Home-made diode/transistor

A project log for today's assorted project ramble "grab-bag"

Assorted project-ideas/brainstorms/achievements, etc. Likely to contain thoughts that'd be better-organized into other project-pages

esot.ericesot.eric 08/26/2019 at 04:314 Comments

It really seems to me there must be ways to make transistors with household supplies/tools... yahknow, without a microscope or nasty chemicals or special oven or, most importantly, pre-fab semiconductor-materials like silicon wafers. Here's where my research led...

metal rectifier is an early type of semiconductor rectifier in which the semiconductor is copper oxide...They were used in power applications to convert alternating current to direct current in devices such as radios and battery chargers.
Metal rectifiers consist of washer-like discs of different metals, ...copper (with an oxidelayer to provide the rectification) ... interspersed with aluminium discs (which were often of a larger size, to provide cooling).
The principle of operation of a metal rectifier is related to modern semiconductor rectifiers (Schottky diodes and p–n diodes), but somewhat more complex. copper oxide [is a] semiconductor, in practice doped by impurities during manufacture

[Hey, i've got some of these!]

Copper(II) oxide is a p-typesemiconductor, with a narrow band gap of 1.2 eV.
It can be formed by heating copper in air at around 300 – 800°C:
2 Cu + O2 → 2 CuO

"In the history of semiconductor physics, Cu2O is one of the most studied materials, and many experimental semiconductor applications have been demonstrated first in this material:

[A bit of confusion regarding *which* copper oxide, carries forth later-on as well]


Shockley's research team initially attempted to build a working FET, by trying to modulate the conductivity of a semiconductor, but they were unsuccessful, mainly due to problems with the surface states, the dangling bond, and the germanium and copper compound materials. In the course of trying to understand the mysterious reasons behind their failure to build a working FET, this led them to instead invent the bipolar point-contact and junction transistors.

Hah! So mosfets were the goal in the first-place! Then failing that, the bjt was born as essentially a mistake... then twentyish years later the technology existed for the *original* goal.

The problem with the realization of a working metal-insulator-semiconductor (MIS) field-effect transistor (FET) is the interface between the semiconductor and the insulating dielectric. This was obviously also the case with the experiments on the semiconductor cuprous oxide (Cu2OCu2O), which was historically used as a rectifier. John Bardeen (double Nobel prize winner in Physics) found that this problem is caused by interface states at the insulator/semiconductor interface which hinder the penetration of the electric field into the semiconductor thus preventing the modulation of a mobile charge layer (conducting channel) near the surface necessary for the field effect transistor. In the course of the experimental investigation of this problem with conducting probes on the semiconductor surface (germanium), Bardeen together with Brattain serenpitously discovered the bipolar transistor effect which led to the realization of the point contact bipolar transistor and later the junction bipolar transistor. Very few insulator/semiconductor interfaces have low enough interface state densities to be suited for a field effect transistor. Only in 1960 the first operating MISFET was demonstrated by John Atalla and Dawson Kahng. This FET, a metal-oxide-semicondoctor field effect transistor (MOSFET), used a specially prepared  film on silicon () to obtain an interface with very low interface state density.


[Which actually differs from BJTs]


But here we go. Dude's tried it.

Shoulda known...

Visit his site, look around for parts 2 and 3, in which he develops electrolytic diodes with baking powder, aluminum foil, copper, and water, and uses them to decode a 7-seg display!

Then search for "electrolytic transistor" and prepare to brainstorm.

Also, check this out, creating audio from electrochemical reactions:


Ken Yap wrote 08/26/2019 at 09:33 point

I just steal some whiskers from my cat.

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esot.eric wrote 08/26/2019 at 09:36 point

har har har

Got plenty of germanium laying around, do ya?

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Ken Yap wrote 08/26/2019 at 09:55 point

I did actually find some OC71 and similar transistors in my box. But not a lot, probably micrograms in there. Cat whiskers were actually typically used on galena (lead sulphide).

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esot.eric wrote 08/26/2019 at 18:35 point

I did read that point-contact diodes could be hacked into transistors. Pretty wild. 

The Copper-oxide diode-experimenter used a point-contact, but I think for different reasons. The way he created the oxide-layer was to heat the copper with a candle... a barely-controlled process which left the surface somewhat randomly-coated with various oxides and I'm sure other things. So his point-contact, if I understand correctly, was used to probe around the surface [with attached oscilloscope] until the right spot was found.

I don't think the copper-oxide rectifiers of old required a point-contact... they probably controlled the oxide layer to a great extent. And the large interface allowed for large currents.

But, I haven't quite wrapped my head around the other point-contact devices, I gather that the small contact-area has something to do with the electron/hole density necessary. And the two-point transistor, especially...

I also gather that the point-material, though allegedly gold on the first transistor, is not particularly chemically/electrically important, more that it needs to be thin, and maleable-enough to make good contact without slicing through the oxide... e.g. a "whisker" made of unmelted solder pulled right off a spool [maybe formed a bit into a small diameter, or squished into more of a sheet] would probably do.

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