DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawing, the preferred embodiment of the invention relates to the production of solar cells from EFG grown P-type silicon ribbon.
For this embodiment, there is provided as a starting piece a partially finished cell 1.
Partially finished cell 1 has a substrate 2, preferably formed from a P-type conductivity silicon ribbon, one side (hereafter the "front side") of which has been provided with a relatively shallow junction 4 (i.
e.
, a junction of between about 3,000 and about 7,000 Angstrom units deep), an N-type conductivity region 6, and a mask 8.
Mask 8 is of a material (e.
g.
, a dielectric) to which metals, such as nickel, will only poorly adhere, and is configured to expose portions of the front surface of substrate 2 in a pattern of a multi-fingered grid electrode (e.
g.
, an electrode having the form illustrated in U.
S.
Pat.
No.
3,686,036).
The other side (hereafter the "rear side") of the substrate is preferably provided with a layer 10 of aluminum alloyed to the substrate and a P.
sup.
+ region 12.
The P.
sup.
+ region 12 preferably has a depth of from about 1 to about 5 microns.
Partially finished cell 1 may be fabricated by any of a number of means well known in the art.
For instance, junction 4 and region 6 may be formed in a P-type silicon substrate 2 by the diffusion of phosphorus, and mask 8 may be formed on the front surface thereof by photolithography or printing.
Thus, for instance, a layer of phosphosilicate glass, formed as detailed in U.
S.
Pat.
No, 4,152,824, may be used as a source for the phosphorous dopant, the glass layer then being appropriately masked and etched through in part using a buffered HF solution so as to form mask 8.
Layer 10 and P.
sup.
+ region 12 may be formed by coating the rear side of the substrate with a layer of an aluminum paste comprising aluminum powder in a volatile organic vehicle, such as terpineol, that can be removed by evaporation, and then heating the substrate to remove any volatile or pyrolyzable organic components of the paste and to alloy the aluminum to the substrate and form the P
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Semiconductor manufacture 
