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- Ahrenby, Hanna, 1978-
(författare)
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Värdegrundsarbete i bildundervisning : en studie om iscensättning av policy i grundskolans senare år
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The overall purpose of this thesis is to describe and discuss preconditions for the enactment and the construction of fundamental values in art education in secondary school. The study is based on ethnographic methods, including classroom observations, video recordings and interviews with art teachers and pupils. Three art teachers and 36 pupils in grade eight and nine (age 14-16) have participated in the study. The schools are located in areas of different socio-economic status. Besides interviews, the empirical material consists of observation notes, video and sound recordings, documents and photographs from the observed lessons. In total, 27 lessons were observed and recorded, 20 interviews with teachers and seven interviews with pupils were conducted. The empirical material is analysed with a combination of policy enactment theory (Ball et al. 2012) and concepts form Bernstein (2000, 2003) and Bakhtin (1981, 1986).The analysis reveals that the conditions for policy enactment are created by several factors that interact. It is impossible to designate a single factor to explain why the enacted curriculum turns out the way it does. The contextual dimensions, such as material context, situated context, professional culture and external context (Ball et al. 2012), constitute a complex and unique contextual mix in every school. Together with existing subject traditions and teaching practices in art education, the unique contextual mix creates the conditions for enacting the fundamental values in art education.The art subject carries a tradition of image-making that pushes more theoretical syllabus content,such as image analysis, aside. The situated context influences the professional culture and, therefore,they function as a lens for selecting and translating the curriculum. Regardless of teachers' intentionsto enact the fundamental values in art education, the external context can create obstacles. The goal and result management of school leads to a focus on measurable subject knowledge and drive awayother curriculum parts such as the fundamental values, making it challenging to work with fundamental values in Art education.In conclusion, there are no prerequisites for realising the intentions of the fundamental values as expressed in the curriculum. Despite this, the fundamental values have a given place in Art education. Although, it is not always expressed verbally; instead, it is image-borne.
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- Bi, Zhaoxia, et al.
(författare)
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High In-content InGaN nano-pyramids : Tuning crystal homogeneity by optimized nucleation of GaN seeds
- 2018
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 123:2
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Tidskriftsartikel (refereegranskat)abstract
- Uniform arrays of submicron hexagonal InGaN pyramids with high morphological and material homogeneity, reaching an indium composition of 20%, are presented in this work. The pyramids were grown by selective area metal-organic vapor phase epitaxy and nucleated from small openings in a SiN mask. The growth selectivity was accurately controlled with diffusion lengths of the gallium and indium species, more than 1 μm on the SiN surface. High material homogeneity of the pyramids was achieved by inserting a precisely formed GaN pyramidal seed prior to InGaN growth, leading to the growth of well-shaped InGaN pyramids delimited by six equivalent 10 1 ̄ 1 facets. Further analysis reveals a variation in the indium composition to be mediated by competing InGaN growth on two types of crystal planes, 10 1 ̄ 1 and (0001). Typically, the InGaN growth on 10 1 ̄ 1 planes is much slower than on the (0001) plane. The formation of the (0001) plane and the growth of InGaN on it were found to be dependent on the morphology of the GaN seeds. We propose growth of InGaN pyramids seeded by 10 1 ̄ 1-faceted GaN pyramids as a mean to avoid InGaN material grown on the otherwise formed (0001) plane, leading to a significant reduction of variations in the indium composition in the InGaN pyramids. The InGaN pyramids in this work can be used as a high-quality template for optoelectronic devices having indium-rich active layers, with a potential of reaching green, yellow, and red emissions for LEDs.
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- Bi, Zhaoxia, et al.
(författare)
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InGaN Platelets : Synthesis and Applications toward Green and Red Light-Emitting Diodes
- 2019
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Ingår i: Nano Letters. - : American Chemical Society. - 1530-6984 .- 1530-6992. ; 19:5, s. 2832-2839
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we present a method to synthesize arrays of hexagonal InGaN submicrometer platelets with a top c-plane area having an extension of a few hundred nanometers by selective area metal-organic vapor-phase epitaxy. The InGaN platelets were made by in situ annealing of InGaN pyramids, whereby InGaN from the pyramid apex was thermally etched away, leaving a c-plane surface, while the inclined {101Ì1} planes of the pyramids were intact. The as-formed c-planes, which are rough with islands of a few tens of nanometers, can be flattened with InGaN regrowth, showing single bilayer steps and high-quality optical properties (full width at half-maximum of photoluminescence at room temperature: 107 meV for In 0.09 Ga 0.91 N and 151 meV for In 0.18 Ga 0.82 N). Such platelets offer surfaces having relaxed lattice constants, thus enabling shifting the quantum well emission from blue (as when grown on GaN) to green and red. For single InGaN quantum wells grown on the c-plane of such InGaN platelets, a sharp interface between the quantum well and the barriers was observed. The emission energy from the quantum well, grown under the same conditions, was shifted from 2.17 eV on In 0.09 Ga 0.91 N platelets to 1.95 eV on In 0.18 Ga 0.82 N platelets as a result of a thicker quantum well and a reduced indium pulling effect on In 0.18 Ga 0.82 N platelets. On the basis of this method, prototype light-emitting diodes were demonstrated with green emission on In 0.09 Ga 0.91 N platelets and red emission on In 0.18 Ga 0.82 N platelets.
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- Colvin, Jovana, et al.
(författare)
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Surface and dislocation investigation of planar GaN formed by crystal reformation of nanowire arrays
- 2019
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Ingår i: Physical Review Materials. - : American Physical Society. - 2475-9953. ; 3:9
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present a process of forming monolithic GaN surface from an ordered nanowire array by means of material redistribution. This process, referred to as reformation, is performed in a conventional MOVPE crystal growth system with the gallium supply turned off and allows a crystal nanostructure to change shape according to differences in surface energies between its facets. Using reformation, coalescence may proceed closer to thermodynamic equilibrium, which is required for fabrication of high-quality substrate material. Scanning probe techniques are utilized, complemented by cathodoluminescence and electron microscopy, to investigate structural and electrical properties of the surface after reformation, as well as to assess densities, location, and formation of different types of defects in the GaN film. Spatial variations in material properties such as intrinsic majority-carrier types can be attributed to the radical changes in growth conditions required for sequential transition between nanowire growth, selective shell growth, and reformation. These properties enable us to assess the impact of the process on densities, locations, and formation of different types of dislocations in the GaN film. We find a fraction of the nanowires to comprise of a single electrically neutral edge dislocation, propagating from the GaN buffer, while electrically active dislocations are found at coalesced interfaces between nanowires. By decreasing the mask aperture size and changing the nucleation conditions the prevalence of nanowires comprising edge dislocation was significantly reduced from 6% to 3%, while the density of interface dislocations was reduced from 6×108 to 4×107cm-2. Using a sequential reformation process was found to create inversion domains with low surface potential N-polar regions in an otherwise Ga-polar GaN film. The inversion domains were associated with pinned dislocation pairs, and were further confirmed by selective wet etching in NaOH. This lateral polarity inversion was thoroughly eliminated in samples formed by a continuous reformation process. These results reveal a path and challenges for growing GaN substrates of superior crystal quality through nanowire reformation.
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- Delgado Carrascon, Rosalia, et al.
(författare)
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Optimization of GaN Nanowires Reformation Process by Metalorganic Chemical Vapor Deposition for Device-Quality GaN Templates
- 2020
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Ingår i: Physica Status Solidi (B) Basic Research. - : Wiley. - 0370-1972 .- 1521-3951. ; 257:4
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Tidskriftsartikel (refereegranskat)abstract
- Herein, the potential of reformed GaN nanowires (NWs) fabricated by metalorganic chemical vapor deposition (MOCVD) for device-quality low-defect density templates and low-cost alternative to bulk GaN substrates is demonstrated. The effects of epilayer thickness and NW reformation conditions on the crystalline quality and thermal conductivity of the subsequent GaN epilayers are investigated. Smooth surfaces with atomically step-like morphologies with no spirals are achieved for GaN epilayers on the reformed NW templates, indicating step-flow growth mode. It is further found that annealing of the NWs at a temperature of 1030 °C in the presence of NH3 and H2, followed by a coalescence done at the same temperature under planar growth conditions, leads to the most efficient screw dislocation density reduction by nearly an order of magnitude. At these optimized conditions, the growth takes place in a layer-by-layer fashion, producing a smooth surface with a root mean square (RMS) roughness of 0.12 nm. The highest thermal conductivity of k = 206 W m−1 K−1, approaching the respective value of bulk GaN, is obtained for the optimized 2 μm-thick GaN layer. The thermal conductivity results are further discussed in terms of the phonon-dislocation and the phonon-boundary scattering.
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- Haggren, Tuomas, et al.
(författare)
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InP nanowire p-type doping via Zinc indiffusion
- 2016
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 451, s. 18-26
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Tidskriftsartikel (refereegranskat)abstract
- We report an alternative pathway for p-type InP nanowire (NW) doping by diffusion of Zn species from the gas phase. The diffusion of Zn was performed in a MOVPE reactor at 350–500 °C for 5–20 min with either H2 environment or additional phosphorus in the atmosphere. In addition, Zn3P2 shells were studied as protective caps during post-diffusion annealing. This post-diffusion annealing was performed to outdiffuse and activate Zn in interstitial locations. The characterization methods included photoluminescence and single NW conductivity and carrier concentration measurements. The acquired carrier concentrations were in the order of >1017 cm−3 for NWs without post-annealing, and up to 1018 cm−3 for NWs annealed with the Zn3P2 shells. The diffused Zn caused redshift to the photoluminescence signal, and the degree of redshift depended on the diffusion process.
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