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Naty1 said:Here's an interesting description:
http://en.wikipedia.org/wiki/Electron-hole_pair
While this is certainly true, it is missing something extremely fundamental that is a common practice in condensed matter physics. I'll illustrate this first using a simple metal case.
In metals, we think of there being these conduction electrons. However, are they really "true" electrons? We know that the free electron approximation is really just that, and approximation. A more detailed look at this requires us to include the many-body electron-electron interactions that occurs between all of the conduction electrons. This is where the Landau's Fermi Liquid theory comes in. This theory shows that, in the weak-coupling limit, we can make use of the mean-field approach and "renormalize" this problem from one many-body problem, into a many one-body problem. The latter is simpler, because we already know how to deal with that when we did the free-electron case (which is a many one-body problem). However, the trade-off here is that, what we have is not really a "bare" electron as in the free-electron case, but rather a "quasiparticle", which is considered as a single-particle excitation out of this many-body interaction. We lump all the many-body interactions by renormalizing the quasiparticle mass, i.e. the mass of the 'electron' you measure in a conductor can differ from the electron bare mass. It is tied to the dispersion.
So even for these electrons that people think are "real", they are really not your bare electrons, but rather electrons as quasiparticles. These are what you measure in solids.
Now, let's go back to these pesky holes. In the valence band, rather than complicate things and try to describe the dynamics of the system by describing ALL of the electrons in that band, we can simply say "Ah, let's renormalize everything and consider the holes as charge carrier". After all, we did that for the electrons already in the conduction band. So via the same method, these holes emerge as also being quasiparticles - i.e. they are endowed with mass, spin, charge, etc. They are no better nor worse than the "electron quasiparticles" that one deals with in the conduction band.
It is why, in condensed matter physics, we never argue that "electrons" are real while "holes" are not. We know better. These electrons are not "bare" electrons. They are as "real" as the holes.
Zz.