# Basic semiconductor theory.

Discussion in 'Homework Help' started by Urmi, Jul 31, 2010.

1. ### Urmi Thread Starter New Member

Jun 5, 2010
3
0
Hi everyone,I desperately need to understand a few concepts regarding semiconductors and how they basically work(referring to a p-n junction diode)..please answer my 4 questions...

1. What is it that actually stops the diffusion of carriers at the end of depletion layer formation?...is it that the stationary charges(e.g negative ions on the p-side) on either side repel the incoming charges?

2.When we say that in reverse bias,the holes in the P-side are attracted to the negative terminal (of the battery) at the P-side,we are basically saying that the minority electrons (that reside in the conduction band of the host semiconductor atoms in p-type crystal) move toward the junction...so it's exactly analogous to when the electrons from the n-side move in during depletion layer formation..is that right?

3.In forward bias, electrons and holes from close to the junction migrate a short distance and recombine. Since this continually happens, the external circuit appears like a steady current is flowing(my teacher told this in class)....does this mean that the electrons in the Conduction Band(of the atoms in the p side) move toward the junction?.....

(there'll also be some of these conduction band electrons that cross over into the n side, in order to fill in the vacancies created by electrons in the n side, which migrate towards the positive terminal,leaving behind holes when the forward bias is applied)

4.After electron-hole pairs are generated,do the electrons generated accumulate on the p-side...what does happen to them?

2. ### Fraser_Integration Member

Nov 28, 2009
142
5
1. Yes an in-built electric field opposes the flow of electrons.

2. Not sure what you're asking

3. Yes there is a much smaller drift current which acts in the opposite direction to the diffusion current.

4. This is similar to 1. The electrons at the p-type end of the depletion layer, and the holes at the n-type create the opposing electric field which limits diffusion.