| 1. |
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| 2. |
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| 3. |
- Axelson, Olav, 1937-, et al.
(författare)
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Regulatory toxicology and pharmacology.
- 2003
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Ingår i: International journal of occupational and environmental health. - 1077-3525 .- 2049-3967. ; 9, s. 386-389
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Tidskriftsartikel (refereegranskat)
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| 4. |
- Björk, Mikael, et al.
(författare)
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One-dimensional heterostructures in semiconductor nanowhiskers
- 2002
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 80:6, s. 1058-1060
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Tidskriftsartikel (refereegranskat)abstract
- We report on the growth of designed heterostructures placed within semiconductor nanowhiskers, exemplified by the InAs/InP material system. Based on transmission electron microscopy, we deduce the interfaces between InAs and InP to be atomically sharp. Electrical measurements of thermionic emission across an 80-nm-wide InP heterobarrier, positioned inside InAs whiskers 40 nm in diameter, yield a barrier height of 0.6 eV. On the basis of these results, we propose new branches of physics phenomena as well as new families of device structures that will now be possible to realize and explore.
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| 5. |
- Björk, Mikael, et al.
(författare)
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One-dimensional steeplechase for electrons realized
- 2002
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 2:2, s. 87-89
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Tidskriftsartikel (refereegranskat)abstract
- We report growth of one-dimensional semiconductor nanocrystals, nanowhiskers, in which segments of the whisker with different composition are formed, illustrated by InAs whiskers containing segments of InP. Our conditions for growth allow the formation of abrupt interfaces and heterostructure barriers of thickness from a few monolayers to 100s of nanometers, thus creating a one-dimensional landscape along which the electrons move. The crystalline perfection, the quality of the interfaces, and the variation in the lattice constant are demonstrated by high-resolution transmission electron microscopy, and the conduction band off-set of 0.6 eV is deduced from the current due to thermal excitation of electrons over an InP barrier.
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| 6. |
- Borgström, Magnus, et al.
(författare)
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Site control of InAs quantum dots on a patterned InP surface: As/P exchange reactions
- 2003
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Ingår i: Journal of Crystal Growth. - 0022-0248. ; 248, s. 310-316
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Tidskriftsartikel (refereegranskat)abstract
- In this paper. we present the effect of annealing temperature and annealing time on InAs site-controlled quantum dot growth. Individual InAs quantum dots formed by self-assembling have been positioned into holes, created by partial overgrowth of electron beam induced nano-carbon deposits by metal organic vapor phase epitaxy. As/P exchange reactions produce material sufficient for selective dot nucleation in the holes. Results. showing that As/P exchange reactions occur even when capping the dots with InP are presented. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 7. |
- Borgström, Magnus, et al.
(författare)
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Site-control of InAs quantum dots on a patterned InP surface: As/P exchange reactions
- 2002
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Ingår i: 7th International Conference on Nanometer-Scale Science and Technology and 21st European Conference on Surface Science.
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Konferensbidrag (refereegranskat)abstract
- We present the effect of annealing temperature and annealing time on InAs/InP site-controlled quantum dot growth. Electron beam pre-patterning forms carbon nano-deposits at the InP surface, which then can be used as growth masks to form nano-holes at the surface. By only annealing of the patterned InP surface under an arsine ambient, As/P exchange reactions produce material sufficient for selective dot nucleation in the holes at the surface
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| 8. |
- Bryllert, Tomas, et al.
(författare)
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Designed emitter states in resonant tunneling through quantum dots
- 2002
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 80:15, s. 2681-2683
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Tidskriftsartikel (refereegranskat)abstract
- Resonant tunneling through a single layer of self-assembled quantum dots (QDs) is compared to tunneling through two layers of vertically aligned (stacked) dots. The difference can be viewed as going from a two-dimensional emitter to a zero-dimensional emitter. The temperature dependence of current peaks originating in tunneling through individual QDs and individual stacks is used to clarify this point. In addition, we show that the statistical size distribution of self-assembled quantum dots causing the inhomogeneous broadening in luminescence experiments can be analyzed in a resonant tunneling experiment. (C) 2002 American Institute of Physics.
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| 9. |
- Bryllert, Tomas, et al.
(författare)
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Resonant tunneling through coupled self-assembled quantum dots and the influence of inhomogeneous broadening
- 2002
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Ingår i: 7th International Conference on Nanometer-Scale Science and Technology and 21st European Conference on Surface Science.
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Konferensbidrag (refereegranskat)abstract
- Resonant tunneling through a single layer of self-assembled quantum dots (QDs) as well as tunneling through two layers of vertically aligned (stacked) dots is investigated. The difference between single and double layers of QDs can be viewed as going from a two-dimensional emitter to a zero-dimensional emitter. By fabricating small-area devices we are able to probe single stacks of quantum dots, revealing details of the coupling between the stacked dots. Very sharp resonances, with peak-to-valley ratios of several hundred, have been measured in the current-voltage characteristics. We also show that the statistical size distribution of self-assembled quantum dots causing the inhomogeneous broadening in luminescence experiments can be analysed in a resonant tunneling experiment
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| 10. |
- Håkanson, Ulf, et al.
(författare)
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Luminescence polarization of ordered GaInP/InP islands
- 2003
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 82:4, s. 627-629
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Tidskriftsartikel (refereegranskat)abstract
- The luminescence polarization properties of GaInP islands have been investigated. The islands, which form during overgrowth of InP quantum dots, were studied using scanning tunneling luminescence (STL) and photoluminescence (PL). STL from these islands shows emission at an energy below the main emission peak of the bulk GaInP. The linear PL polarization anisotropy was measured at low temperature, for which the emission from the islands shows high polarization anisotropy. The intensity maximum for the emission occurs for light polarized parallel to the elongation of the islands. The observed linear PL polarization anisotropy indicates the presence of highly ordered domains of GaInP in the islands. (C) 2003 American Institute of Physics.
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| 11. |
- Håkanson, Ulf, et al.
(författare)
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Photon mapping of single quantum dots by scanning tunneling microscopy induced luminescence spectroscopy
- 2002
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Ingår i: 7th International Conference on Nanometer-Scale Science and Technology and 21st European Conference on Surface Science.
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Konferensbidrag (refereegranskat)abstract
- Scanning tunneling microscopy induced luminescence (STML) has been used to investigate individual self-assembled InP quantum dots overgrown with GaInP. We will present results correlating the surface morphology with the optical properties of single dots. In particular, the strain induced energy-shift of the dot emission with increasing cap layer thickness and its relation to the overgrowth will be discussed. Effects of the dots on the properties of the overgrown GaInP will also be treated. STML spectra and monochromatic photon maps are compared with results from photoluminescence and transmission electron microscopy measurements. Furthermore, a comparison with theoretical calculations is made
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| 12. |
- Håkanson, Ulf, et al.
(författare)
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Quantum-dot-induced ordering in GaxIn1-xP/InP islands
- 2002
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 66:23
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Tidskriftsartikel (refereegranskat)abstract
- Thin layers of GaxIn1-xP grown on top of self-assembled InP quantum dots has been studied using transmission electron microscopy (TEM), scanning tunneling microscopy (STM), and low-temperature scanning tunneling luminescence (STL). STM reveals that the overgrowth is highly uneven, in which elongated GaxIn1-xP islands covering the dots are formed. TEM and high-spatial-resolution STL show that the quantum dots locally induce domains with higher degree of ordering in the islands. The luminescence from these domains is observed as a strong GaxIn1-xP peak at an energy below the emission from the GaxIn1-xP barrier material.
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| 13. |
- Johansson, Mikael, et al.
(författare)
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Correlation between overgrowth morphology and optical properties of single self-assembled InP quantum dots
- 2003
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 68:12
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the early stages of GaInP overgrowth on InP quantum dots (QD's) experimentally and theoretically. A direct correlation between the surface morphology and the optical properties of individual InP QD's is made using scanning tunneling microscopy (STM) and scanning tunneling luminescence. The geometric structure of the islands is further investigated using cross-sectional transmission electron microscopy (TEM). The overgrowth occurs in three stages; initially the InP QD's act as seeding points for the overgrowth, where the GaInP grows laterally from the side facets of the QD. The growth occurs preferentially in the [110] direction and elongated GaInP/InP islands are formed. As the overgrowth continues the islands increase laterally in size and GaInP also starts to grow between the islands, but not covering the top of the InP QD's. The growth of GaInP on top of the QD's commences once the islands have begun to coalesce. Using a model based on the STM and TEM results the electronic structures of the QD's have been calculated by eight-band k.p theory. The calculations are in good agreement with the experimental results. Our findings unravel the details of the strain induced energy shift of the QD luminescence previously reported [Pistol , Appl. Phys. Lett. 67, 1438 (1995)].
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| 14. |
- Ohlsson, Jonas, et al.
(författare)
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Comparision between (111)B and (100) III-V nanowhiskers
- 2002
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Ingår i: 7th International Conference on Nanometer-Scale Science and Technology and 21st European Conference on Surface Science.
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Konferensbidrag (refereegranskat)abstract
- Epitaxial III-V nanowhiskers have been grown with orientation in the [111]B and [100] directions. While the nature of the crystal structure in the (111)B type of whiskers varies more or less at random between hexagonal (wurtzite) and cubic (zincblende) structure, the (100) type whiskers are of single crystal zincblende structure. We show that the bounding surface facets of the whiskers are either {110} type (zincblende) or the related {1120} facets (wurtzite), giving a rectangular cross-section of (100) whiskers and a hexagonal cross section of (111)B whiskers. The variations in crystal structure and facet type are discussed in connection to the electronic properties of the whiskers and the choice of whisker type for applications in electronics and photonics
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| 15. |
- Persson, Ann, et al.
(författare)
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Heterointerfaces in III-V semiconductor nanowhiskers
- 2002
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Ingår i: Conference Proceedings - International Conference on Indium Phosphide and Related Materials. - 1092-8669. ; , s. 281-283
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Konferensbidrag (refereegranskat)abstract
- We have investigated heterostructures formed within Vapor-Liquid-Solid grown III-V nanowhiskers. The growth conditions that are typical for chemical beam epitaxy facilitate the creation of atomically abrupt interfaces. In this paper we investigate the properties of heterostructure interfaces including switching of either the column-V material (As, P) or the column-III material (In, Ga).
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| 16. |
- Sass, T, et al.
(författare)
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Oxidation and reduction behavior of Ge/Si islands
- 2002
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 81:18, s. 3455-3457
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the oxidation/reduction behavior of dome-shaped three-dimensional islands of Ge on Si(001) grown by ultrabigh vacuum chemical vapor deposition. The oxidation was done by exposing the surfaces to H2O steam in N-2. The reduction was done by H-2, which selectively reduces only the GeO2. The results of the oxidation/reduction processes under varying conditions were analyzed by high-resolution transmission electron microscopy. We found that the selective reduction of such structures does not result in a perfect recovery of the former Ge dots, but results in phase-segregated Ge enrichments. In many cases these enrichments show epitaxial relationship with the underlying Si substrate. These structures are of potential interest for Ge dots embedded in an insulating material as, well as for lateral epitaxial overgrowth of SiO2 / Si(001) by Ge, using the reduced Ge dots as the seeds for epitaxy.
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| 17. |
- Sass, T, et al.
(författare)
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Strain in GaP/GaAs and GaAs/GaP resonant tunnelling heterostructures
- 2003
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Ingår i: Journal of Crystal Growth. - 0022-0248. ; 248, s. 375-379
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Tidskriftsartikel (refereegranskat)abstract
- We studied the morphology of GaP/(001)GaAs and GaAs/(001)GaP heterostructures grown by metal-organic vapour-phase epitaxy and found wire-like surface undulations elongated in the [110] direction. We attribute this elongation to anisotropic lateral growth rates in the [110] and [110] directions, which are due to a different roughness of monolayer surface steps. In III-V materials grown by molecular beam epitaxy. such surface corrugations are usually elongated in [110]. We explain this difference by the two growth methods having inverted ratios of lateral growth rates in [110] and [110]. Resonant tunnelling diodes fabricated from the GaP/GaAs heterostructures showed very symmetric I-V characteristics. Their peak-to-valley ratio was limited to 2. most probably due to the corrugation of the GaP barriers. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 18. |
- Thelander, Claes, et al.
(författare)
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Heterostructures incorporated in one-dimensional semiconductor materials and devices
- 2003
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Ingår i: Physics and Semiconductors 2002 : Proceedings of the 26th International Conference on the Physics of Semiconductors. - 0750309245 ; 171, s. 253-260
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- As an alternative to traditional top-down techniques for fabrication of one-dimensional devices we here report an approach wherein a bottom-up technique is used to create one-dimensional device structures. We use the vapor-liquid-solid growth method, in which a catalytically active gold nanoparticle forms a eutectic alloy with the nanowire constituents. Our method of growth allows atomically abrupt interfaces between different III-V semiconductors, also for highly mismatched combinations for which conventional growth techniques can not be used. Special emphasis is put on the processing of ohmic contacts to nanowires. We describe the transport properties of nanowires containing heterostructures from which band off-sets between two different binary materials are determined. Finally, we report the creation of double-barrier resonant tunneling diodes in which a single InAs quantum dot surrounded by InP tunnel barriers acts as the active element in the device, resulting in energetically sharp resonant tunneling peaks reflecting tunneling into zero-dimensional states of the quantum dot.
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| 19. |
- Wernersson, Lars-Erik, et al.
(författare)
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Metalorganic vapor phase epitaxy-grown GaP/GaAs/GaP and GaAsP/GaAs/GaAsP n-type resonant tunnelling diodes
- 2002
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 80:10, s. 1841-1843
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Tidskriftsartikel (refereegranskat)abstract
- We have studied GaP/GaAs/GaP and GaAsxP1-x/GaAs/GaAsxP1-x double-barrier resonant tunnelling diodes grown by metalorganic vapor phase epitaxy. We find that GaP tensile strained barriers in GaP/GaAs/GaP diodes may be grown with a barrier thickness below the critical thickness of about 12 monolayers. However, a corrugation of the strained barrier is observed by transmission electron microscopy. This variation may explain the low peak-to-valley ratio of the diodes (about 2). In contrast, GaAsxP1-x/GaAs/GaAsxP1-x resonant tunnelling diodes have been grown with a homogeneous thickness of the barriers, consequently showing a substantially improved electrical performance compared to the GaP diodes with peak-to-valley ratios >5.
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| 20. |
- Wernersson, Lars-Erik, et al.
(författare)
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Thin layers of GaInP, GaP and GaAsP in metalorganic vapour phase epitaxy-grown resonant tunnelling diodes
- 2002
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Ingår i: Applied Surface Science. - 1873-5584. ; 190:1, s. 252-257
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the epitaxial growth and electrical performance of Al-free, GaAs-based, resonant tunnelling diodes (RTDs) including thin barriers of GaInP, GO, or GaAsxP1-x. n-Type tunnelling diodes have been fabricated and the symmetry in the current-voltage (I-V) characteristics, as well as the peak-to-valley ratios, are found to be sensitive probes for the inter-face quality in the heterostructures. For GaInP RTDs, we show that the introduction of Gap intermediate layers is crucial for the realisation. of a useful tunnelling current. RTDs including thin barriers (less than about 10 monolayers (ML)) of Gap are realised, but the strong mismatch between the materials limit the useful thickness. Finally, RTDs with GaAslambdaP1-x alloys are fabricated showing the best peak-to-valley ratio of the diodes (about 5), as well as a symmetric I-V characteristics. The electrical data are further compared to studies by transmission electron microscopy (TEM) in the various material systems.
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| 21. |
- Zela, Vilma, et al.
(författare)
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Oxidation and reduction behaviour of Ge/Si islands
- 2002
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Ingår i: 7th International Conference on Nanometer-Scale Science and Technology and 21st European Conference on Surface Science.
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Konferensbidrag (refereegranskat)abstract
- We have investigated the oxidation/reduction behaviour of dome-shaped three-dimensional islands of Ge on Si(001) grown by UHV-CVD at 620°C. The oxidation was done by exposing the surfaces to a steam of H2O in N2. The reduction was done in H2, which at T<800 °C selectively reduces GeO2 only. The results of the oxidation/reduction processes under varying conditions were analyzed by high-resolution transmission electron microscopy. We found that the selective reduction of such structures does not result in a perfect recovery of the former Ge dots, but results in phase-segregated Ge-enrichments. In most cases, these enrichments show epitaxial relationship to the underlying Si substrate. These structures are therefore of potential interest for lateral epitaxial overgrowth of the SiO2 by Ge, using the reduced Ge dots as the seeds for epitaxy
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| 22. |
- Zela, Vilma, et al.
(författare)
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Unimodal dome-shaped island population of Ge/Si (001) by step-wise growth in UHV-CVD
- 2002
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Ingår i: Physica E: Low-Dimensional Systems and Nanostructures. - 1386-9477. ; 13:2-4, s. 1013-1017
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Tidskriftsartikel (refereegranskat)abstract
- This work introduces a new approach to achieve a unimodal dome-shaped island population for the self-assembled Ge/Si (0 0 1) dots grown by ultra-high vacuum chemical vapour deposition at T = 620 degreesC. A step-wise growth mode is applied, consisting of two Ge deposition steps with a short growth interruption in between. In the first step, a "base structure" with pyramids and domes is grown while in the second one, an additional Ge amount at reduced pressure is supplied. Selective "feeding" of only the pyramids and their conversion into domes occurs. Atomic force microscopy and transmission electron microscopy studies indicate that the shape transition starts with nucleation of material onto the {105} facets close to the most strain-relaxed top area of the pyramids.
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