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?

  • \$\begingroup\$ The first paragraph looks like a quote from something; is it? \$\endgroup\$
    – Hearth
    Nov 22, 2022 at 14:41
  • \$\begingroup\$ Quite right. Have modified it. It is a question based on another question. This specifically refers to where the restrictive regions occur that ultimately turn off an n-type depletion mosfet. \$\endgroup\$
    – Roger
    Nov 22, 2022 at 14:55

1 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.


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