| 1. |
- Hjort, Martin, et al.
(författare)
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Doping profile of InP nanowires directly imaged by photoemission electron microscopy
- 2011
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 99:23
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Tidskriftsartikel (refereegranskat)abstract
- InP nanowires (NWs) with differently doped segments were studied with nanoscale resolution using synchrotron based photoemission electron microscopy. We clearly resolved axially stacked n-type and undoped segments of the NWs without the need of additional processing or contacting. The lengths and relative doping levels of different NW segments as well as space charge regions were determined indicating memory effects of sulfur during growth. The surface chemistry of the nanowires was monitored simultaneously, showing that in the present case, the doping contrast was independent of the presence or absence of a native oxide. (C) 2011 American Institute of Physics. [doi:10.1063/1.3662933]
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| 2. |
- Hjort, Martin, et al.
(författare)
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Surface Chemistry, Structure, and Electronic Properties from Microns to the Atomic Scale of Axially Doped Semiconductor Nanowires.
- 2012
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851.
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Tidskriftsartikel (refereegranskat)abstract
- Using both synchrotron-based photoemission electron microscopy/spectroscopy and scanning tunneling microscopy/spectroscopy, we obtain a complete picture of the surface composition, morphology, and electronic structure of InP nanowires. Characterization is done at all relevant length scales from micrometer to nanometer. We investigate nanowire surfaces with native oxide and molecular adsorbates resulting from exposure to ambient air. Atomic hydrogen exposure at elevated temperatures which leads to the removal of surface oxides while leaving the crystalline part of the wire intact was also studied. We show how surface chemical composition will seriously influence nanowire electronic properties. However, opposite to, for example, Ge nanowires, water or sulfur molecules adsorbed on the exterior oxidized surfaces are of less relevance. Instead, it is the final few atomic layers of the oxide which plays the most significant role by strongly negatively doping the surface. The InP nanowires in air are rather insensitive to their chemical surroundings in contrast to what is often assumed for nanowires. Our measurements allow us to draw a complete energy diagram depicting both band gap and differences in electron affinity across an axial nanowire p-n junction. Our findings thus give a robust set of quantitative values relating surface chemical composition to specific electronic properties highly relevant for simulating the performance of nanoscale devices.
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| 3. |
- Jain, Vishal, 1989-, et al.
(författare)
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Large area photodetectors based on InP NWs with InAs/InAsP QWs
- 2014
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Konferensbidrag (refereegranskat)abstract
- Focal plane arrays have a widespread use in infrared imaging, which often rely on cryogenic cooling to curtail the dark current level necessary for a reasonable signal-to-noise ratio. Quantum well (QW) infrared photodetectors are uniform over large areas, but suffer from a severe drawback related to the selection rules for intersubband absorption. An interesting alternative is self-assembled III-V nanowires offering a key advantage owing to the enhanced absorption by optical resonance effects and strain relaxation.We present electrical and optical results from large ensembles of n+-i-n+ InP NWs, axially grown on InP substrates with InAs/InAsP QWs embedded within the i-segment, designed for both interband and intersubband detection. The NWs are contacted in a vertical geometry using 50 nm SiO2 as the insulating layer and ITO as the top contact. We first investigate the crystal quality of the InAsP QWs grown in 180 nm diameter NWs, using PL, CL and TEM. To achieve more abrupt InAs/InAsP QWs, we grow 130 nm diameter NWs and deplete the In present in the Au catalysts. The effect of n-doping on the device performance is studied by fabricating two different NW geometries, with and without an n+-segment grown before the nominal i-segment in the NW. In addition, the position of the QWs within the i-segment is varied to further scrutinize effects related to doping and crystal structure. Finally, we report spectrally resolved photocurrent results from the QWs in the near-infrared region and discuss about the further developments needed for intersubband detection.
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| 4. |
- Timm, Rainer, et al.
(författare)
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Current−Voltage Characterization of Individual As-Grown Nanowires Using a Scanning Tunneling Microscope
- 2013
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 13:11, s. 5182-5189
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Tidskriftsartikel (refereegranskat)abstract
- Utilizing semiconductor nanowires for (opto)- electronics requires exact knowledge of their current−voltage properties. We report accurate on-top imaging and I−V characterization of individual as-grown nanowires, using a subnanometer resolution scanning tunneling microscope with no need for additional microscopy tools, thus allowing versatile application. We form Ohmic contacts to InP and InAs nanowires without any sample processing, followed by quantitative measurements of diameter dependent I−V properties with a very small spread in measured values compared to standard techniques.
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| 5. |
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| 6. |
- Troian, Andrea, et al.
(författare)
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Nanobeam X-ray Fluorescence Dopant Mapping Reveals Dynamics of in Situ Zn-Doping in Nanowires
- 2018
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; , s. 6461-6468
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Tidskriftsartikel (refereegranskat)abstract
- The properties of semiconductors can be controlled using doping, making it essential for electronic and optoelectronic devices. However, with shrinking device sizes it becomes increasingly difficult to quantify doping with sufficient sensitivity and spatial resolution. Here, we demonstrate how X-ray fluorescence mapping with a nanofocused beam, nano-XRF, can quantify Zn doping within in situ doped III-V nanowires, by using large area detectors and high-efficiency focusing optics. The spatial resolution is defined by the focus size to 50 nm. The detection limit of 7 ppm (2.8 × 1017 cm-3), corresponding to about 150 Zn atoms in the probed volume, is bound by a background signal. In solar cell InP nanowires with a p-i-n doping profile, we use nano-XRF to observe an unintentional Zn doping of 5 × 1017 cm-3 in the middle segment. We investigated the dynamics of in situ Zn doping in a dedicated multisegment nanowire, revealing significantly sharper gradients after turning the Zn source off than after turning the source on. Nano-XRF could be used for quantitative mapping of a wide range of dopants in many types of nanostructures.
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| 7. |
- Wallentin, Jesper, et al.
(författare)
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Degenerate p-doping of InP nanowires for large area tunnel diodes
- 2011
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 99:25
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated p-doping of InP nanowires using diethyl zinc. Two-terminal devices showed non-linear source-drain characteristics and p-type gate dependence. Electron beam induced current measurements were employed to determine minority carrier diffusion lengths. We used large-area tunnel diodes to demonstrate degenerate doping, showing peak current densities of up to 0.11 A/cm(2) and room temperature peak to valley current ratios of 5.3. These results demonstrate that high p- and n-doping, paired with sharp doping profiles, can be achieved in InP nanowires. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3669697]
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