A thin layer of single-crystal silicon is produced by forming first trenches in a silicon substrate having (111) orientation; forming narrower second trenches at the bases of the trenches; anisotropically etching lateral channels (4) from the second trenches, until adjacent etch fronts (16) substantially meet; and detaching said layer from the substrate. The trenches may be arranged so that the resultant layer has rows of slots, whit the slots in adjacent rows being mutually offset. Solar cells may be formed on strips (5) between the trenches, having lengths of more than 50 mm, widths of up to 5 mm, and thicknesses of less than 100 microns, and having two electrical contacts on the same face (6) of each strip (5).

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> Method of producing crystalline semiconductor material and method of fabricating semiconductor device

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