Crystallographic Analysis of a Bulky Polycrystalline Silicon Used for Photovoltaic Conversion

An analysis of the crystallographic orientation of polycristalline silicon ingots, obtained by a directional solidification in carbon crucible according to Bridgman method using no seed crystal, is described. The grain growth, in alignment with the higher temperature gradient, produces different crystallized zones in the ingot : an axially columnar structure in the middle and a radial dentritic structure on the edges. At first the usual methods of X-ray diffraction by reflection are used (back reflection Laue photographs, Debye-Scherrer method). The neutron diffraction by transmission was used to complete the precedent results. The preferred orientations vary in the different parts of the ingot : [211] and [111] orientations in the middle, [111], and [331] orientations on the edges. Lattice constant deviations (s15.10"4 A) have been observed between the different crystalline zones. These previous rafined methods take a long time over controls in an industrial elaboration. Therefore an electrochemical method using the anodic dissolution of silicon has been developped. The deposit thus obtained was investigated by X-ray diffraction and S.I.M.S. ; a correlation between the film thickness and the reticular density of the etched surface was obtained. So the solidification texture can be shown, without a great precision but very rapidly by a coloured card with interference colours of the thin anodic layer. This method suits well control of an industrial preparation. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982143