| 1. |
- Limpert, Steven, et al.
(författare)
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Single-nanowire, low-bandgap hot carrier solar cells with tunable open-circuit voltage
- 2017
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 28:43
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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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| 2. |
- 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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| 3. |
- Fahlvik Svensson, Sofia, et al.
(författare)
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Control and understanding of kink formation in InAs-InP heterostructure nanowires.
- 2013
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 24:34
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Tidskriftsartikel (refereegranskat)abstract
- Nanowire heterostructures are of special interest for band structure engineering due to an expanded range of defect-free material combinations. However, the higher degree of freedom in nanowire heterostructure growth comes at the expense of challenges related to nanowire-seed particle interactions, such as undesired composition, grading and kink formation. To better understand the mechanisms of kink formation in nanowires, we here present a detailed study of the dependence of heterostructure nanowire morphology on indium pressure, nanowire diameter, and nanowire density. We investigate InAs-InP-InAs heterostructure nanowires grown with chemical beam epitaxy, which is a material system that allows for very abrupt heterointerfaces. Our observations indicate that the critical parameter for kink formation is the availability of indium, and that the resulting morphology is also highly dependent on the length of the InP segment. It is shown that kinking is associated with the formation of an inclined facet at the interface between InP and InAs, which destabilizes the growth and leads to a change in growth direction. By careful tuning of the growth parameters, it is possible to entirely suppress the formation of this inclined facet and thereby kinking at the heterointerface. Our results also indicate the possibility of producing controllably kinked nanowires with a high yield.
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| 4. |
- Ganjipour, Bahram, et al.
(författare)
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Electrical properties of GaSb/InAsSb core/shell nanowires
- 2014
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 25:42
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Tidskriftsartikel (refereegranskat)abstract
- Temperature dependent electronic properties of GaSb/InAsSb core/shell and GaSb nanowires have been studied. Results from two-probe and four-probe measurements are compared to distinguish between extrinsic (contact-related) and intrinsic (nanowire) properties. It is found that a thin (2-3 nm) InAsSb shell allows low barrier charge carrier injection to the GaSb core, and that the presence of the shell also improves intrinsic nanowire mobility and conductance in comparison to bare GaSb nanowires. Maximum intrinsic field effect mobilities of 200 and 42 cm(2) Vs(-1) were extracted for the GaSb/InAsSb core/shell and bare-GaSb NWs at room temperature, respectively. The temperature-dependence of the mobility suggests that ionized impurity scattering is the dominant scattering mechanism in bare GaSb while phonon scattering dominates in core/shell nanowires. Top-gated field effect transistors were fabricated based on radial GaSb/InAsSb heterostructure nanowires with shell thicknesses in the range 5-7 nm. The fabricated devices exhibited ambipolar conduction, where the output current was studied as a function of AC gate voltage and frequency. Frequency doubling was experimentally demonstrated up to 20 kHz. The maximum operating frequency was limited by parasitic capacitance associated with the measurement chip geometry.
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| 5. |
- Gluschke, Jan-Göran, et al.
(författare)
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Fully tunable, non-invasive thermal biasing of gated nanostructures suitable for low-temperature studies.
- 2014
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 25:38
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Tidskriftsartikel (refereegranskat)abstract
- There is much recent interest in the thermoelectric (TE) characterization of single nanostructures at low temperatures, because such measurements yield information that is complementary to traditional conductance measurements, and because they may lead to novel paradigms for TE energy conversion. However, previously reported techniques for thermal biasing of nanostructures are difficult to use at low temperatures because of unintended global device heating, the lack of ability to continuously tune the thermal bias, or limited compatibility with gating techniques. By placing a heater directly on top of the electrical contact to a single InAs nanowire, we demonstrate fully tunable thermal biases of up to several tens of Kelvin, combined with negligible overall heating of the device, and with full functionality of a back gate, in the temperature range between 4 K and 300 K.
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| 6. |
- Muench, S., et al.
(författare)
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Time-resolved photoluminescence investigations on HfO2-capped InP nanowires
- 2010
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 21:10
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Tidskriftsartikel (refereegranskat)abstract
- We have employed time-resolved photoluminescence (PL) spectroscopy to study the impact of HfO2 surface capping by atomic layer deposition (ALD) on the optical properties of InP nanowires (NWs). The deposition of high-kappa dielectrics acting as a gate oxide is of particular interest in view of possible applications of semiconductor NWs in future wrap-gated field effect transistors (FETs). A high number of charged states at the NW-dielectrics interface can strongly degrade the performance of the FET which explains the strong interest in high quality deposition of high-kappa dielectrics. In the present work we show that time-resolved spectroscopy is a valuable and direct tool to monitor the surface quality of HfO2-capped InP NWs. In particular, we have studied the impact of ALD process parameters as well as surface treatment prior to the oxide capping on the NW-dielectrics interface quality. The best results in terms of the surface recombination velocity (S-0 = 9.5 x 10(3) cm s(-1)) were obtained for InP/GaP core/shell NWs in combination with a low temperature (100 degrees C) ALD process. While the present report focuses on the InP material system, our method of addressing the surface treatment for semiconductors with high-kappa dielectrics will also be applicable to nanoelectronic devices based on other III/V material systems such as InAs.
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| 7. |
- Schukfeh, M. I., et al.
(författare)
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Formation of nanogaps in InAs nanowires by selectively etching embedded InP segments
- 2014
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 25:46
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Tidskriftsartikel (refereegranskat)abstract
- We present a method to fabricate nanometer scale gaps within InAs nanowires by selectively etching InAs/InP heterostructure nanowires. We used vapor-liquid-solid grown InAs nanowires with embedded InP segments of 10-60 nm length and developed an etching recipe to selectively remove the InP segment. A photo-assisted wet etching process in a mixture of acetic acid and hydrobromic acid gave high selectivity, with accurate removal of InP segments down to 20 nm, leaving the InAs wire largely unattacked, as verified using scanning electron and transmission electron microscopy. The obtained nanogaps in InAs wires have potential as semiconducting electrodes to investigate electronic transport in nanoscale objects. We demonstrate this functionality by dielectrophoretically trapping 30 nm diameter gold nanoparticles into the gap.
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| 8. |
- Suyatin, Dmitry, et al.
(författare)
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Sulfur passivation for ohmic contact formation to InAs nanowires
- 2007
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 18:10
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the formation of ohmic contacts to InAs nanowires by chemical etching and passivation of the contact areas in an ammonium polysulfide, (NH4)(2)S-x, water solution. The nanowires were exposed to different dilution levels of the (NH4)(2)Sx solution before contact metal evaporation. A process based on a highly diluted ( NH4)S-2(x) solution was found to be self-terminating, with minimal etching of the InAs. The stability of the contacts was investigated with electrical measurements as a function of storage time in vacuum and air.
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| 9. |
- Thelander, Claes, et al.
(författare)
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AFM manipulation of carbon nanotubes: realization of ultra-fine nanoelectrodes
- 2002
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 13:1, s. 108-113
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the possibility of using carbon nanotubes as flexible, mobile electrical probes able to electrically contact nanometre- scaled objects. Configurations with metal electrodes evaporated on top of multi-, few- and single-wall carbon nanotubes have been studied. Scanning probe manipulation was used to create nano-mechanical switches by first cutting the various tubes, and then moving the parts back into electrical contact. We found multiwall tubes to be best suited as mobile probes, mainly due to their insensitivity to mechanical deformation. Finally, we present an example where the scanning probe manipulation technique has been used to electrically connect two carbon nanotubes to a 7 nm gold particle.
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| 10. |
- Thelander, Claes, et al.
(författare)
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The electrical and structural properties of n-type InAs nanowires grown from metal-organic precursors.
- 2010
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 21:20
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Tidskriftsartikel (refereegranskat)abstract
- The electrical and structural properties of 111B-oriented InAs nanowires grown using metal-organic precursors have been studied. On the basis of electrical measurements it was found that the trends in carbon incorporation are similar to those observed in the layer growth, where an increased As/In precursor ratio and growth temperature result in a decrease in carbon-related impurities. Our results also show that the effect of non-intentional carbon doping is weaker in InAs nanowires compared to bulk, which may be explained by lower carbon incorporation in the nanowire core. We determine that differences in crystal quality, here quantified as the stacking fault density, are not the primary cause for variations in resistivity of the material studied. The effects of some n-dopant precursors (S, Se, Si, Sn) on InAs nanowire morphology, crystal structure and resistivity were also investigated. All precursors result in n-doped nanowires, but high precursor flows of Si and Sn also lead to enhanced radial overgrowth. Use of the Se precursor increases the stacking fault density in wurtzite nanowires, ultimately at high flows leading to a zinc blende crystal structure with strong overgrowth and very low resistivity.
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