So i've been a bit confused, looking at PN junction, semiconductors and the like (trying to nail down how exactly semiconductors work, transistors and such). I've read the wiki on band structure (“holes” and free electrons).
Apparently the big part is the band theory, and how the energy levels work. This is what I have so far (correct me if I’m wrong):
Materials/atoms have energy levels and bands based on these energy levels.
The forbidden band (I’m assuming closest to the atom): no free electrons are allowed in or out.
Above that is the valence band, which can force free electrons out with some energy leaving behind a “hole”. The valence band is usually pretty well occupied (Does this mean it might have some “unoccupied holes” in it?).
Electrons in the conduction band, I’m assuming, take very little energy to move out of the atom (or are already leaving the atom).
The band gap determines how much energy it takes to remove an electron from the valence band to the conduction band (Insulators have a big gap, semiconductors’ gap is small. But does it, maybe, grow larger with heat?).
So, I have a few questions:
When an electron leaves a valence band, does it leave behind an actual hole, or is that just conceptual? What determines how “filled” a band is? How come electrons cannot just slide on into a band?
When an electron reaches the conduction band, is it “free” from the atom? Or just takes very little energy to get discharged?
When we refer to charge carriers, what is this? A Femi Gas? Are there holes in this gas that can move? Or do just electrons move in and out through the gas? I’m guessing the concept of “holes” has me slightly confused as I don’t understand how a hole can “move”.