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 through out the structure. The bond that loses an electron is then unbalanced and t he 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 on e direction and positively charged holes moves from bond to bond in the opp osite direction. Both of these movements represent forms of electrical curr ent."

I personally think this is wrong. The electrons moving from bond to bond an d 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 l attice structure) 2- The free electron current caused by high energy electrons that are no lo nger associated with any bond.

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

Reply to
M. Hamed
Loading thread data ...

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.

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."

the holes are the same thing. The two currents should be :

lattice structure)

longer associated with any bond.

an absence of an electron, and hole movement is really bond electrons moving.

A hole is real if a clearing in the forest is real. Calling it a hole makes it easier to visualize and calculate with, just as it's easy to measure the area of a clearing, say.

The distinction is really that when holes move, it's valence-band electrons that are changing state, whereas the mobile electrons are in the conduction band. The two bands' energy vs momentum diagrams have different curvatures, which gives electrons and holes different effective masses and hence different mobilities.

In any case, trying to re-invent a theory that you don't understand thoroughly is likely to lead to a lot of wasted time. The math isn't particularly difficult, so if you have the background and the interest, I suggest getting a copy of the second edition of Sze's semiconductor physics book, read it like a novel, and then go back to the parts that weren't clear. (There's a third edition of Sze, but it was revised by somebody else and it isn't anywhere near as good as the second edition. Besides, the second edition is cheaper.)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
 Click to see the full signature
Reply to
Phil Hobbs

f heat, some electrons are liberated from their bonds and move freely throu ghout 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.

s, thus creating new holes in the adjacent bonds. Two opposite movements ca n 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 o pposite direction. Both of these movements represent forms of electrical cu rrent."

and the holes are the same thing. The two currents should be :

lattice structure)

longer associated with any bond.

le is 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.

Reply to
George Herold

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.

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."

the holes are the same thing. The two currents should be :

lattice structure)

longer associated with any bond.

an absence of an electron, and hole movement is really bond electrons moving.

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.

Reply to
tuinkabouter

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

lattice structure)

longer associated with any bond.

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.

Reply to
M. Hamed

more in agreement with what I said, maybe expressed better.

lattice structure)

longer associated with any bond.

while #2 is conduction band electrons.

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.

I see. Yes, the Handbook is wrong to talk about "bonds" here, because the action is happening among delocalized states. Inner shell electrons are bound to individual nuclei, but valence and conduction band electrons aren't.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
 Click to see the full signature
Reply to
Phil Hobbs

is more in agreement with what I said, maybe expressed better.

lattice structure)

longer associated with any bond.

electrons, while #2 is conduction band electrons.

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.

Reply to
M. Hamed

Got 8 bucks?

formatting link

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
 Click to see the full signature
Reply to
Phil Hobbs

space.

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

Reply to
P E Schoen

You got me.

(Making shelf space)

Reply to
M. Hamed

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.

Reply to
George Herold

Nah, I didn't say he had to follow all the math in his head, any more than I would. You just get the overview of where the book is going, and then go back and dig into the non-obvious parts. It's about the fastest way to come up to speed in a new field that I know of.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
 Click to see the full signature
Reply to
Phil Hobbs

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.

Reply to
krw

d
t

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.

t -

Reply to
George Herold

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.

Reply to
George Herold

Maybe that would be better. I found undergraduate solid state books really unsatisfactory, though, because they try to avoid having you know about Bloch waves, chemical potential, and aliasing. All that mumbo jumbo about k vectors crossing one edge of the Brillouin zone and magically reappearing at the other edge...when actually all that's happening is aliasing.

Of course the way stat mech is usually taught isn't too helpful either--calling an open thermodynamic system a "grand canonical ensemble" is about as stuffy as stuffy gets. (But then I'm just being bad-tempered.)

The undergrad semiconductor physics I've seen are also typically very unphysical when it comes to things like photoconductors, where the carrier lifetime can be much longer than the transit time, but the carriers don't disappear when they get to the contacts.

Basically I get impatient with technical topics that are just presented as something to memorize rather than to understand. It gives me nightmares about organic chem class. ;)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
 Click to see the full signature
Reply to
Phil Hobbs

You, too, huh? I memorized my way to an "A" in organic chem, then went out to the Harvard Bridge and threw the books into the Charles ;-) ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
 Click to see the full signature
Reply to
Jim Thompson

~
g

and

test

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.

t -

Reply to
George Herold

~

ng

, and

stest

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.

    ...Jim Thompson
      |    mens     |
    |     et      |
 |
      |

ide quoted text -

Reply to
George Herold

[snip]

I actually regret doing that. I tossed both semesters', inorganic and organic. Since then I've had occasion to need to deal with some electrochemical circuits... and had to buy some books to get back up to speed. (The Charles devoured some very good notes :-( ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
 Click to see the full signature
Reply to
Jim Thompson

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.