I'm trying to get a better understanding of what the electrons and holes are doing when an NMOS is in the depletion region.

So far I understand that the holes in the P- substrate are attracted away from the gate, leaving negative ions behind. These negative ions now mirror the charge on the gate. This then forms a depletion region. Is this correct?

If it is, how are the negative ions being mirrored?

I also get that the Si02 acts as an insulator but now I don't even understand why it is there? If it wasn't what would happen?

I'm trying to get a better understanding of what the electrons and holes are doing when an NMOS is in the depletion region.

So far I understand that the holes in the P- substrate are attracted away from the gate, leaving negative ions behind. These negative ions now mirror the charge on the gate. This then forms a depletion region. No free charge carriers, meaning no current. Is this correct?

If it is, how are the negative ions being mirrored?

I also get that the Si02 acts as an insulator but now I don't even understand why it is there? If it wasn't what would happen?