B What is the purpose of the depletion region in P-N junction semiconductors?

[Praveen1901]

I'm new to semiconductors.

While I was studying types of biasing in semiconductors, here's what I read -
'In forward biasing, the width of the depletion region is reduced.'

Here's what I thought -
Since the potential barrier is reduced in the junction due to external potential, the diffusion Current directed from p to n side should increases, leaving behind more -ve charge on P side and more +ve charge on the n side, and thus increasing the depletion region.

Please correct me where I'm wrong :)

 

[Zaya Bell]

First, by saying semiconductor, I think you really mean PN junction diode.
Now, drift current is the tiny amount of current that flows when hole/electrons move from where they are highly concentrated to a region of lower concentration. This doesn't say anything about due to application of electric field. Any current that flows due to electric field is drift current. Now you may say that this drift current may however still cause the depletion layer to widen. No, it won't.
You can consider it this way, if I have such a PN Junction diode and I forward biase it, the little electrons at the P region will get attracted to the positive terminal of the battery/power source. But immediately, this electrons will be replaced by other electrons from the N region since there are no more electrons in P to prevent such crossing over (remember the electrons at the P region was formerly preventing more electrons from crossing, which is what creates the layer in the first place).This is still a diffusion current. This crossing over would have kept the barrier independent of voltage applied (imagine manually, like by hand, removing the electrons at the P region, the diffusion will still happen) but as you said the applied electric field opposes the barrier field until it goes to zero then drift current flows.

You can also consider it that the barrier creates a large resistance (almost open circuit) at that drift current can't flow. Only diffusion can.

 

[darth boozer]

You are misunderstanding what the depletion region is. See https://en.wikipedia.org/wiki/Depletion_region