I can not explain my question concisely as I am beginner and I have difficulties with chemical and mathematical terms, so I will discuss my logic from the beginning foolishly.
What I understand about potential difference
The basic electronic says a source voltage is the result of a potential difference between its poles. With that I understand that a battery of 1.5V has a positive terminal with 1.5 volt charge and a negative terminal to 0 volts of charge. The nature of the material excess electrons on the negative pole tend to go for the positive pole until they neutralize. When this happens the battery will have 0.75V at each pole and the potential difference will be 0v. Correct? I am not sure.
What I understand about diode
A diode is a semiconductor electronic component divided into two poles, one negative and one positive so with a potential difference between them; It is separated by a resistive layer between the poles. When a diode is connected to battery directly (negative diode with negative source) etc, free electrons on the negative side of the battery repel the electrons free from the negative side of the diode to destroy the resistive layer and the current flow through the circuit.
What I can not understand
Let's say I have a source with 0 volts in its negative pole and a diode with -7 volts in its negative pole. Logically, the electrons on the negative side of the diode should go to the negative side of the source and thereby increase the depletion layer in the diode even when polarized directly to the source.
Another example ... let's say I have a diode with upside potential of 5V connected to the positive side of the battery that has 20 volts potential. In this scenario, why the electrons of the diode will not meet positive side of the supply to the increasing depletion layer?
I think it got a little confusing but I hope someone understands me and can help me.