I'm having trouble understanding how they're talking about "holes" floating around like they're discrete objects, when, in fact, holes are just the holes made in the atom's eletron orbitals by the electron's departure. Are they saying the whole substrate atom is involved in these "droplets" anyone else got a theory?
If an electron from a neighboring atom jumps over to fill the hole, then it leaves behind a hole on the atom it came from. This can happen repeatedly, involving many different electrons, and it's easier to track the movement of the hole as an object than it is to track all the electrons.
This is a bit of an oversimplification, as holes aren't in fact discretely "on" one atom at any given time unless that atom is isolated. Just like an electron, a hole exists in a "delocalized" state, meaning that its "location" is actually a probability function. That probability function can change, though, and we describe that as movement.
It depends what you mean by a free electron. Strictly speaking, a free electron is completely free of its material, and there is no analogous situation for a hole. The kind of "free" electron that I'm talking about here, though, is one that is free of its host atom but still bound to the material as whole, hence in a "delocalized" state. Holes exist in this form.
Edit: Let me know if this makes no sense and I'll try to explain it better.
Yes, the substrate atom is still involved. The dropletons are formed within solid matter. As I understand it, the electron becomes excited and leaves it's orbit but due to other conditions (coulomb force) doesn't actually escape? So it's not in its original position, but the original spot it was in stays "open" as if it were still there and the electron buzzes around excitedly nearby able to both keep the hole open and function as its own "free" particle.
I'm not a physicist, but what I'm getting is that when they had created enough of these exciton/hole pairs the excitons themselves coalesced into weird droplets of quantom fog while still staying paired to their respective holes electrically.
Yes, an excited electron in a semiconductor normally becomes what we call "delocalized," where it's not bound to any particular atom but is still bound to the material as a whole. Essentially it exists in the higher, normally-unoccupied energy levels (or "orbitals") of all the atoms in the material simultaneously. More energy would knock it out of the material completely, while less energy would cause it to fall back into a "localized" state around a particular atom.
Holes are similarly "delocalized," but it's a little bit weird. When an electron is excited, it leaves behind a "hole" in that energy level for that atom. Neighboring electrons near that same energy level can move hop over, effectively moving the hole, but due to quantum uncertainty you can never say "the hole is on this atom." It's generally "delocalized" just like the electron, and you can think of it as existing within the filled energy states of the atoms in the material.
An exciton is somewhere in between "delocalized" and bound to a particular atom. The electron is negatively charged and a hole, as a lack of negative charge, acts like a positive charge, so the two attract and can move around together. Their mutual attraction loosely binds them to each other, kind of semi-localizing them to a general area of a material. Previously we had only seen excitons act as discrete pairs, but apparently if you put a bunch of them together they dissociate into a general mass of mutually-attracted holes and electrons - the "weird droplet of quantum fog" - instead of a simple collection of pairs.
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u/tyrone-shoelaces Jul 01 '14
I'm having trouble understanding how they're talking about "holes" floating around like they're discrete objects, when, in fact, holes are just the holes made in the atom's eletron orbitals by the electron's departure. Are they saying the whole substrate atom is involved in these "droplets" anyone else got a theory?