A basic question about MOSFET...

Discussion in 'General Electronics Chat' started by Vorador, Jun 5, 2013.

  1. Vorador

    Thread Starter Member

    Oct 5, 2012
    87
    1
    Hi,

    When a positive potential is applied at the gate, electrons are attracted toward it and form a channel between the drain and source. I wanted to know whether these electrons that form the channel are "free" electrons or rather negative ions? I think they must be ions because prior to the formation of the channel, there must've been acceptor atoms in that region. So when the bias is applied and electrons fall into those atoms, they should become negative ions.

    If my guess is correct, are these ions mobile? i.e can they participate in conduction?

    Thank you! :)
     
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    I don't know nothing about semiconductors physics. But I suspect it must be a free electrons.
     
  3. tshuck

    Well-Known Member

    Oct 18, 2012
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    Ions are static, making up the crystal lattice structure and cannot move.
     
  4. crutschow

    Expert

    Mar 14, 2008
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    The only moving charge in semiconductors is electrons. Even when we talk about positive "holes" in P-material it's still really the electrons that do the moving.
     
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  5. circuitfella11

    Member

    May 10, 2013
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    negative ions/ electrons.. they're the only ones that does move.. they regarded p-materials as holes, they don't move, but it is where electrons pair up to stabilize it.. the material is so little in the gate..the bias applied turns the mosfet on or off..so the bias applied makes the reaction on the material to let pass or not let pass from source to drain.
     
  6. Vorador

    Thread Starter Member

    Oct 5, 2012
    87
    1
    That answers one of my questions, crutschow. I also wanted to know what the channel is "made" of. Neutral atoms with a free electrons, or atoms with an excess of electrons (negative ions)? And why doesn't the current start flowing until the "channel" has formed? I mean, in a semiconductor P-N diode, electrons move from the N region into the P region. So what stops electrons from going from the N region, through the P region substrate and to the other N-region in a MOSFET? Why is an "N channel" that connects the two separated N-regions necessary to make the electrons flow in MOSFETs?
     
  7. crutschow

    Expert

    Mar 14, 2008
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    The channel is made of the material in the substrate which is opposite the MOSFETs channel type. This explains it better than I could.
     
  8. Vorador

    Thread Starter Member

    Oct 5, 2012
    87
    1
    Thank you.
     
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