On Sat, 04 Jun 2005 18:47:44 GMT, 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.

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.

Jim

Thanks, Jim, for that post. I had started to respond similarly here,
with my own twists and then read what you wrote -- with more detail
than I remembered, actually.

I think the kit that Bell Labs put out was back in the early-to-mid
1960's. I recently spoke with the people who currently own the rights
to this kit (recently being a few years ago) and they are/were still
selling it. Unfortunately, it would be very difficult for me to find
the phone number, today -- it was in 2001 when I last had this
information at hand. But they were on the east coast.

to the OP:

Modern, pure silicon wafers are rather cheap, thanks to the number of
them being processed. I haven't directly purchased any, but someone
at HP's Deer Creek facility told me they were only a "few dollars
each" (my memory says the figure was near $4) when I pointed to the
boxes and boxes of them they had laying around. This is sliced,
polished, and cleaned so that no particles larger than a micron
remained, if memory serves. Perhaps you could contact a fab or
someone who might know someone at one who might help you get fragments
of broken ones. I use such broken pieces (which I treat rather
poorly) as convenient and well studied reflectors/filters, sometimes.

However you proceed, if it is based on choices you are making and not
on someone else's well-thought-out design, you should research it
well. If you are considering doing this "manually," then you should
study how these things were done when there were no fabs and they were
just experiments in laboratories. And run anything you come up with
by a knowledgeable chemist before you try it. You will want an
informed opinion about the risks and mitigations and advise about what
to consider trying. Hot materials can easily produce noxious gases.

As a side bar, I've built ovens from spare parts that could easily
raise a wafer to passivating temperatures, such as near 1500 C for
rapid oxide growth, that sat in my garage. Just for testing some
optical ideas, not for making wafers, though. Got plenty of free
wafers from fabs, no problem. Used 'plenty' of dry nitrogen gas to
fill the chamber (1500 C and open air with 20% oxy isn't so good an
idea) and keep it at slightly higher pressure than ambient so oxygen
doesn't get inside. Cripes, do things become a mess if you forget to
run the nitrogen! You can construct quite a nice little "oven" of
your own with a water cooled quartz jacket and some tungsten lamps
from your local hardware or home construction store, a power
controller, and a nickel plated chamber (much, much cheaper than gold
and works "pretty good".) Just a tap water flow is usually enough.
You don't want the quartz to get too hot, as it grows more opaque
where it counts when it does and absorbs even more energy and melts in
the resulting positive feedback. With a few kW of lamp energy and not
enough cooling, bad things happen.

In any case, don't plan on building much other than a solar cell to
start. And keep things really simple and as safe as you can, as you
learn.

Jon