| 1. |
- Borschel, Christian, et al.
(författare)
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A New Route toward Semiconductor Nanospintronics : Highly Mn-Doped GaAs Nanowires Realized by Ion-Implantation under Dynamic Annealing Conditions
- 2011
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Ingår i: Nano letters (Print). - Washington : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 11:9, s. 3935-3940
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Tidskriftsartikel (refereegranskat)abstract
- We report on highly Mn-doped GaAs nanowires (NWs) of high crystalline quality fabricated by ion beam implantation, a technique that allows doping concentrations beyond the equilibrium solubility limit. We studied two approaches for the preparation of Mn-doped GaAs NWs: First, ion implantation at room temperature with subsequent annealing resulted in polycrystalline NWs and phase segregation of MnAs and GaAs. The second approach was ion implantation at elevated temperatures. In this case, the single-crystallinity of the GaAs NWs was maintained, and crystalline, highly Mn-doped GaAs NWs were obtained. The electrical resistance of such NWs dropped with increasing temperature (activation energy about 70 meV). Corresponding magnetoresistance measurements showed a decrease at low temperatures, indicating paramagnetism. Our findings suggest possibilities for future applications where dense arrays of GaMnAs nanowires may be used as a new kind of magnetic material system.
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| 2. |
- Conache, Gabriela, et al.
(författare)
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Bias-controlled friction of InAs nanowires on a silicon nitride layer studied by atomic force microscopy
- 2010
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Ingår i: Physical Review B Condensed Matter. - College Park, Md. : American Physical Society. - 0163-1829 .- 1095-3795. ; 82:3
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Tidskriftsartikel (refereegranskat)abstract
- By studying how nanowires lying on a surface bend when pushed by an atomic force microscopy tip we are able to measure the friction between them and the substrate. Here, we show how the friction between InAs nanowires and an insulating silicon nitride layer varies when a dc voltage is applied to the tip during manipulation. The bias charges the capacitor formed by the wire and the grounded silicon back contact. Electrostatic forces increase the contact pressure and allow us to tune the friction between the wire and the silicon nitride surface. Using nanowires of about 40-70 nm diameter and a few microns in length we have applied biases in the range +12 to -12 V. A monotonic increase of the sliding friction with voltage was observed. This increase in friction with the normal force implies that the mesoscopic nanowire-surface system behaves like a macroscopic contact, despite the nanometer size of the contact in the direction of motion. The demonstrated bias-controlled friction has potential applications in MEMS/NEMS devices.
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| 3. |
- Conache, Gabriela, et al.
(författare)
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Comparative friction measurements of InAs nanowires on three substrates
- 2010
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Ingår i: Journal of Applied Physics. - College Park, MD : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 108:9
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated friction between InAs nanowires and three different substrates: SiO2, fluorosilanized SiO2, and Si3N4. The nanowires were pushed laterally with the tip of an atomic force microscope and the friction force per unit length for both static and sliding friction was deduced from the equilibrium shape of the bent wires. On all three substrates, thick wires showed a difference between sliding and static friction of up to three orders of magnitude. Furthermore, all substrates display a transition to stick-slip motion for nanowires with a diameter of less than about 40 nm. Hydrophobic and hydrophilic substrates display similar friction behavior suggesting that a condensed water layer does not strongly influence our results. The patterns and trends in the friction data are similar for all three substrates, which indicates that they are more fundamental in character and not specific to a single substrate. ©2010 American Institute of Physics.
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| 4. |
- Höglund, Linda, 1974-, et al.
(författare)
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Energy level scheme of InAs/InxGa1-xAs/GaAs quantum-dots-in-a-well infrared photodetector structures
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - Woodbury, NY : American Physical Society. - 1098-0121 .- 1550-235X. ; 82:3, s. 035314-
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Tidskriftsartikel (refereegranskat)abstract
- A thorough investigation of quantum-dots-in-a-well structures for infrared photodetector applications has been performed employing different experimental techniques. The electronic structure of self-assembled InAs quantum dots embedded in an In0.15Ga0.85As/GaAs quantum well (QW) was deduced from photoluminescence (PL) and PL excitation (PLE) spectroscopy. From polarization-dependent PL it was revealed that the quantum dots hold two electron energy levels and two heavy-hole levels. Tunnel capacitance spectroscopy confirmed an electron energy level separation of about 50 meV, and additionally, that the conduction-band ground state and excited state of the dots are twofold and fourfold degenerates, respectively. Intersubband photocurrent spectroscopy, combined with simultaneous interband pumping of the dots, revealed a dominant transition at 150 meV (8.5 mu m) between the ground state of the quantum dots and the excited state of the QW. Results from detailed full three-dimensional calculations of the electronic structure, including effects of composition intermixing and interdot interactions, confirm the experimentally unravelled energy level scheme of the dots and well.
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| 5. |
- Shang, X. -J, et al.
(författare)
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Quantum-dot-induced optical transition enhancement in InAs quantum-dot-embedded p-i-n GaAs solar cells
- 2011
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Ingår i: Applied Physics Letters. - New York, N.Y. : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 99:11, s. 113514-113514-3
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Tidskriftsartikel (refereegranskat)abstract
- Photocurrents (PCs) of three p–i–n GaAs solar cells, sample A with InAs quantum dots (QDs) embedded in the depletion region, B with QDs in the n region, and C without QDs, were studied experimentally and theoretically. Above GaAs bandgap, the PC of A is increased, while B is decreased with respect to C, since in A, the QD-induced reflection of hole wave function increases its overlap with electron wave function so that the optical transition rate is enhanced, while carrier mobility in B is reduced due to QD-induced potential variations. Moreover, A and B have increased PCs in the sub-GaAs-bandgap range due to QD optical absorptions.
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| 6. |
- Suyatin, Dmitry, et al.
(författare)
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Nano-Schottky contacts realized by bottom-up technique
- 2010
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Ingår i: INEC 2010 - 2010 3rd International Nanoelectronics Conference, Proceedings. - Piscataway, N.J. : IEEE Press. - 9781424435432 ; , s. 252-253
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Konferensbidrag (refereegranskat)abstract
- Properties of nanostructures realized by bottom-up techniques are often different from their bulk counterparts. Here we present a study of a nano-Schottky contact formed at the interface between a gold catalytic particle and an epitaxially grown GaxIn1-xAs/InAs nanowire. Selective electrical connections formed to the catalytic particle on one side and to the InAs segment on the other side allowed electrical and optical characterization of the formed junction. We demonstrate that the heterostructure region adjacent to the catalytic particle may act as an ultra-small volume unipolar photodetector with potentially ultra-fast response.
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