Occurrence of inversion region for Depletion N-Channel Mosfet

Question

With an N-MOSFET has an N-doped channel between drain and source, it'll be conductive without any gate voltage applied. Consider you apply a negative charge to the gate, the resulting electric field pushes electrons out of the channel. As you add more charge, so many electrons will leave the channel that it undergoes inversion and effectively behaves as if it was P-doped, at which point the MOSFET stops conducting.

Would the inversion P-Doping region occur close to the oxide, or close to the interface between the N-channel (connecting the source and drain) and the P-substrate?

Answer 1

Usually applying a gate-to-source voltage in such a way that will make the gate negative relative to the source, the resulting effect is that the negative charge will force free electrons out of the channel. It will induce positive charges in the channel through the silicon oxide of the gate thus forming a carrier-depletion region in the silicon’s surface at the oxide-silicon interface. Since the current is due to majority carriers (electrons for an n-type material) the induced positive charges make the channel less conductive, increasing the channel resistance.