside a scanning electron microscope (SEM) to enable the studies of single photovoltaic nanowires. The STM probe is used to contact individual nanowires in ensembles. We combine the STM-SEM with an in situ light emitting diode (LED) illumination source to study both the electrical and photovoltaic properties of vertical GaAs nanowires with radial p-i-n junctions. We also illustrate that the local charge separation ability within the nanowires can be studied by electron beam induced current (EBIC) measurements. The in situ SEM setup allows the correlation between properties and nanowire structure. The data show that the quality of the electrical contact to the semiconductor nanowire is crucial to be able to investigate the inherent properties of the nanowires. We have established a procedure to make high-quality ohmic contacts to the nanowires with the STM probe. We also show that the effect of mechanical strain on the electrical properties can be investigated by the STM-SEM setup.
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| 2. |
- Holmér, Jonatan, 1990, et al.
(author)
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Enhancing the NIR Photocurrent in Single GaAs Nanowires with Radial p-i-n Junctions by Uniaxial Strain
- 2021
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In: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 2:21, s. 9038-9043
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Journal article (peer-reviewed)abstract
- III-V compound nanowires have electrical and optical properties suitable for a wide range of applications, including photovoltaics and photodetectors. Furthermore, their elastic nature allows the use of strain engineering to enhance their performance. Here we have investigated the effect of mechanical strain on the photocurrent and the electrical properties of single GaAs nanowires with radial p-i-n junctions, using a nanoprobing setup. A uniaxial tensile strain of 3% resulted in an increase in photocurrent by more than a factor of 4 during NIR illumination. This effect is attributed to a decrease of 0.2 eV in nanowire bandgap energy, revealed by analysis of the current-voltage characteristics as a function of strain. This analysis also shows how other properties are affected by the strain, including the nanowire resistance. Furthermore, electron-beam-induced current maps show that the charge collection efficiency within the nanowire is unaffected by strain measured up to 0.9%.
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| 3. |
- Meyer-Holdt, J., et al.
(author)
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Ag-catalyzed InAs nanowires grown on transferable graphite flakes
- 2016
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In: Nanotechnology. - : IOP Publishing. - 1361-6528 .- 0957-4484. ; 27:36
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Journal article (peer-reviewed)abstract
- Semiconducting nanowires grown by quasi-van-der-Waals epitaxy on graphite flakes are a new class of hybrid materials that hold promise for scalable nanostructured devices within opto-electronics. Here we report on high aspect ratio and stacking fault free Ag-seeded InAs nanowires grown on exfoliated graphite flakes by molecular beam epitaxy. Ag catalyzes the InAs nanowire growth selectively on the graphite flakes and not on the underlying InAs substrates. This allows for easy transfer of the flexible graphite flakes with as-grown nanowire ensembles to arbitrary substrates by a micro-needle manipulator. Besides the possibilities for fabricating novel nanostructure device designs, we show how this method is used to study the parasitic growth and bicrystal match between the graphite flake and the nanowires by transmission electron microscopy.
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| 4. |
- Zeng, Lunjie, 1983, et al.
(author)
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The Effect of Bending Deformation on Charge Transport and Electron Effective Mass of p-doped GaAs Nanowires
- 2019
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In: Physica Status Solidi - Rapid Research Letetrs. - : Wiley. - 1862-6254 .- 1862-6270. ; 13:8
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Journal article (other academic/artistic)abstract
- The crystal and electronic structure of semiconductor nanowire systems have shown sensitive response to mechanical strain, enabling novel and improved electrical, and optoelectrical properties in nanowires by strain engineering. Here, the response of current–voltage (I–V) characteristics and band structure of individual p-doped GaAs nanowires to bending deformation is studied by in situ electron microscopy combined with theoretical simulations. The I–V characteristics of the nanowire change from linear to nonlinear as bending deformation is applied. The nonlinearity increases with strain. As opposed to the case of uniaxial strain in GaAs, the bending deformation does not give rise to a change in the band gap of GaAs nanowire according to in situ electron energy loss spectroscopy (EELS) measurements. Instead, the response to bending deformation can be explained by strain induced valence band shift, which results in an energy barrier for charge carrier transport along the nanowire. Moreover, the electron effective mass decreases as the strain changes from compressive to tensile across the GaAs nanowire in the bent region. Results from this study shed light on the complex interplay between lattice strain, band structure, and charge transport in semiconductor nanomaterials.
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