Electron Hole Pair: How Does Charge Conservation Apply?

[phrygian]

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

 

[abhi2005singh]

...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?

 

[Cthugha]

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.