I don't get why the electrons are able to go through the depletion layer when the negative terminal of a battery is connected to the N type.

Also If I connect the + terminal of the battery to the N type and the - terminal to the P type. The depletion layer will eventually be the whole diode, right ? I mean it expands till it's full ?

 

I don't get why the electrons are able to go through the depletion layer when the negative terminal of a battery is connected to the N type.

Also If I connect the + terminal of the battery to the N type and the - terminal to the P type. The depletion layer will eventually be the whole diode, right ? I mean it expands till it's full ?

When the PN junction is formed a electric field is created by the movement of electrons and holes to equalize (in equilibrium the device is overall neutral) the charge across the junction. This creates the depletion zone where no free charge carriers are available to allow for current flow. If we apply a external field across the diode (forward bias) of the opposite polarity of the internal diode junction field it will be neutralized to zero as the external potential is increased and the depletion zone will shrink in size to almost nothing. This allows the charge carriers to pass thru the junction easily. If the external field polarity is reversed (reverse bias) this will add to the internal junction field and the depletion zone will increase is size until the breakdown voltage of the device is reached or the depletion zone is the entire device active region.

 

Considering a point that is very far away from depletion layer, the potential at that point will be zero?
I think that because at that distance, the total electric field of two regions ( positive ions and negative ions) will be same as the electric field causing by sum of these ions.

And could you explain why the potentials in n and p region are constant?

 

Considering a point that is very far away from depletion layer, the potential at that point will be zero?
I think that because at that distance, the total electric field of two regions ( positive ions and negative ions) will be same as the electric field causing by sum of these ions.

And could you explain why the potentials in n and p region are constant?

I'm not sure what your question is. The static diode depletion potential is not something you can measure like a voltage from a battery, it's a barrier.

The bulk regions are doped for good conductance, any potential between the carriers within them would be neutralized by charge carrier movements to mainly cancel the electric field like in a metal conductor.