Back in February, I visited one of the small museums that exist in the town where I
live. It's a natural history museum and is based in an old church. It's a lovely
place to visit, with lots of curious things to look at. In the shop, on the way out,
there was a basket with small chunks of rocks and minerals for sale and I bought a
small piece of 'fool's gold' (iron pyrites); I figured that an old fool like me
deserved a piece of gold to treasure.
What I didn't know back then and have only just discovered is that iron pyrites is
a semiconductor (thank you, Wikipedia!) and in the old days was sometimes used as
the 'crystal' in a point-contact diode (for demodulating radio signals in a crystal
set).
Well, I thought, that deserves an experiment. So here is my attempt to make a
point-contact diode, and it turned out to be surprisingly easy. I simply broke one
of the small cubes away and held it in one clip of a 'helping hand' contraption.
That clip I connected to the ground of a signal generator. The drive from the
generator I fed through a 10k resistor to a piece of wire-wrap wire which I arranged
to scrape across the surface of the cube. My scope then measured the output from my
improvised diode.
A little movement of the wire and I soon found a spot that rectified nicely [I was just
so surprised - I really didn't think that this was going to work].
The forward voltage looks to be a little over a volt. That's much higher than a
silicon metal-junction diode (a Schottky diode).
And that's it. No need to melt silica in an oven and grow it into a crystal with
99.99-whatever % purity. Instead, an instant semiconductor straight from nature.
Do I get a cat badge for this foolishness?
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