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Just wondering if it is possible/viable to construct your own transistor, not small like todays, but the same scale as the one created at Bell Labs.

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up vote 6 down vote accepted

You might find the Yahoo "home_transistor" group a useful resource.

There's also a series of videos on YouTube by Jeri Ellsworth including some where she makes transistors. In one, in particular, she takes the crystal out of a germanium point-contact diode and turns the crystal into a point-contact transistor (much like the Bell Labs transistor.)

There are a couple of semiconductor materials that are easy (and relatively safe) to make at home. One is cuprous oxide. H.P. Friedrichs has a page where he shows how to make a copper/cuprous oxide diode. (The copper/cuprous oxide junction is a schottky barrier). There's also a page at the science cupboard where they make cuprous oxide diodes.

Another easy home semiconductor is titanium dioxide. Here is a page at University of Wisconsin talking about how to make titanium dioxide solar diodes.

Transistors are hard to make because they require two rectifying junctions, one of which, the emitter, needs to be injecting. (The emitter needs to send minority carriers into the base.) Thus the emitter/base junction needs to be either P+/N or N+/P. If you are using Schottky junctions, as the first Bell Labs transistor did, then only certain metals form injecting barriers while most do not. Additionally the base on a transistor needs to be narrower than the recombination distance for the material you are using. For most materials this is less than 10 microns (which is a distance you can work with at home, but only with a great deal of care.)

It might be easier to start out with a JFET or a MESFET. These will exhibit switching behavior but require only a single rectifying junction. (A P/N semiconductor junction in the case of a JFET and a metal/semiconductor Schottky junction in the case of a MESFET.)

I've been trying to make a cuprous oxide mesfet, but haven't had any luck yet. (Honestly, I've been doing more "research" than "trying", so it might not actually be that hard.)

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+1. Unfortunately, I can only give +1. :) Very nice answer. –  Mike May 23 '13 at 13:34
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I do believe that yes. The most hard part will be to obtain the materials.

If you manage to get a good piece of n-type (or p-type) Silicon, big enough to allow you to work with home tools, you'll "just" have to do local oxidation (with temperature for example) and make some soldering.

Of course, the quality of that transistor would be very doubtful as it would likely damaged in the first operation attempts...

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