# what is the origin of minority carrier in semiconductor?

I am analyzing particular type of radiation detector which is used in medical imaging device.The depletion layer and minority carrier plays a big part of the charge collection process, specially the reverse current and thickness of the depletion layer directly effect to the noise of the generated radiation signal. The reverse current is mainly generated due to minority carries in the p or n area. My question is what is the exact origin/s of minority carriers. Is it only due to thermal excitation or are there many other factors other than thermal excitation and which is more significant?

Thanks

• I don't have an answer, but I do have a thought. Impurities of the "wrong" type ought to produce minority carriers. I believe, without being able to justify it, but with some experience, that thermal excitation will dominate in common practical devices. I think that in order for a device to work properly, the density of minority carriers has to obey the "simple" version of the usual model. – garyp Mar 13 '18 at 0:00
• It is thermal equilibrium. It is the mass action law, like the concentration of OH$^-$ in solutions of acids. There could be many factors, exact mechanisms do not affect the outcome. – Pieter Mar 13 '18 at 7:18

The external source like $\textbf{light}$ with energy more then energy gap of material will provide additional minority carriers. You can also $\textbf{inject}$ minority carriers using two junction "pn-np" first polarized in forward bias will provodes electrons to second polarized in reversed bias as minority carriers - this is the main principles in bipolar transistors pnp or npn.