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  Electrons and Holes 
 Date Written 
silent snow Feb 15, 2003, 10:00pm EST Report Abuse
First of all I would like to thank you for writing this fine article. I am a Sophomore Chemistry student in the New York suburban area, and this article is very easy to follow and yet very informative.

I stumbled across a small misunderstanding on my side:

Quote: "it is not difficult to see that electrons can move much more easily than holes"

As far as I understand, holes can only move through the process of electron movement. Thus, holes cannot move without electron movement. Therefore, should you not have said that holes cannot move by themself?

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silent snow Feb 15, 2003, 10:06pm EST Report Abuse
>> Re: Electrons and Holes
Minor comment:

Quote: "...The result is the creation of an Electron-Hole Pair. Both the newly created electron and hole are available to aid in conduction of current through the material..."

I think you should insert the word "free" between "created" and "electron" as you are not creating an electron. Instead, you are creating a free electron from a trapped electron.

Dan Mepham Feb 15, 2003, 10:29pm EST Report Abuse
>> Re: Electrons and Holes
Re your second comment, I agree. I've inserted the word 'free' as you suggested. It should be there to make the clear distinction that we're talking about 'creating' a *free* electron for conduction, not magically creating a new electron period.

Re your first comment; yes and no. Holes are an abstraction. There's no such thing as a hole .. rather a hole is an empty bonding space in the valence band into which electrons can fall. In that respect, you're absolutely right - a hole does not move. A hole is nothing. The only way we conceptually perceive holes moving is through the movement of electrons.

However - and here's the distinction - a hole can move by itself, in so far as it does not require a *free* electron to do so (there's that distinction again). Hole movement requires electrons *period*, but they do not have to be free electrons (i.e. electrons in the conduction band).

It somewhat makes sense if you think about it. You do need electrons *period* for hole conduction. If you had no electrons whatsoever, we'd simply have a material jam-packed with holes, which means they couldn't move anyway! So hole movement, then, requires no free electrons in the CB, but rather consists of the shuffling around of all the electrons in the VB. From there, it again makes sense to say that it would be easier for a single electron to travel through a conduction band, than for a whole pile of electrons to have to shuffle around in the valence band to constitute hole movement.

Does that answer your question?

Dan Mepham
Dan Mepham Feb 15, 2003, 10:37pm EST Report Abuse
>> Re: Electrons and Holes
Perhaps I could add another comment to clarify further.

This quote.. "it is not difficult to see that electrons can move much more easily than holes" is referring to the movement of FREE electrons, versus the movement of holes. That is, it is saying that, of the two types of charge carriers, free electrons in the conduction band, and holes in the valence band, the free electrons move more easily.

It is not saying that *all* electrons move more easily than holes. It is saying that the free electrons in the CB move more easily as charge carriers than their hole counterparts in the VB. One electron moving in the CB is just that; one electron moving. One hole moving in the VB, on the other hand, is actually thousands if not millions of electrons shuffling around.

Hopefully that makes some more sense. :-) I'll re-read over that quoted sentence to see if it can be made more clear.

Dan Mepham
silent snow Feb 26, 2003, 12:58pm EST Report Abuse
>> Re: Electrons and Holes
Thank you, I understand now.



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