Capacitance of a forward biased diode

[akhil123]

How does a forward biased p-n junction display capacitive effect? I understand that a reverse biased diode can exhibit capacitance with the depletion region acting as a dielectric, but in a forward biased junction, depletion region does not exist,so how does it show capacitive behaviour?

 

[torquil]

I may be wrong because I don't know a lot about the physics of semiconductors, but a sentence on the wikipedia description of a forward biased diode struck me as relevant to your question.

Ok, when the diode is forward biased, current still doesn't flow, right. So there is a potential difference between each part of the diode, like in a capacitor. In addition it says on the wikipedia page that "This reduces the width of the depletion zone.".

So it seems to me that as long as the foward bias is not too large, there is still a depletion zone between the N and P parts, and there is a potential difference across it. So it should have some capacitive properties, right?

Ref:
http://en.wikipedia.org/wiki/P-n_junction#Forward_bias

Torquil