Electron Hole Pair: How Does Charge Conservation Apply?

In summary, when an electron in a semiconductor is excited, it creates an electron hole pair. This does not violate charge conservation because the hole is simply the absence of an electron and is always present in the semiconductor. The promotion of an electron to a higher state also moves the absence of that electron, maintaining a net charge of 0.
  • #1
phrygian
80
0
When an electron in a semiconductor is excited to a higher state, an electron hole pair is created. How does this not violate charge conservation, a charge of +e turns into a net charge of 0?

Thanks for the help
 
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  • #2
...a charge of +e turns into a net charge of 0?

It is not clear as to what you mean by this. Where is +e charge which is converted to 0 charge?
 
  • #3
You do not seem to fully understand the concept of electrons and holes.

Before an excitation process happens, you have something similar to a valence band full of electrons and a conduction band without electrons (or equivalently full of holes). During excitation one electron is promoted to the conduction band and one hole goes to the valence band. If you imagine the hole as the absence of an electron (simplifying picture, but ok for the beginning) it is easy to understand that any promotion of an electron from some band to another band will automatically also move the absence of that electron from the second to the first band. There are no charges created. The hole is always there.
 

1. What is an electron-hole pair?

An electron-hole pair is a phenomenon that occurs when an electron in a solid material is excited to a higher energy level, leaving behind a positively charged space known as a hole.

2. How is an electron-hole pair created?

An electron-hole pair is created when a photon or another form of energy interacts with a material, causing an electron to jump from its original energy level to a higher one, leaving behind a hole with a positive charge.

3. How does charge conservation apply to an electron-hole pair?

Charge conservation states that the total electric charge in a closed system must remain constant. In the case of an electron-hole pair, the positive charge of the hole balances out the negative charge of the excited electron, ensuring that the overall charge of the system remains the same.

4. What is the significance of an electron-hole pair in semiconductors?

In semiconductors, the movement of electron-hole pairs plays a crucial role in the flow of electric current. This allows for the creation of electronic devices such as transistors and diodes.

5. Can an electron-hole pair be separated?

Yes, an electron-hole pair can be separated by an external electric field, causing the electron and hole to move in opposite directions. This process is known as charge carrier recombination and is essential in the functioning of solar cells and other optoelectronic devices.

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