| 1. |
- Borgström, Magnus, et al.
(författare)
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Arrays of Ge islands on Si(001) grown by means of electron-beam pre-patterning
- 2003
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484. ; 14:2, s. 264-267
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Tidskriftsartikel (refereegranskat)abstract
- We show that well-defined arrays of self-assembled Ge dots on Si(001) can be grown after pre-patterning the Si surface by means of an electron beam. The electron beam produces C-containing growth masks. The overgrowth of these masks with Si results in pits at the Si surface, in and around which Ge dots nucleate selectively. A manifold of different arrays can be obtained. Almost perfect arrays of quadruples of dots nucleate in the intersections of the four {11n} facets. This way of producing quantum dot arrays is very promising for producing dot structures suitable for use in the study of, for instance, dot-dot tunnelling and related effects.
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| 2. |
- Borgström, Magnus, et al.
(författare)
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Quadruples of Ge dots grown on patterned Si surfaces
- 2003
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 259:3, s. 262-266
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present the results of Ge deposition on a pre-pattemed Si surface. By partially overgrowing nanometer-sized electron beam-induced carbon deposits, faceted pits form at the Si surface and well-defined arrays of self-assembled Ge dots can be grown site selectively in and around those. Typically, four closely spaced Ge islands are formed by preferential nucleation around the pits. By varying the pattern of C-deposits a manifold of different arrays can be obtained. (C) 2003 Elsevier B.V. All rights reserved.
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| 3. |
- Borgström, Magnus, et al.
(författare)
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Site-controlled Ge quantum dot growth on Si by the use of electron beam pre-patterning
- 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
- By growth of Si on substrates that have been pre-patterned by electron-beam induced carbon nano-growth masks, nano-holes form at the Si surface. We have grown self-assembled Ge quantum dots in these holes by ultra high vacuum chemical vapour phase deposition (UHV-CVD). We usually find four dots in each hole. By varying the amount of deposited Ge, we can obtain either four dome-shaped or four pyramid-shaped dots in the majority of holes. These dot arrangements could be used for the realisation of the simplest functional cell for quantum-dot cellular automata (QCA)
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| 4. |
- Ghatnekar-Nilsson, Sara, et al.
(författare)
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A new multifunctional platform based on high-aspect ratio interdigitated NEMS structures
- 2009
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 20:17
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Tidskriftsartikel (refereegranskat)abstract
- A multifunctional NEMS platform based on a mass-producible, surface relief grating has been developed and fabricated directly in polymer materials. The pattern consists of high aspect ratio interdigitated nanometer-sized pairs of walls and can be produced in a low-complexity one-step patterning process with nanoimprint lithography. In this paper, we demonstrate the usefulness of the platform primarily by showing an application as a high-sensitivity mass sensor in air. The sensors, which are based on the high frequency resonant response of around 200 MHz, show a mass responsivity of the order of 0.1 Hz/zg per wall at room temperature and in ambient air. Their ability to selectively adsorb airborne target molecules, such as thiols, is also demonstrated. We also show that the same device can function as a varactor for electronic circuits based on its large tunable capacitive range.
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| 5. |
- 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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| 6. |
- Wernersson, Lars-Erik, et al.
(författare)
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A combined chemical vapor deposition and rapid thermal diffusion process for SiGe Esaki diodes by ultra-shallow junction formation
- 2005
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Ingår i: IEEE Transactions on Nanotechnology. - 1536-125X. ; 4:5, s. 594-598
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Tidskriftsartikel (refereegranskat)abstract
- SiGe Esaki diodes have been realized by rapid thermal diffusion of phosphorous into an SiGe layer grown by ultra-high-vacuum chemical-vapor-deposition on an Si p(+)-substrate for the first time. The phosphorous-doped SiGe forms the n(+)-electrode, while heavily boron-doped Si0.74Ge0.26 and Si substrate is used for the p(+) electrode. The diodes show a peak current density of 0.18 kA/cm(2), a current peak-to-valley ratio of 2.6 at room temperature, and they exhibit only a weak temperature dependence. Cross-sectional transmission microscopy showed a good crystalline quality of the strained Si0.74Ge0.26 layer even after the diffusion step at 900 degrees C.
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| 7. |
- Zela, Vilma
(författare)
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Ge quantum dots on Si
- 2004
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Ingår i: NSF/SSF Workshop on Nanoscience and Nanotechnology, Lund, Sweden (2004).
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Konferensbidrag (refereegranskat)
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| 8. |
- 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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| 9. |
- Zela, Vilma, et al.
(författare)
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Single-crystalline Ge grown epitaxially on oxidized and reduced Ge/Si(100) islands
- 2004
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 263:1-4, s. 90-93
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the Ge overgrowth of oxidized and reduced Ge/Si islands is studied. The islands were grown in a hotwall ultrahigh vacuum chemical vapour deposition reactor. The oxidation was performed in air at room temperature and the reduction in a hydrogen atmosphere at 600degreesC. After reduction, Ge was deposited at the same temperature. The results of the overgrowth show that the reduced native oxide on top of the islands transfers the epitaxial information from the Si substrate to the epitaxial layer, whereas no growth takes place outside the Ge islands. This makes it possible to use these islands as crystal seeds for epitaxial lateral overgrowth for growing Ge layers on top of Si substrates. (C) 2003 Elsevier B.V. All rights reserved.
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| 10. |
- Zela, Vilma
(författare)
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UHV-CVD growth of Ge/Si nanostructures
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is based on the results concerning the epitaxial growth and characterization of silicon (Si) and germanium (Ge) nanostructures. The growth technique was the Ultra High Vacuum Chemical Vapor Deposition (UHV-CVD) that works in relatively low temperatures and low growth pressures. The UHV-CVD chamber was also used for the reduction experiments. The work presented here involves three different projects: (i) Ge islands as crystal seeds for the growth of a pure Ge layer on Si(100); (ii) Positioning of Ge/Si islands using surface patterning and (iii); Growth of SiGe nanostructures for realization of Esaki Diodes. The goal of the first project (i) was to use self-assembled Ge islands as crystal seeds for growing a thick layer of pure Ge on Si substrate which is of a great technological importance. A two-step growth process was used to achieve an almost unimodal size distribution of Ge islands. The study of the surface included oxidation under different conditions (temperature, atmosphere) and reduction in hydrogen at different temperatures. Conditions were found where the islands were partially oxidized, leaving part of the islands intact. The reduction of the surface in hydrogen did not result in the complete recovery of the Ge islands as intended. Instead crystalline germanium segregations that were epitaxially oriented to the substrate were observed. Finally, the native oxide of the surface structure was used for the overgrowth with Ge. Single crystalline Ge could be grown over the islands. This was achieved by a oxidation/reduction step, before the growth on top of the Ge islands. The epitaxial information was transformed from the island through the reduced oxide layer to the deposited Ge. Atomic Force Microscope (AFM), Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) were used for characterization of the samples. The aim of the second project (ii) was the controlled spatial positioning of Ge islands that could be useful for different applications. The surface patterning was realized through the deposition of nanometer-sized carbon masks by an electron beam. Partial overgrowth of the masked surface with Si resulted in pits over the C depositions. Ge deposition on these structures occurred preferentially in this pits. By changing the size of the carbon growth mask, and thereby by changing the lateral extension of the pit, the number of the dots around the pit was altered. Quadruples of Ge islands could be grown. grown AFM was used for characterization while Electron Beam Lithography (EBL) for patterning of Si substrate. In the third project, a combination of UHV-CVD epitaxial growth of SiGe hetero-structures with Rapid Thermal Diffusion (RTD) process of Phosphorous was used to fabricate SiGe Esaki tunnel diodes. Heavily doped Boron SiGe layers followed by intrinsic SiGe layers were grown on p-doped Si substrates by UHV-CVD. Phosphorous was diffused through the intrinsic layer realizing the p-n junction. This combined approach is suitable for the integration of tunnel diodes with the mainstream SiGe-technology. The diodes show a peak current density of 0.18 kA/cm2 and a peak to valley ratio of 2.6 at room temperature.
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| 11. |
- 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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