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Valence and conduction bands in an n-type material

by paulmdrdo
Tags: bands, conduction, material, ntype, valence
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paulmdrdo
#1
Jan16-14, 10:52 PM
P: 4
can you explain why the trivalent impurities
exert lower forces on the outer-shell electrons than the pentavalent impurities?
and why The valence and conduction bands in an n-type material are at slightly lower energy levels
than the valence and conduction bands in a p-type material?
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Simon Bridge
#2
Jan16-14, 11:17 PM
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Welcome to PF;
Where is that coming from?

As usual the devil is in the details:
For silicon - donors come from group V and acceptors from group III ... have a look at those atoms on the periodic table. Match up the general properties of these groups with their performance as semicondctor impurities.

Simplistically: trivalent impurities kept all their electrons while the pentavalent impurities lost one ... electrons are going to be more attracted to the location an atom lost an electron than to one where the atom has not right?
paulmdrdo
#3
Jan16-14, 11:27 PM
P: 4
I've read it from electronics book.

Now, if the trivalent impurities kept all their electrons, does it mean the electrons are experiencing higher attractive force of the nucleus? hence have lower energy? I'm still confused. what i'm most concern about is the difference of energy levels of the conduction and valance band of p-region and n-region.

Simon Bridge
#4
Jan16-14, 11:32 PM
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Valence and conduction bands in an n-type material

Maybe I misread the question ... how do you mean "outer shell"?
I still need to know where you are getting this, I'm only guessing.
paulmdrdo
#5
Jan16-14, 11:38 PM
P: 4
here's the complete paragraph

ENERGY DIAGRAMS OF PN JUCTION AND DEPLETION REGION.

The valence and conduction bands in an n-type material are at slightly lower energy levels
than the valence and conduction band s in a p-type material. Recall that p-type material ha s
trivalent impuritie s and n-type material has pentavalent impuriti s. The trivalent impurities
exert lower forces on the outer-shell electrons than the pentavalent impurities. The lower
forces in p-type material s mean that the electron orbits are slightly larger and hence have
greater energy than the ele ctron orbit s in the n-type materials.

I don't understand the part where it say that "the trivalent impurities exert lower forces on outer-shell electrons(valence electrons) than the pentavalent purities. The lower
forces in p-type material s mean that the electron orbits are slightly larger and hence have
greater energy than the ele ctron orbit s in the n-type materials."
Simon Bridge
#6
Jan17-14, 12:07 AM
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Hmmm... not a very clear description is it.
They appear to have mixed atomic and band-structure descriptions.

I think: list the elements in each group - and look up their energy levels.
Compare.


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