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| 2. |
- Bolinsson, Jessica, et al.
(author)
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Diffusion length measurements in axial and radial heterostructured nanowires using cathodoluminescence
- 2011
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In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 315:1, s. 138-142
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Conference paper (peer-reviewed)abstract
- We have measured the ambipolar diffusion lengths in nanowires with GaAs and AlGaAs core material using cathodoluminescence imaging. This was done by combining III-V semiconductor materials with different bandgaps in single nanowires. We show that it is possible to record intensity profiles of the emission from segments of lower bandgap material positioned along the nanowire length and in this way gain an insight on important carrier transport properties of the nanowire core material. We present diffusion data for GaAs and AlGaAs nanowire core material in different radially and axially heterostructured nanowires and show that the diffusion of carriers is greatly increased by capping the nanowires with a higher-bandgap material. In addition, we show how a decoupling of the radial and axial growth during particle-seeded growth is necessary in order to reach long diffusion lengths along the core of axially heterostructured nanowires. In addition, for ternary compounds (InGaAs and AlGaAs), we observe compositional differences for radial and axial nanowire growth. (C) 2010 Elsevier B.V. All rights reserved.
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| 3. |
- Bolinsson, Jessica, et al.
(author)
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GaAs/AlGaAs heterostructure nanowires studied by cathodoluminescence
- 2014
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In: Nano Reseach. - : Springer Science and Business Media LLC. - 1998-0124 .- 1998-0000. ; 7:4, s. 473-490
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Journal article (peer-reviewed)abstract
- In this report we explore the structural and optical properties of GaAs/AlGaAs heterostructure nanowires grown by metalorganic vapour phase epitaxy using gold seed-particles. The optical studies were done by low-temperature cathodoluminescence (CL) in a scanning electron microscope (SEM). We perform a systematic investigation of how the nanowire growth-temperature affects the total photon emission, and variations in the emission energy and intensity along the length of the nanowires. The morphology and crystal structures of the nanowires were investigated using SEM and transmission electron microscopy (TEM). In order to correlate specific photon emission characteristics with variations in the nanowire crystal structure directly, TEM and spatially resolved CL measurements were performed on the same individual nanowires. We found that the main emission energy was located at around 1.48 eV, and that the emission intensity was greatly enhanced when increasing the GaAs nanowire core growth temperature. The data strongly suggests that this emission energy is related to rotational twins in the GaAs nanowire core. Our measurements also show that radial overgrowth by GaAs on the GaAs nanowire core can have a deteriorating effect on the optical quality of the nanowires. Finally, we conclude that an in situ pre-growth annealing step at a sufficiently high temperature significantly improves the optical quality of the nanowires.
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| 4. |
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| 5. |
- Bolinsson, Jessica
(author)
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The Crystal Structure of III-V Semiconductor Nanowires: Growth and Characterization
- 2010
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Doctoral thesis (other academic/artistic)abstract
- This thesis concerns growth and characterization of gold-particle seeded nanowires of III-V semiconductor materials (III-V NWs). The nanowires were grown using metal-organic vapour phase epitaxy (MOVPE) and characterized by various microscopy techniques. In particular cross-sectional scanning tunnelling microscopy (XSTM) and cathodoluminescence microscopy (CL) were employed to investigate heterostructured nanowires. In addition, the formation of the crystal structure within the nanowires as an effect of growth conditions was investigated by transmission electron microscopy. This thesis first presents an extensive description of the crystal structure and phases which have been observed in III-V NWs. It then gives an overview of the main characterization methods that were used in the included papers. Another part that is included concerns epitaxial growth in general and MOVPE in particular. The last part of the thesis is an outlook in which some important questions and possible future directions are presented and discussed. The basis for this thesis is 9 appended papers: Paper I-II present results from XSTM investigations; papers III-IV and VIII-IX concerns investigations of how to control the crystal phases and the density of defects within III-V NWs; paper V present a study of the effect of gold-particle fabrication method and deposition method on MOVPE growth of GaAs NWs; papers VI-VII present measurements of the ambipolar diffusion length in III-V NWs using cathodoluminescence.
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| 6. |
- Bolinsson, Jessica, et al.
(author)
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Wurtzite-zincblende superlattices in InAs nanowires using a supply interruption method.
- 2011
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In: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 22:26
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Journal article (peer-reviewed)abstract
- Crystal phase control in single III-V semiconductor nanowires has emerged recently as an important challenge and possible complement to conventional bandgap engineering in single material systems. Here we investigate a supply interruption method for precise crystal phase control in single nanowires. The nanowires are grown by metalorganic vapor phase epitaxy using gold particles as seeds and are analyzed by transmission electron microscopy. It is observed that wurtzite segments with controlled length and position can be inserted on demand into a pure InAs zincblende nanowire. The interface between wurtzite and zincblende segments can be made atomically sharp and the segments can be made only a few bilayers in thickness. The growth mechanisms, applicability and limitations of the technique are presented and discussed.
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| 7. |
- Caroff, Philippe, et al.
(author)
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Crystal Phases in III-V Nanowires: From Random Toward Engineered Polytypism
- 2011
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In: IEEE Journal of Selected Topics in Quantum Electronics. - 1077-260X. ; 17:4, s. 829-846
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Journal article (peer-reviewed)abstract
- III-V nanowires (NWs) are promising for a wide range of applications, ranging from optics to electronics, energy, and biological sensing. The structural quality of NWs is of paramount importance for the performance of such future NW-based devices. Random structural defects and polytypism occur naturally in semiconductor NWs, but progress both on the theoretical understanding and experimental control have been achieved recently. Here, we review progress towards the realization of perfect wurtzite and zinc-blende phases in III-VNWs, eventually leading to true phase engineering in single NWs.
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| 8. |
- Dick Thelander, Kimberly, et al.
(author)
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Control of III-V nanowire crystal structure by growth parameter tuning
- 2010
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In: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 25:2
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Journal article (peer-reviewed)abstract
- In this work we investigate the variation of the crystal structure of gold-seeded III-V nanowires with growth parameters, in order to gain a cohesive understanding of these effects. We investigate six III-V materials: GaAs, InAs, GaP, InP, GaSb and InSb, over a variation of growth conditions. All six of these materials exhibit a cubic zinc blende structure in bulk, but twin planes and stacking faults, as well as a hexagonal wurtzite structure, are commonly observed in nanowires. Parameters which may affect the crystal structure include growth temperature and pressure, precursor molar fraction and V/III ratio, nanowire diameter and surface density, and impurity atoms. We will focus on temperature, precursor molar fraction and V/III ratio. Our observations are compared to previous reports in the literature of the III-V nanowire crystal structure, and interpreted in terms of existing models. We propose that changes in the crystal structure with growth parameters are directly related to changes in the stable side facets.
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| 9. |
- Dick Thelander, Kimberly, et al.
(author)
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Controlling the Abruptness of Axial Heterojunctions in III-V Nanowires: Beyond the Reservoir Effect
- 2012
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In: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 12:6, s. 3200-3206
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Journal article (peer-reviewed)abstract
- Heterostructure nanowires have many potential applications due to the avoidance of interface defects by lateral strain relaxation. However, most heterostructure semiconductor nanowires suffer from persistent interface compositional grading, normally attributed to the dissolution of growth species in the common alloy seed particles. Although progress has been made for some material systems, most binary material combinations remain problematic due to the interaction of growth species in the alloy. In this work we investigate the formation of interfaces in InAs-GaAs heterostructures experimentally and theoretically and demonstrate a technique to attain substantially sharper interfaces. We show that by pulsing the Ga source during heterojunction formation, In is pushed out before GaAs growth initiates, greatly reducing In carry-over. This procedure will be directly applicable to any nanowire system with finite nonideal solubility of growth species in the alloy seed particle and greatly improve the applicability of these structures in future devices.
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