both sides with silicon layers (Fig. 8). Therefore, the ribbon coming up from the growth chamber is a composite structure with the carbon substrate embedded between two silicon layers. After growth, the substrate is burned in oxygen at high temperature, which releases unsupported silicon sheets. The originality of the RAD process, in the large family of ribbon vertical growth methods, is in the use of an ‘internal shaper', wettable enough by molten silicon to support the freezing meniscus. Two straightforward consequences follow from this concept. First, it permits a free rise of the freezing meniscus from the melt level to the line of attachment at the solid-liquid interface; this makes growth less dependent on melt temperature and virtually eliminates large flatness deviations typical of ribbon growth from a confined
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