| 1. |
- Arnberg, Lars, et al.
(författare)
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Solvent refining of silicon for solar cells –some practical aspects
- 2020
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Ingår i: Journal of Crystal Growth. - : Elsevier B.V.. - 0022-0248 .- 1873-5002. ; 531
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Tidskriftsartikel (refereegranskat)abstract
- Solvent refinement has been suggested as an energy- and cost-efficient process to produce high purity silicon for photovoltaic solar cells. In this process, metallurgical grade silicon is dissolved in a liquid metal e.g. Al at high temperature. High purity silicon crystals can then be precipitated by decreasing the temperature and extracted from the melt. Residual aluminium is then removed by leaching, and after remelting and directional solidification, the purified silicon can be used as silicon for solar cells. Metallurgical grade silicon (99 wt%Si) with iron as the main impurity has been dissolved to 40 wt% in liquid aluminium at 1000 °C. Silicon crystals have been extracted slightly above the eutectic temperature. The crystals have then been leached in 10% hydrochloric acid at room temperature. Silicon crystal have been sorted into three size fraction which have been melted separately and thereafter analyzed by light optical- and electron microscopy with EDS analysis. After leaching, extracted material has been remelted together with silicon oxide in order to oxidize residual aluminium. The extracted material contains significant amounts of residual Al-Si eutectic. The aluminium has not been removed completely by the leaching and insoluble metal rich intermetallic compounds have been found in the smallest size fraction. The residual aluminium can be further reduced by oxidation by silicon oxide and sedimentation of the aluminium oxide.
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| 2. |
- Cardenas, Edgar, et al.
(författare)
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Microstructural evolution of condensed aggregates during the crystallization of ZSM-5 from a heterogeneous system
- 2021
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Ingår i: Journal of Crystal Growth. - : Elsevier. - 0022-0248 .- 1873-5002. ; 568–569
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Tidskriftsartikel (refereegranskat)abstract
- The microstructural evolution of precursors of ZSM-5 zeolite crystallized from a heterogeneous system using fumed silica, sodium aluminate and tetrapropylammonium ions as reagents is investigated. Entities previously described by Ren et al. (Chem. Mater. 2012, 24, 10, 1726–1737) as condensed aggregates, were extensively studied using scanning electron microscopy, and energy dispersive spectroscopy. It was observed that the condensed aggregates first comprise a core of nanocrystals that is enveloped by a shell of amorphous gel phase. During crystallization, the amorphous shell surrounding the core is converted into ZSM-5 crystals that grow to a film surrounding the core. The crystals in the film grow competitively with nutrients provided by the liquid phase from the surroundings, while the nanocrystals in the core show little or no signs of growth.
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| 3. |
- Nakahata, Hidetoshi, et al.
(författare)
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Investigation of halide vapor phase epitaxy of In2O3 on sapphire (0001) substrates
- 2021
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Ingår i: Journal of Crystal Growth. - : ELSEVIER. - 0022-0248 .- 1873-5002. ; 563
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the growth conditions on halide vapor phase epitaxy of In2O3 on sapphire (0 0 0 1) substrates was investigated. Only the most thermally stable phase c-In2O3 grows at growth temperatures of 400 to 1000 degrees C. The growth rate increased as the growth temperature increased up to 700 degrees C, and layers with rough surfaces and a preferred (100) orientation were grown. Above 700 degrees C, the growth rate became constant, the preferential orientation changed to (111), and layers with smooth surfaces were grown. At 1000 degrees C, the volume fraction of the (111)-oriented domains in the grown layer reached 99.0%, although there were in-plane twins rotated by 180 degrees. The growth rate also increased as the input partial pressure of the InCl or O-2 source gas was increased, and a high growth rate exceeding 10 mu m/h was found. The layer grown at 1000 degrees C was of high purity and incorporated no impurities other than Cl. Optical transmission measurements of this layer showed high optical transmittance at energies below the optical gap of 3.47 eV.
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| 4. |
- Seredynski, B., et al.
(författare)
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Molecular beam epitaxy growth of MoTe2 on hexagonal boron nitride
- 2022
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Ingår i: Journal of Crystal Growth. - : Elsevier. - 0022-0248 .- 1873-5002. ; 596
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Tidskriftsartikel (refereegranskat)abstract
- Hexagonal boron nitride has already been proven to serve as a decent substrate for high quality epitaxial growth of several 2D materials, such as graphene, MoSe2, MoS2 or WSe2. Here, we present for the first time the molecular beam epitaxy growth of MoTe2 on atomically smooth hexagonal boron nitride (hBN) substrate. Occurrence of MoTe2 in various crystalline phases such as distorted octahedral 1T' phase with semimetal properties or hexagonal 2H phase with semiconducting properties opens a possibility of realization of crystal -phase homostructures with tunable properties. Atomic force microscopy studies of MoTe2 grown in a single monolayer regime enable us to observe impact of growth conditions on formation of various structures: flat grains, net of one-dimensional structures, quasi continuous monolayers with bilayer contribution. Comparison of the distribution of the thickness with Poisson distribution shows that tested growth conditions favorite formation of grains with monolayer thickness. The diffusion constant of MoTe2 grown on hBN can reach order of 10-6 cm2/s for typical growth conditions. Raman spectroscopy results suggest a coexistence of various phases with domination of 2H MoTe2 for samples grown at lower temperatures. XPS measurements confirm the stoichiometry of MoTe2.
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| 5. |
- Strömberg, Axel, et al.
(författare)
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Heteroepitaxy of GaAsP and GaP on GaAs and Si by low pressure hydride vapor phase epitaxy
- 2020
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Ingår i: Journal of Crystal Growth. - : ELSEVIER. - 0022-0248 .- 1873-5002. ; 540
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Tidskriftsartikel (refereegranskat)abstract
- Direct heteroepitaxy of GaAsP and GaP on GaAs and on Si by low-pressure hydride vapor phase epitaxy (HVPE) is investigated as prior studies for photovoltaics and non-linear optics applications. When growing GaAsP on GaAs, it is found that the ambient gas during substrate pre-heating influences the ternary composition as well as the crystalline quality of the subsequent growth. GaAs0.72P0.28 with bandgap energy of 1.76 eV has been achieved, which would be suitable for a top cell in Si tandem solar cell structures. Growth of GaP was investigated on planar GaAs as a prior study for realizing orientation patterned (OP) GaP on OP-GaAs. Threading dislocations caused by the 3.6% lattice mismatch between GaP and GaAs are suppressed by adjusting the GaCl flow, achieving a low full width at half maximum of 146 arcsec for the X-ray diffraction omega scan. Direct heteroepitaxy of GaAsP on Si aiming for achieving a GaAsP/Si dual junction solar cell is demonstrated. The inherent problem of initiating nucleation during the direct heteroepitaxy of III-V on Si by HVPE is overcome by utilizing the vapor mixing approach to grow a low-temperature GaP buffer layer on Si, followed by a GaAsP layer grown by conventional HVPE.
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| 6. |
- Tan, Xiaoqin, et al.
(författare)
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Band gap tailoring in a low toxicity and low-cost solar cell absorber Cu3SbS4 through Na alloying : A first-principles study
- 2023
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 607
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Tidskriftsartikel (refereegranskat)abstract
- High power conversion efficiency, high stability, low cost, and environmentally friendly manufacturing are the main requirements for a commercializable photovoltaic device. Cu3SbS4 is an eco-friendly and earth-abundant compound that is studied as a potential solar cell absorber. However, its band gap is smaller than the ideal value. In this work, the possibility to modulate and improve the band gap by sodium alloying has been investigated by means of the first-principles density functional theory with the HSE06 hybrid functional. Our results demonstrate that the Cu3-xNaxSbS4 alloy with a high alloying concentration should be possible to realize, and that the Na incorporation widens the gap. An alloy concentration of x approximate to 0.64 yields the desired gap for a solar light absorber, which can then lead to a more efficient solar cell.
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| 7. |
- Tran, Dat, et al.
(författare)
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Self-catalyst growth and characterization of wurtzite GaAs/InAs core/ shell nanowires
- 2021
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Ingår i: Journal of Crystal Growth. - : ELSEVIER. - 0022-0248 .- 1873-5002. ; 564
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Tidskriftsartikel (refereegranskat)abstract
- Research on nanowire (NW) growth of III-V semiconductors including GaAs and InAs demonstrated the ability to grow in both wurtzite (WZ) and zincblende (ZB) polymorphs. However, the control of crystal phase in selfcatalyzed NW growth is still a remaining challenge. In this study we report a controlled growth of GaAs/InAs core/shell nanowires in WZ phase using self-catalyzed molecular beam epitaxy (MBE). The GaAs NWs having pure WZ crystal were achieved and attributed to the effect of small wetting angle, which is realized by supplying high V/III ratio. Furthermore, the WZ formation is shown to be uninfluenced by NW diameter. For the wetting angle larger than 90?, mixed phase starts to be observed. The InAs shell is planarly grown on six m-plane facets of the GaAs core NWs leading to the same strain states along a and c axes of growth plane, in which tensile and compressive strains are observed for GaAs core and InAs shell, respectively. High-resolution transmission electron microscopy (HR-TEM) reveals a few misfit dislocations (-0.03 nm- 1) at GaAs/InAs interface indicating insignificant strain relief via creating misfit dislocation. Electrical characterization of the hetero-wires shows that the InAs shell exhibits n-type conduction. A room-temperature sheet carrier concentration at zero gate-bias of 2.5 ? 1012 cm-2 and the corresponding carrier mobility of - 900 cm2 V-1 s- 1 are demonstrated.
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| 8. |
- Wang, Hongzhen, et al.
(författare)
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Effects of substrate temperature on the uniformity of InGaAs epilayers using a dual-zone manipulator
- 2021
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 574
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Tidskriftsartikel (refereegranskat)abstract
- Three-inch InGaAs epilayers are grown by solid source molecular beam epitaxy using the manipulator equipped with dual-zone heaters. The effects of the substrate temperature on the uniformity of material surface morphology, indium composition, photoluminescence, electronic mobility, and background doping are investigated. As the temperature of the outer heater in the range of 625 °C to 655 °C, no dim area is observed on the edge of the material surface. At the same time, the indium composition fluctuation of the high-resolution X-ray diffraction and the photoluminescence wavelength fluctuation are less than ±0.1% for the epilayers grown at the optimum substrate temperatures.
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