Carriers in Ag. Are these excited conduction electrons?

Smythe

I am attempting to solve a question which asks about the carriers in Ag.

Is the use of the word 'Carriers' simply another way of saying excited conduction electrons?

Thank you.

citrus burst

Yup. Silver's a metal so all the charge carriers are electrons. For metals the conduction band and valence band overlap so the electrons don't have to be excited to conduct.

If this was a semiconductor like germanium or silicon the carriers would have to excited and include both electrons and holes.

Labarbapostiza

Smythe wrote: »

I am attempting to solve a question which asks about the carriers in Ag.

Is the use of the word 'Carriers' simply another way of saying excited conduction electrons?

Thank you.

Yes.....but there's a weird thing about the noble metals; the conduction electrons are not in the outer orbits. So, they are chemically unreactive (I don't know the actual chemistry term for that, but they don't react with much), but they can conduct electricity, because the electrons in the inner orbitals are able to flow........Someone else probably has a better explanation; and I'd like to hear it too.

Labarbapostiza

citrus burst wrote: »

If this was a semiconductor like germanium or silicon the carriers would have to excited and include both electrons and holes.

Silicon and germanium need to be doped with impurities to conduct. The holes are from the doping atoms. The doping allows them to semi-conductor; hence they are called semiconductors.

citrus burst

Labarbapostiza wrote: »

Silicon and germanium need to be doped with impurities to conduct. The holes are from the doping atoms. The doping allows them to semi-conductor; hence they are called semiconductors.

This is way off the mark. Silicon and germanium conduct without dopants, just not very well. Holes exist within intrinsic semiconductor materials.

Labarbapostiza

citrus burst wrote: »

This is way off the mark. Silicon and germanium conduct without dopants, just not very well. Holes exist within intrinsic semiconductor materials.

No....You're not even wrong.

Silicon by itself is an insulator. The only way you'll get it to conduct electricity is to tear it's crystal structure apart. Literally burn it.

For it to become a conductor, the silicon needs to be either negatively doped or positively doped. In positive doping, in the crystal structure there are electron holes, the doping material interrupts the crystal structure of silicon, leaving holes. That is holes that can accommodate an electron. This allows electricity to flow through the p-doped silicon, without burning its' crystal structure. Negatively doped silicon, on the other hand, has excess electrons. These can allow electricity to flow without burning the silicon crystal structure. The materials are solid substances, where the impurities create interruptions in the crystal structure. They can conduct electricity and remain solid.

Now the magic of semiconductors: If you place two pieces of doped silicon together that is a piece of n-doped, with some p-doped, you'll get a semiconductor junction. At the junction you'll get a depletion layer. That's when some of the excess electrons in the n-doped material hop into the holes in the p-doped material. The depletion layer is more like pure silicon, in that it is an insulator. This is a typical semiconductor diode.

And why they're called semiconductors. Remember the n-doped, and p-doped silicon can conduct electricity by themselves, but when placed together the pesky insulating depletion layer forms.

If you get a battery and connect the positive terminal to the p-doped silicon, and the negative to the n-doped, the configuration is in forward bias. Electrons from the negative terminal can push the excess electrons towards the junction - this shrinks the insulating depletion layer, until it's gone and you have both pieces of doped silicon conducting (there is some added magic to this, there's a minimum voltage that must be applied to completely shrink the depletion layer. This allows for reliable logic in semiconductor electronics)

Now, if you put the diode in reverse bias. The negative terminal to the p-doped, and the positive terminal to the n-doped. Electrons rush into the holes in the p-doped, turning it into an insulator. The way this actually works though is the insulating depletion layer between the two semiconductors grows.

So, what we have is a piece of material that can conduct electricity one way, but cannot conduct it in the opposite direction. A semiconductor.

Use three pieces of material, n-p-n or p-n-p, you can use three terminals and now you have a transistor, operating under the same principles as the diode. And there are other configurations of the material, that allow a variety of different diodes and transistors, that do all kinds of wonderful things.....In fact they do everything. It's the fundamental principle by which your computer works.