I wasn't certain to post this in chemistry or physics section.

I was reading the wikipedia article on "Carrier generation and recombination" and in the second paragraph it says something that I wish to understand.

It says "The electron-hole pair is the fundamental unit of generation and recombination, corresponding to an electron transitioning between the valence band and the conduction band." I am curious what does fundamental unit mean in this context.

I know fundamental units in The S.I. system are the base units for the physical quantities of length, mass and so on. The fundamental units depend on the subsystem you use as well. It can be the mks or cgs. But the fundamental unit is what the other units are based from. So I understand that they are created and can differ between the system that is used.

But I learned in physics class that a fundamental unit is just something which all other values are generated from. My physics teacher used an analogy of net wealth = n*(p), where n is a whole number and p is a fundamental unit. Which he told us would be the cent. So net wealth is a whole number multiplied by cents. And any wealth can be generated from that fundamental unit. Additionally, we learned that q = n*(e), where q is charge, n is a whole number and e is the fundamental unit of charge -- an electron.

So if I am correct, all other values must be whole number multiples of the fundamental unit, thus it is impossible to have a value less than the fundamental unit. Simply you can have a certain number of the fundamental unit.

So can I say that (carrier charge) = n*(h), where n is a whole number and h is the fundamental unit of carrier charge, an electron-hole pair.

I apologize for any extreme errors in my reasoning, I don't even understand what an electron-hole pair is really. I read online that an electron hole is the absence of an electron in a location in which it could exist.

Thank you,

  • $\begingroup$ It just means that when you move an electron from the valence to the conduction band, you make a free electron and a hole. They come as a 'matched pair' - you can't make just one or the other. $\endgroup$ – Jon Custer Dec 31 '15 at 4:06

A fundamental unit doesn't always mean any system of units like the SI unit system. A unit is synonymous to unity (i.e. 1). In any measurement system like the SI system, the entities like meter, second etc are fundamental; they are the unity. You can have nothing smaller than a meter or a second. You can have multiples of them, even non-integral multiples.

So simply put, the electron-hole pair generation isn't any system of units, and it would make no sense to call the electron-hole pair as a fundamental unit of carrier charge.

What the article meant was that all electrons that jump from the valence to the conduction band are generated by the electron-hole process, and thus that generation process is the fundamental unit of generation - for every $n$ electrons that jumped from the valence to the conduction band, there must be $n$ electron-hole generation processes.

But your idea that *Carrier Charge = n * Fundamental unit of Carrier Charge* is indeed correct; it jus has nothing to do with the process of electron-hole pair generation.

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