Grain growth behaviors at a crystal/melt interface of multi-crystalline silicon are introduced in this article. It will be explained how the understanding of this phenomena has been progressed to ...date. The experimental results by in situ observations will be presented. The importance of growth kinetics at a grain boundary groove on the grain growth behavior will be shown.
Twin boundary formation at grain boundaries in multicrystalline Si during directional solidification was investigated by in situ observation of the crystal/melt interface. It was clearly shown that a ...twin boundary was formed on the {111} facet of grain-boundary groove at the crystal/melt interface. The large amount of undercooling in the melt at grain-boundary grooves promoted rapid crystallization and twin boundary formation.
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The top surface of a crystal–melt interface was observed directly during directional solidification of polycrystalline GaSb at a constant cooling rate, and the effect of {111}Σ3 twin boundary ...formation on the rate of grain growth parallel to the 〈111〉 direction was investigated. A {111}Σ3 twin boundary was generated by the decomposition of another {111}Σ3 twin boundary with formation of a Σ9 grain boundary. The growth of the crystal–melt interface in the direction parallel to the B direction was stalled during the nucleation and propagation of the new {111}Σ3 twin boundary. The growth rate of the crystal–melt interface after twin formation was approximately half of that before. This is considered to be due to {111} polarity reversal by twinning. The dangling bond density on the {111}A plane of GaSb is almost ten times of that on the {111}B plane, and the dangling bond density is related to the attachment energy of atoms of the plane; therefore, the growth rate in the A direction would be significantly lower than that in the B direction. These results indicate different growth rates in opposite 〈111〉 directions and a significant effect of the polarity on the competition of grain growth during the directional solidification of polycrystalline GaSb.
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It is imperative to improve the crystal quality of Si multicrystal ingots grown by casting because they are widely used for solar cells in the present and will probably expand their use in the ...future. Fine control of macro- and microstructures, grain size, grain orientation, grain boundaries, dislocation/subgrain boundaries, and impurities, in a Si multicrystal ingot, is therefore necessary. Understanding crystal growth mechanisms in melt growth processes is thus crucial for developing a good technology for producing high-quality Si multicrystal ingots for solar cells. In this review, crystal growth mechanisms involving the morphological transformation of the crystal-melt interface, grain boundary formation, parallel-twin formation, and faceted dendrite growth are discussed on the basis of the experimental results of in situ observations.
Eutectic growth of Ni-Si alloy with a composition of Ni44Si56 was observed in situ during directional solidification. Lamellar structure was evident behind the solidifying interface, which indicates ...that the two intermetallic phases, NiSi and NiSi2, generated a regular eutectic. The lamellae spacing was approximately 9.8 μm at a growth rate of 149.6 μm s−1. The phase boundaries migrated rapidly during the cooling stage and the lamellae enlarged significantly, which suggests that the lamellae spacing measured after the solidification may not be accurate for obtaining the relationship between the growth rate and the lamellae spacing. The in situ observation provides a promising way to obtain the exact eutectic spacing of Ni-Si eutectics.
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A fundamental understanding of crystal growth dynamics during directional solidification of multicrystalline Si (mc-Si) is crucial for the development of crystal growth technology for mc-Si ingots ...for use in solar cells.
observation of the crystal/melt interface is a way to obtain direct evidence of phenomena that occur at a moving crystal/melt interface during growth. In this review, some of the phenomena occurring in the solidification processes of mc-Si are introduced based on our
observation experiments, after a brief introduction of the history of the development of crystal growth technologies to obtain mc-Si ingots for solar cells.
•Facet formation during solidification of pure Sb was directly observed.•The faceted solid–liquid interface of pure Sb is bounded by {11¯02}•Mullins-Sekerka instability was not identified on the ...Sb{11¯02}•The α factor in the Jackson model does not explicitly predict the growth form.
In contrast to metals and semiconductors, few studies have focused on the faceting behavior of semimetals, and the atomic configuration of the solid–liquid interface is still incompletely understood. In this study, to obtain insight into the growth dynamics of semimetals, we directly observed solid–liquid interfaces during directional solidification of pure antimony. Morphological transformation of the solid–liquid interface depends on the direction of solidification: a zig-zag shaped solid–liquid interface is formed after the onset of instability in the direction of solidification normal to {312¯925}, while a curved interface becomes planar and no zig-zag facet formation is identified in the direction of solidification normal to {811¯324}. By combining in-situ observation and ex-situ electron-backscattered diffraction techniques, we showed that zig-zag shaped faces formed after the onset of instability at the solid–liquid interface are bounded by equivalent {11¯02} planes. The fact that the slowest growth kinetics occurs on the {11¯02} plane was also confirmed by measuring the growth velocity of the solid–liquid interface and the rate of temperature decrease in an observation furnace. Calculations based on thermal diffusion equations show that the Mullins-Sekerka instability does not occur on the {11¯02} plane, indicating that the growing {11¯02} plane at the solid–liquid interface is faceted.
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