David Cutter wrote:
> Some semiconductors I worked with years ago were rated for 25 years
> continuous operation at maximum temperature. It was said that the
> tracks inside the part migrated to the next nearest track over time
> and stress.
I doubt the tracks themselves migrate. The semiconductor material
consists of N and P type. The narrow traces and major active parts are
doped with either donor (N) are receptor (P) type and are what are
called the majority carriers. They also have impurities for the other
types in there called minority carriers. With high temperatures the
dopant for the majority carriers tends to migrate out of the material
and contaminates that surrounding material. This changes the
characteristics of the device. Some where in there the device will fail
as adjacent material becomes contaminated.
Back in the old days devices were no where near as pure as they are
today. In the early days of the industry multi pass float zoned single
crystal which ran as much as $125USD per gram could not match the purity
of the poly crystalline silicon right out of the reactor at present.
That was in a 1/2-3/4" diameter rod single crystal rod. I'm not sure
what size they run today, but I'd say 10-14 diameter poly and single
crystal rods are not uncommon. I worked for the world's largest supplier
for many years. Since I left there and went to college full time they
have doubled the capacity of the plant at least 3 times. I believe the
last expansion ran close to 2 billion dollars and they are not only
starting another expansion, they are also "building another
manufacturing plant" down in Tennessee. They are also building a thin
film plant right next to the current poly crystal plant. Cost wise, as
a wild, semi-educated guess, I'd say they probably sell that super pure
poly which can be made directly into solar cells for less than $6 USD
per Kilo. I've had nothing to do with the industry since 87 so my
knowledge is very dated.
73
Roger (K8RI)
BTW, please ignore multiple posts. I had an e-mail reader problem and
when the system fixed it the thing regressed a couple of days.
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