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Electronics book teaching from electron theory flow

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Ash Small

Thu May 12 2011, 11:01AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Steve McConner wrote ...

I have heard of a basic electronics course that took semiconductor physics back to regular wires, and referred to conventional current as "holes", but I thought this was a really stupid idea.

This also puzzled me when I was younger. Still does a bit.

At school I learned about anions and cations. Electrons are cations (emmited from the cathode, travel to anode). Is there any fundamental difference between 'holes' and anions (emmited from anode, travel to cathode)?

Is 'the movement of holes' the same as 'the movement of anions', or is there a difference?

This has always puzzled me. (I think I've used the correct terminology here)

Why are things not simply referred to as 'anode', 'cathode', 'anion' and 'cation'?

Steve Conner

Thu May 12 2011, 11:19AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Anions and cations are terms from chemistry.

But if you want to get all interdisciplinary, I guess electrons are cations and holes are anions. There is a fundamental difference because the electrons and holes in semiconductors are constrained by a crystal lattice with special quantum behaviour, but the anions and cations in a solution are influenced by the molecules of the solvent in a different way.

In particular, an anion is an object, but a hole is an "absence of object"- an empty bubble in a sea of valence electrons. So, when an electron and a hole meet in a semiconductor they annihilate, but when an anion and a cation meet they do something chemical.

The physics are similar enough that you can make electrolytic diodes

and so on. An electrolytic transistor would really be something.

Ash Small

Thu May 12 2011, 12:41PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

This is what has always puzzled me. I've read that the difference between NPN and PNP is that one involves the movement of electrons accross a junction, and the other involves the movement of holes accross a junction, but you're saying the holes don't move (which I can follow and which makes sense, crystal lattice and all that)

I can follow that the movement of electrons in a conductor can be compared with the movement of cations in an electrolyte, but the explanation of 'hole migration' in a lattice just baffles me. Isn't it just a case of electrons moving in the opposite direction?

BTW, I believe it forms part of the 'interface' between physics and chemistry that is referred to as 'physical chemistry'.

(I'll read up on electrolytic diodes later, thanks for the link)

Pinky's Brain

Thu May 12 2011, 02:32PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837

Steve McConner wrote ...

But as was pointed out, semiconductors can have charge carriers of either polarity or even both polarities at once

It's a useful abstraction, of course with few exceptions (materials with ionic currents, not semiconductors) the electrons are still the only thing really moving.

Mattski

Thu May 12 2011, 05:00PM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

wrote ...
I can follow that the movement of electrons in a conductor can be compared with the movement of cations in an electrolyte, but the explanation of 'hole migration' in a lattice just baffles me. Isn't it just a case of electrons moving in the opposite direction?

That's precisely correct. Consider a water bottle with some air at the top. Invert the bottle and the bubble goes to the bottom and floats back to the top. But equally you could view the water as flowing downward to fill the void that is the bubble. But it's easier to think of the bubble floating up than water flowing in to fill the void.

Similarly the hole is much easier to keep track of because in the valence band almost ever electron state is filled, so there is a huge sea of electrons with just a few holes in it. Since a hole moving left is the same as an electron moving right from the purposes of charge transport we keep track of holes movement instead of electron in the valence band.

In the conduction band you keep track of electron movement because in that band most available electron states are unfilled (holes), and there is just a small number of electrons present. So in this case it's easier to track the electrons directly.

radiotech

Sat May 14 2011, 05:53AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

Steve McConner wrote "The physics are similar enough that you can make electrolytic diodes and so on. An electrolytic transistor would really be something"

The came and went long ago, they were called "Solions"

I think US Navy developed them at Philadelphia. There were
electrolytic diodes and tetrodes etc. They were so incredibly slow
they were used in integrator circuits. SE110 is a solion tetrode.

Steve Conner

Sat May 14 2011, 08:53PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Thanks for the tidbit of info, radiotech! I was worried the other day that I was talking pure nonsense about electrolytic transistors, so it's nice to see that they existed.

A solion looks like something that could easily be made by a hobbyist, if you could find the recipe. Amateur device making seems to be cool nowadays: Nyle Steiner, the guy whose borax rectifier I showed, also made a FET out of one of those cadmium disulfide photocells.

radiotech

Sun May 15 2011, 03:22AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

This is as close to a description I have ~~55 years ago. Later books here just seem to copy parts of it.

radiotech

Sun May 15 2011, 03:28AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Posts: 1546

Here is something. hugh old book..

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