| 1. |
- Balocco, C, et al.
(författare)
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Microwave detection at 110 GHz by nanowires with broken symmetry
- 2005
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 5:7, s. 1423-1427
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Tidskriftsartikel (refereegranskat)abstract
- By using arrays of nanowires with intentionally broken symmetry, we were able to detect microwaves up to 110 GHz at room temperature. This is, to the best of our knowledge, the highest speed that has been demonstrated in different types of novel electronic nanostructures to date. Our experiments showed a rather stable detection sensitivity over a broad frequency range from 100 MHz to 110 GHz. The novel working principle enabled the nanowires to detect microwaves efficiently without a dc bias. In principle, the need for only one high-resolution lithography step and the planar architecture allow an arbitrary number of nanowires to be made by folding a linear array as many times as required over a large area, for example, a whole wafer. Our experiment on 18 parallel nanowires showed a sensitivity of approximately 75 mV dc output/mW of nominal input power of the 110 GHz signal, even though only about 0.4% of the rf power was effectively applied to the structure because of an impedance mismatch. Because this array of nanowires operates simultaneously, low detection noise was achieved, allowing us to detect -25 dBm 110 GHz microwaves at zero bias with a standard setup.
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| 2. |
- Björk, Mikael, et al.
(författare)
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Tunable effective g factor in InAs nanowire quantum dots
- 2005
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 72:20
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Tidskriftsartikel (refereegranskat)abstract
- We report tunneling spectroscopy measurements of the Zeeman spin splitting in InAs few-electron quantum dots. The dots are formed between two InP barriers in InAs nanowires with a wurtzite crystal structure grown using chemical beam epitaxy. The values of the electron g factors of the first few electrons entering the dot are found to strongly depend on dot size. They range from close to the InAs bulk value in large dots vertical bar g(*)vertical bar=13 down to vertical bar g(*)vertical bar=2.3 for the smallest dots.
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| 3. |
- Dick Thelander, Kimberly, et al.
(författare)
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A new understanding of au-assisted growth of III-V semiconductor nanowires
- 2005
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Ingår i: Advanced Functional Materials. - : Wiley. - 1616-3028 .- 1616-301X. ; 15:10, s. 1603-1610
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Tidskriftsartikel (refereegranskat)abstract
- Semiconductor nanowires of III-V materials have generated much interest in recent years. However, the growth mechanisms by which these structures form are not well understood. The so-called vapor-liquid-solid (VLS) mechanism has often been proposed for III-V systems, with a chemically inert, liquid metal particle (typically Au) acting as a physical catalyst. We assert here that An is, in fact, not inert with respect to the semiconductor material but rather interacts with it to form a variety of intermetallic compounds. Moreover, we suggest that III-V nanowire growth can best be understood if the metallic particle is not a liquid, but a solid-phase solution or compound containing An and the group III material. The four materials GaP, GaAs, InP, and InAs will be considered, and growth behavior related to their particular temperature-dependent interaction with Au.
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| 4. |
- Dick Thelander, Kimberly, et al.
(författare)
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Failure of the vapor-liquid-solid mechanism in Au-assisted MOVPE growth of InAs nanowires
- 2005
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 5:4, s. 761-764
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Tidskriftsartikel (refereegranskat)abstract
- We report the temperature dependence of the Au-assisted growth of InAs nanowires in MOVPE. Extensive studies of the growth of such nanowires have attributed growth to the so-called vapor-liquid-solid (VLS) mechanism, with a liquid Au-In alloy particle. We assert here that growth is instead assisted by a solid particle and does not occur at all when the particle is a liquid. Thus the temperature range of InAs nanowire growth is limited by the melting of the Au-In alloy. Comparison with growth of InAs nanowires in the same system assisted by a layer of SiOx is used to support this conclusion.
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| 5. |
- Fasth, Carina, et al.
(författare)
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Tunable double quantum dots in InAs nanowires defined by local gate electrodes
- 2005
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 5:7, s. 1487-1490
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Tidskriftsartikel (refereegranskat)abstract
- We report on low-temperature transport measurements on single and double quantum dots defined using local gates to electrostatically deplete InAs nanowires grown by chemical beam epitaxy. This technique allows us to define multiple quantum dots along a semiconducting nanowire and tune the coupling between them.
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| 6. |
- Hansen, Adam, et al.
(författare)
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Spin relaxation in InAs nanowires studied by tunable weak antilocalization
- 2005
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. ; 71, s. 1-205328
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Tidskriftsartikel (refereegranskat)abstract
- We report on a low-temperature magnetoconductance study to characterize the electrical and spin transport properties of n-type InAs nanowires grown by chemical beam epitaxy. A gate-controlled crossover from weak localization to weak antilocalization is observed. The measured magnetoconductance data agrees well with theory for one-dimensional quasi-ballistic systems and yields a spin relaxation length which decreases with increasing gate voltage.
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| 7. |
- Johansson, Jonas, et al.
(författare)
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Mass transport model for semiconductor nanowire growth
- 2005
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 109:28, s. 13567-13571
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Tidskriftsartikel (refereegranskat)abstract
- We present a mass transport model based on surface diffusion for metal-particle-assisted nanowire growth. The model explains the common observation that for III/V materials thinner nanowires are longer than thicker ones. We have grown GaP nanowires by metal-organic vapor phase epitaxy and compared our model calculations with the experimental nanowire lengths and radii. Moreover, we demonstrate that the Gibbs-Thomson effect can be neglected for III/V nanowires grown at conventional temperatures and pressures.
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| 8. |
- Persson, Jonas, et al.
(författare)
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Strain effects on individual quantum dots: Dependence of cap layer thickness
- 2005
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 72:8
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the effects of strain on individual self-assembled quantum dots (QDs) exemplified by InP dots embedded in GaInP. The quantum dot sample was etched from the top and in this way the amount of capping material was reduced. In a sequence of etch cycles, the cap layer was thinned, and the photoluminescence from several individual QDs could be followed as a function of cap layer thickness. The evolution of the emission spectra clearly depended on the quantum dot size. We interpret this as arising from differences in the aspect ratio for quantum dots of different sizes. The influence of the capping layer, for different QD geometries, was modeled using deformation potential theory with the strain calculated using a full three-dimensional linear elasticity model. The results agree well with the experimental observations.
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| 9. |
- Pettersson, Håkan, et al.
(författare)
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Photocurrent spectroscopy on self-assembled InAs quantum dots embedded in InP
- 2005
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Ingår i: Microelectronics Journal. - Amsterdam : Elsevier. - 0026-2692. ; 36:3-6, s. 227-230
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we report on an overview of recent results from Fourier transform photocurrent (FTPC) measurements in the infrared spectral region on ensembles of self-assembled InAs quantum dots embedded in a matrix of InP. In interband PC, clear signals related to the dots are observed. Comparing the PC- and PL spectra, we observe that the fundamental transition is absent in the PC spectra, which we interpret in terms of Pauliblocking due to a filled electron ground state of the dots. Our results furthermore suggest that an Auger process is involved in forming the interband PC signal. In intersubband PC, peaks related to transitions from the dots' ground- and first excited states to the conduction band of the matrix are observed. Using a novel approach of combining FTPC with illumination from an additional external non-modulated light source, we have measured the spectral distribution of photoionization of excitons in quantum dots and found an exciton binding energy in good agreement with theoretical calculations.
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| 10. |
- Sköld, Niklas, et al.
(författare)
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Growth and optical properties of strained GaAs-GaxIn1-xP core-shell nanowires
- 2005
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 5:10, s. 1943-1947
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Tidskriftsartikel (refereegranskat)abstract
- We have synthesized GaAs-GaxIn1-xP (0.34 < x < 0.69) core-shell nanowires by metal-organic vapor phase epitaxy. The nanowire core was grown Au-catalyzed at a low temperature (450 degrees C) where only little growth takes place on the side facets. The shell was added by growth at a higher temperature (600 degrees C), where the kinetic hindrance of the side facet growth is overcome. Photoluminescence measurements on individual nanowires at 5 K showed that the emission efficiency increased by 2 to 3 orders of magnitude compared to uncapped samples. Strain effects on the band gap of lattice mismatched core-shell nanowires were studied and confirmed by calculations based on deformation potential theory.
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