Semiconductor physics (electron-hole lifetimes)

[big man]

OK I'm just having a bit of trouble getting my head around this concept. I'm doing a small talk on it as a mini-assignment for solid state, and so I really need to understand this.

A semiconductor in thermal equilibrium
Now I know that the recombination and generation rates are equal in this case. So this means that the net charge carrier density remains constant.

MY QUESTION
But what is the significance of that? Are there some cases where you'd want it to be constant and then for other applications you'd want excess charge carriers? I mean I assume that if you were wanting a semiconductor to act more like a metal conductor then you'd want to increase the level of excess charge carriers?

Excess charge carrier lifetimes
The recombination lifetime measures the period of recovery of carriers from the perturbed state (conduction band) to the equilibrium state (valence band). The generation lifetime refers to the time associated with the generation of charge carriers.

MY QUESTION
So essentially, if you wanted to have a good conducting semiconductor would you aim to have a long recombination lifetime and short generation lifetime?

I know these are stupid questions, but I'd appreciate any help.

 

[Jhero]

Thank you for your questions regarding semiconductors in thermal equilibrium. As a scientist in the field of solid state, I am happy to provide some clarification on these concepts for you.

Firstly, the significance of the equal recombination and generation rates in a semiconductor in thermal equilibrium is that it allows for a stable and constant net charge carrier density. This is important for many applications, such as in electronic devices, where a consistent flow of charge carriers is necessary for proper functioning.

However, there are cases where having excess charge carriers is desirable. For example, in photovoltaic cells, excess charge carriers are generated by light and are necessary for the conversion of solar energy into electricity. In these cases, the semiconductor is intentionally designed to have excess charge carriers.

In terms of excess charge carrier lifetimes, a longer recombination lifetime and shorter generation lifetime would indeed result in a better conducting semiconductor. This is because a longer recombination lifetime means that the charge carriers have more time to move through the material and contribute to conductivity, while a shorter generation lifetime means that new charge carriers are constantly being generated to maintain the flow of current.

I hope this helps to clarify these concepts for you. Please let me know if you have any further questions or need more information. As a fellow scientist, I am always happy to assist in any way I can.