Re: gEDA-user: LED in reverse

[Dan McMahill <dan@xxxxxxxxxxxx>]

Karel Kulhavy wrote:

> So the principal factor that makes the rectifying action is some kind of
> intrinsic charge that is nailed down within the volume of the material and
> encourages flow of electricity one way, and cause the flow in the other way to
> jam?

it is because (well, this is one way of looking at it) that the total 
current flow is basically determined by the minority carriers.  Thats 
electrons in the P material and holes in the N material.  When you 
reverse bias the junction, you  are trying to extract minority carriers 
and you get very little flow.  When you forward bias, you inject 
minority carriers and get a lot.  In other words, when you forward bias, 
the N side injects electrons (that it has lots of) into the P side and 
the P side injects holes to the N side.  Now you have enough minority 
carriers to have significant current flow.  Why is the current flow 
determined by the minority carriers?  It is because if you pick a single 
region, say the N-region, the total current is the current from both 
minority carriers (the holes) and the majority carriers (the electrons). 
 It is a pain to keep track of them all.  The good news is that 
undergraduate device physics is basically an accounting game.  Pick some 
thin sheet.  The carriers going in minus the carriers going out 
plus/minus any sheet of generation/recombination must give a net zero 
for a d.c. solution.  If we don't have any of those pesky sheets of 
generation/recombination (please lets keep the diode in the dark) then 
you just find the electron current on the P side and it should be equal 
to the electron current on the N side.  Do the same for the holes.  Now 
you can find electron current on the P side where they are minority 
carriers  and the hole current on the N side where they are minority 
carriers.

> Would it be possible to create the same device using an electret?

With the disclaimer that I'm not a physicist but a mere circuit 
designer, it would seem to me that you can't get a diode with an electet 
any more than you can make a diode out of a magnet.

> I read a lot of explanations how this works. I am able to learn any explanation
> like a poem, where each verse is a logical deduction I can understand. But I
> wasn't able to understand the diode at once.

It may be a lot more reading than you're looking for, but the book 
"Electronic Principles:  Physics, Models, and Circuits" by Paul E. Gray 
and Campbell L. Searle has a very good discussion of diode physics.  I 
see that you can get a used one for a pretty good price from amazon. 
Don't know what international shipping might cost.  The book was 
published in 1969 so don't view it as a handbook of modern technology. 
On the other hand, the book is quite excellent and provides a very good 
undergraduate level foundation for electonics.  It is written as a 
sophomore/junior level book intended to be covered in 2-3 semesters 
(it's just a bit over 1,000 pages).  I'd be inclined to skip the digital 
circuit stuff but the device physics is still important and the 
fundamentals of diodes and semiconductors haven't really changed.

Another decent text (well, texts) is the modular series on solid state 
devices.  You'd need volumes 1 and 2.  Volume 2 is the PN junction one 
but you need the material from volume 1 to understand it.  I'm not sure 
if this is in print still or not.

Device Electronics for Integrated Circuit by Richard S. Muller and 
Theodore I. Kamins is quite good although it is written more from the 
point of view of a device physicist rather than a circuit designer (Gray 
and Searle is more oriented I think towards a circuits person).  I have 
the 1986 version and it is good.  Haven't looked at the new one.  This 
is a senior/first year graduate level text for EE's.

If you want some online materials, check out
http://ocw.mit.edu/OcwWeb/Electrical-Engineering-and-Computer-Science/6-012Fall2003/CourseHome/index.htm
for a sophomore level course and
http://ocw.mit.edu/OcwWeb/Electrical-Engineering-and-Computer-Science/6-720JIntegrated-Microelectronic-DevicesFall2002/CourseHome/index.htm
for a senior/first year graduate course.

I can't find any online info about the text for 6.012 although I seem to 
recall hearing some complaints about the circuit descriptions in it. 
When I took the class we just had some lecture notes which were 
horrible.  Made the material much harder than need be.  I later realized 
that the class was easy but didn't appreciate that until the semester 
after I took it....  The "new" notes, which came a few years after, I 
think were quite a bit better and are what became fonstad's book.

If the book from del Alamo is ever published I'm sure it will be very 
well done.  Back when I took the class we used Muller and Kamins but 
that was before he started on his book.

This should keep you busy for a few months!

-Dan




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