I was reading the answer from placeholder and re-posting his excerpts from an answer.

I didn't understand the following points well:

the channel has p-dopants in it which when the voltage is applied get ionized by the E-field. This is what establishes the channel.

Original Question: Mosfet Depletion Region?


  1. What do you mean by ionisation of p-dopants by an electric field
  2. Can you explain more on "This is what establishes the channel"
  3. And lastly,

The charge that is in the channel that equates the gate charge is due to the uncovered acceptor atoms (p-dopants).

Can you explain this again? When you say channel in the above line, are you referring to the regions immediately beneath the oxide layer on the surface of the semiconductor (semiconductor-oxide interface)


1 Answer 1


This is incorrect. The body (sometimes called 'bulk') has acceptors (dopants; impurities) which create holes. These acceptors are ionized (under normal conditions) as soon as they are implanted and remain ionized. The holes make the body p-type.

When an E-field is applied (from the gate electrode), it repels the holes and with sufficient field (enough to bias the channel to the threshold voltage), electrons are attracted to the interface and form a channel.

  • \$\begingroup\$ Perhaps a bit misleading regarding ionization of the acceptors. The electrons aren't really stripped from them as in that they leave the material, they're just more "free" to roam inside the semiconductor so it is quite easy to ionize them with an electric field. \$\endgroup\$
    – Sven B
    Oct 23, 2022 at 22:48

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