James Meyer wrote:
On Sat, 04 Jun 2005 09:47:36 GMT, Matt Giwer
wroth:

Asad wrote:

HI,

How can I perform doping of silicon manually?

You can't.

I remember that back in the late 50's that Bell Labs was distributing
science project kits to schools to promote education. Remember that this was
back when the US was playing catch-up to the Russians.

One of the lits was put together to allow school kids to make silicon
solar cells right in the classroom with ordinary stuff found there. The kit
included silicon wafer slices, some chemicals, a 115 volt heating element
similar to the ones used in small radiant room heaters, some asbestos sheets for
insulation, some fine carbide sandpaper, and a list of instructions.

You built an oven from the heater and the asbestos sheets. The heater
was a ceramic cylinder with nichrome wire coiled around the outside and an
Edison screw base. The inside of the cylinder was open and you broke the
silicon wafer into pieces small enough to fit inside.

The wafer pieces were dipped into a water slurry of the chemical, I
forget exactly which chemical (probably something with phosphorous in it), and
placed in the heater/oven to get red hot. The original wafer pieces were
probably grown with an N or P dopant and the subsequent difusion created a
complemental doping.

Then you have the hard part of the job in the delivered kit.

The wafers were allowed to cool and then the carbide was used to remove
the surface on one side of the wafer to get back down the original silicon. I
forget exactly how the wires were added to each side, probably a loose flat
spiral of bare copper held in contact mechanically. When finished the kids had
a working solar cell.

My brother was given the kit by his science teacher to put together on
his own for "extra credit". I suspect the teacher just wasn't up to the task of
using the kit the way it was intended. I got the kit and played around with it.

So, in short, you CAN manually dope silicon without Billions of dollars
of equipment. I know because I've done it.

The problem is with the word _manually_. Obviously anything that can be done by a machine can be
done by hand. Obviously with enough hardware for doing it and testing it and enough experimentation
one can learn to get the results desired. However anyone who has looked into the process would know
the right answer and not ask the question.

The question appears in line with the kit you mention. Is there a simple way to do it? is more like
the question sounds and the answer is no. And with the kit efficiency was likely so low that a high
impedance voltmeter was needed and no way to measure the current short of lab equipment the
efficiency would be so low compared to even the cheapest commercial production.

So the answer is also no if the intention is a "try and see" bright idea. The idea might be sound
but the success so low as to be unmeasurable. So again the answer is no. And again anyone who knew
the difficulties involved would not ask the question.

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