Why is there reverse current in diode equation?

[satominari]

When deriving diode equation, it is assumed that there's no drift.
But still, in the result, we have a reverse current which is a drift...
I don't get where this comes from.

 

[leader]

Even when the diode is not biased there is a diffusion current from n-type material to the p-type material because of difference in electron concentrations similar to the hole diffusion current from p-type material to the n-type material. These opposite currents carry like charges accumulating on he edges of the depletion zone while canceling each other within the depletion zone. These diffusion phenomenon is essential for the operational principal of the diods.

 

[leader]

Yes. So created depletion zone is responsible for drift currents. Imagine the photoelectric effect for photo diods. Photons falling on the depletion zone of the diods liberate electrons biased by the electric fields already created by the diffusion currents. In a photo diod circuit, an external reverse bias is also applied to increase the photo diot current (signal).

 

[Svein]

You will most likely have a temperature-dependent leakage current. Also see post #3.

 

[satominari]

You will most likely have a temperature-dependent leakage current. Also see post #3.

Thanks for the reply. But could you explain or give me a link about temperature dependent leakage current? Thank you so much!

 

[cnh1995]

Thanks for the reply. But could you explain or give me a link about temperature dependent leakage current? Thank you so much!

https://en.m.wikipedia.org/wiki/Saturation_current
There are many more.

 

[Svein]

Thanks for the reply. But could u explain or give me a link about temperature dependent leakage current? Thank you so much!

See for example http://www.onsemi.com/pub/Collateral/1N4001-D.PDF, page 3 for a real-world example.

 

[marcusl]

The minority carriers being discussed above are generated by random thermal generation of electron-hole pairs. The generation rate is temperature dependent.