Silicon-on ceramic process. Silicon sheet growth and device development for the large-area silicon sheet and cell development tasks of the low-cost solar array project. Quarterly report No. 12, April 2, 1979-June 29, 1979 Page: 50 of 70
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We conclude that this analysis, which is still preliminary, is consistent with grain
boundaries in our SOC cells having infinite surface recombination velocity. Further
studies and modeling will be conducted to verify this conclusion and consider the implica-
tion of these results for solar cell performance.
GROWTH MODELING (S. B. Schuldt)
The growth of sheet silicon or silicon ribbon from the melt can happen, in principle,
in either of two modes, as illustrated in Figure 18. In the conventional mode (a), the
liquid-solid interface (LSI) is oriented approximately perpendicular to the pull direction.
The latent heat of fusion released at the LSI is carried in the pull direction and must be
disposed of by radiation and convection to the relatively cool environment of the solid
ribbon. The word "symmetric" fits this mode because of the plane of symmetry through
the half-thickness points. The other mode (b) lacks a plane of symmetry, as diagrammed
here, and may be called "asymmetric." Because the LSI is inclined at a small angle, 0,
to the pull direction, most of the latent heat of fusion is eliminated immediately by cross-
ing transversely to the free solid surface. Only a small fraction of the latent heat remains
to be disposed of downstream (upwards as represented in Figure 18 from the solidifica-
tion wedge. It is debatable whether asymmetric growth has ever been successfully demon-
strated, but it is a critically important technology to pursue theoretically and experimentally.
It is inherently much faster than symmetric growth and may have other advantages such as
entrapment of impurities.
SOLID
-*y
J
LIQUID
(a)
SOLID
LIQUID
Figure 18. Silicon Ribbon Growth in (a) Symmetric and (b)
Asymmetric Modes, The letters v and t are pull
speed and ribbon thickness, respectively.
40
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Chapman, P.W.; Zook, J.D.; Heaps, J.D.; Grung, B.L.; Koepke, B. & Schuldt, S.B. Silicon-on ceramic process. Silicon sheet growth and device development for the large-area silicon sheet and cell development tasks of the low-cost solar array project. Quarterly report No. 12, April 2, 1979-June 29, 1979, report, July 31, 1979; United States. (https://digital.library.unt.edu/ark:/67531/metadc1065830/m1/50/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.