Electrons and Holes (ARRL)

This is from the ARRL handbook 2010 p5.12:

"When energy is added to a semiconductor lattice, generally in the form of heat, some electrons are liberated from their bonds and move freely throughout the structure. The bond that loses an electron is then unbalanced and the space that the electron came from is referred to as a hole.

Electrons from adjacent bonds can leave their positions and fill the holes,thus creating new holes in the adjacent bonds. Two opposite movements can be said to occur: negatively charged electrons move from bond to bond in one direction and positively charged holes moves from bond to bond in the opposite direction. Both of these movements represent forms of electrical current."

I personally think this is wrong. The electrons moving from bond to bond and the holes are the same thing. The two currents should be :

1- The hole/bond electron current moving from bond to bond (closer to the lattice structure)
2- The free electron current caused by high energy electrons that are no longer associated with any bond.

I'm saying this because my understanding is that holes are not real. A holeis an absence of an electron, and hole movement is really bond electrons moving.

 

What Phil said....
I just wanted to add that you can use the Hall effect to determine
the sign of the charge carriers in a conductor. If you look at n-
doped Silicon (extra electrons.) you'll find a negative sign. And
with p-doped a positive sign. That makes holes look 'real' from my
perspective.

George H.

 

Take a row of marbles in front of you. Remove one in the middle.
Take the marble right of the empty space and put it in the empty space.
repeat that a number of times.

You see that the hole moves to the right.

 

Thanks for the responses. But it appears to me that what what everyone said is more in agreement with what I said, maybe expressed better.

This is more or less what I tried to express when I said:

So in essence #1 in my description is what you described as valence electrons, while #2 is conduction band electrons.

However the excerpt from the ARRL handbook makes it look like (at least to me) that the two currents appear in the valence band, and that in valence band, hole and electron currents are two separate and distinct currents, which I thought is wrong.

 

Thanks!

On another note, I have a copy of Grey and Meyer. I'll use it as my semiconductor physics reference since my budget for "way over my head" books has run out. I'll certainly add Sze's book to my wishlist.

 

"tuinkabouter" wrote in message

Whereas for electron movement you could add an extra marble in one position,
and then move it to adjacent positions. You can move it faster, too, since
you can just keep moving the same marble. For hole movement, you must move
many different marbles.

That seems to be a good way to visualize it, and possibly also to understand
the difference in mobility.

Paul

 

You got me.

(Making shelf space)

 

As an undergrad we used a book by Ben Streetman. ("solid state
electronic devices")
I've got the second edition of that which is a bit like Sze but at a
lower level.
I notice it's up to it's 6th edition and you can get earlier ones of ~
$4.00 ($0.01 plus s&h.)

Sze is nice but it is a bit of a tome. (No one but Phil H. is going
to read it like a novel... :^)

George H.

 

Ben Streetman was my undergrad advisor. Good guy but was none too
happy when I first dropped the (required) course. The prof wasn't
teaching and I wasn't getting. I took it again the next semester, with
him teaching, and had no problems.

 

Grin... I was mostly just poking fun at you.

I do agree with your approach to a new field.
Which for me is to get a good *undergrad* text on the subject and read
through it... ignoring the math (mostly). Then go back and re-read
what you are interested in. My only (minor) observation is that Sze
is not an undergrad text... and I was suggesting something pitched a
bit lower.

George H.

 

I always tell undergrads to pick their courses, not by the subject
matter, but by who is teaching them. This means taking courses out of
'sequence' sometimes, but I never found that to be much of a problem.
(And sometimes there is no good teacher and you have to learn it on
your own...)

I have no memory of the class wherein I used Streetman's book. I
rediscovered it on my shelf in grad school.

George H.

 

Well sure one should always start with the exteneded zone scheme
before doing the folded zone thingie. I'm not sure Streetman does
any of that. (I'm pretty sure he's an EE.) I saw this nice talk at
the last APS meeting about optical lattices, and they use all the
solid state 'language' of Bloch states. It's pretty cool, cause they
can change the lattice parameters with just a tweak of the laser.

Gotta leave something for grad school :^)

Ouch! Organic chem was my only C, I never got it and I'm not smart
enough to memorize it all.

I've always wanted to go back and do it over. There must be some
underlying principles that I just missed. (Maybe too much beer
drinking during the first weeks of the semester?)

George H.

 

Hmm I think you were supposed to 'cook' the book in a H2SO4 3 molar
solution at 60C for 30 minutes before throwing it in the
Charles. :^)

George H.

 

I've still got my organic chem tome on the shelf, I reread the first
few chapters several years ago... It seemed to make sense... after
that it's a zoo of different 'elements'.
"Intro to Organic Chem." '76
Streitwieser and Heathcock.
(just dug it out)

There's a list of NMR chemical shifts behind the front cover.
(I would have had no idea what those were when I took the course :^)


George H.