What happens when p and n type semiconductors meet?

[Bassalisk]

When p and n meet they form a junction. Shortly after a depletion zone is formed.

I have a question about this forming. Probably the obvious answer.

Near the junction, electrons from n-type crossover into p-type and fill those electron holes, leaving their mother atoms(5 valence ones) immobile positive ions, and when acceptors accept those electrons, they become negative ions. Atoms near that depletion zone are immobile, and this recombining of the electrons and holes makes those atoms ionized and this creates that electric field? And because there are no charge carriers there, this is called depletion zone?

Am I thinking right here?

 

[dlgoff]

Sounds okay to me.

Filling a hole makes a negative ion and leaves behind a positive ion on the n-side. A space charge builds up, creating a depletion region which inhibits any further electron transfer unless it is helped by putting a forward bias on the junction.

For more details, see http://hyperphysics.phy-astr.gsu.edu/hbase/solids/pnjun.html"

 

[Nikarus]

Hi all,
I'm trying to understand P-N junctions as well.
I read a lot of explanations, but still there is one thing bothering me. Probably I should ask it in another topic, but still...
Can you please explain me this part:

when acceptors accept those electrons, they become negative ions

I don't understand - acceptors are atoms with electron lack (hole) correct? So it means that acceptor is positively charged. So when acceptor accepts an electron, it should become neutral, not negative.
Can you please point out what I'm missing?

 

[uart]

Hi all,
I'm trying to understand P-N junctions as well.
I read a lot of explanations, but still there is one thing bothering me. Probably I should ask it in another topic, but still...
Can you please explain me this part:

I don't understand - acceptors are atoms with electron lack (hole) correct? So it means that acceptor is positively charged. So when acceptor accepts an electron, it should become neutral, not negative.
Can you please point out what I'm missing?

Both explanations (yours and the OP's) are somewhat incorrect.

The acceptor atom grabs a valence band electron from the normal Si lattice as soon as the p-type semiconductor is formed. So the acceptor ion is negative from the get go. Overall charge neutrality is maintained by the fact there is now a positively charged Si atom that is short of a valance electron (that is, what we call a hole) somewhere nearby.

The reason that a Hole is mobile, despite the fact that valance electrons are normally NOT mobile, is because although they (v-band electrons) don't have enough energy to get up and wander about the lattice like their conduction band counterparts do, they can however tunnel from an adjacent atom into the hole if one is close enough.

When an electron diffuses across from the N side of the junction it combines with a hole and so upsets the local charge neutrality that was previously maintained between the negative acceptor ion and the positive hole.

 

[Nikarus]

Hi uart,
Thank you very much for your explanation!
So, this means that molecule of p-type semiconductor is neutral but it has this mobile "positive charged" hole. And because of this, it can take a new electron and become negative ion.

I think I got it now. Thank you!

 

[uart]

So, this means that molecule of p-type semiconductor is neutral but it has this mobile "positive charged" hole.

Yes, most of the Si atoms in the P material are neutral but a (relative) few have a net positive charge. These holes exactly balance the charge of the acceptor ions, all of which are negative.

And because of this, it can take a new electron and become negative ion.

The Si atoms with the positive charge (the holes) can take a new electron and become neutral, upsetting the local charge balance that was previously maintained between the +ive holes and the -ive acceptor ions.