# Homework Help: Can anyone tell me how the hole will move after this?

1. Jun 15, 2013

### anhnha

Here is a set of pictures showing the ways electrons and hole move under electric field.
Can anyone tell me how the hole will move after this? I mean that where the hole will move after the final image.

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2. Jun 15, 2013

### Staff: Mentor

It will get filled with an electron from the wire.
The wire is probably not a semiconductor, it does not have a gap between valence and conductance band and you have a lot of electrons (filled energy states) and a lot of empty energy states to conduct current.

3. Jun 15, 2013

### anhnha

Thanks mfb,
But then the hole will disappear and valence band doesn't have any hole left?
It can't conduct in valence anymore?

4. Jun 15, 2013

### Staff: Mentor

Unless you get new excitations: right.
Well, usually you have many electron/hole pairs in the material at the same time, and some new pairs are created all the time. This leads to the (bad) conductivity of pure semiconductors.

5. Jun 15, 2013

### anhnha

Hi, I don't understand that. Can you tell me what do you mean "excitation". Can I consider battery as an excitation? And how pairs of electron and hole are create?

6. Jun 15, 2013

### Staff: Mentor

Excitation is the process that lead to picture 1: thermal energy, light or whatever kicked an electron out of the valence band into the conduction band.

7. Jun 15, 2013

### anhnha

Hi,
For example, I have a P material and I apply it with a battery like the figure above.
Assume that there is no thermal energy, light or whatever kicked an electron out of the valence band into the conduction band. Then the current only flow in the circuit for a short time. Then it ceases.
Is this right?
I always think that when negative pole of battery put an electron into the hole ( in the final image above) then at the same time positive pole has to pull an valence electron into wire to positive pole and a new hole is created on the left.
Is this wrong?

8. Jun 15, 2013

### Staff: Mentor

With doping, the material will continue to conduct - at the positive side, holes are created all the time, they flow to the negative side and get filled.

9. Jun 15, 2013

### anhnha

Do you mean that holes are created at the positive side by electric field from the battery pulling valence electrons and leaving holes?

10. Jun 15, 2013

### Staff: Mentor

Right.

11. May 7, 2014

### anhnha

I would like to ask some more questions.
In pure semiconductor, thermal energy will create electron-hole pairs all the time. If there is not recombination ( I mean electrons go from conduction band to valance band) then the current will continue forever and the pure semiconductor will become a good conductor.

For example, at t=t0, thermal energy creates 1000 electron-hole pairs. From that time there is no recombination at all. This means that the pure semiconductor will always have 1000 holes or more.
Therefore, the semiconductor will act as a p type? Is that right?

12. May 8, 2014

### Staff: Mentor

Of course there is recombination. The small number of electrons and holes is "always"* in an equilibrium between recombination and thermal excitation.

*in all relevant cases