Silicon Thick 4 slab
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Thick 4" slab.
I thought this was a thick slab cut from a silicon crystal boule, just like the many wafers you see described here only thicker. But if you look at the surface you can clearly see that there are many different randomly oriented crystal facets. Because silicon boules used for making wafers are always grown as a single huge perfect crystal, this slab can't have come from one. Which makes me curious to know why else someone would want to make a circular silicon slab, if not for making chips.
Turns out the application is in making solar cells. I'm told such multi-crystal ingots are made by a directional solidification casting system, which sounds a lot like continuous casting to me (a method used for creating long ingots in which new liquid is poured into one end of a long mold even as solid ingot is coming out the other end).
Source: eBay seller eureka52
Contributor: Theodore Gray
Acquired: 10 August, 2004
Text Updated: 8 April, 2008
Price: $8
Size: 4"
Purity: 99.9%