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P-Type semiconductor. Which band does ''hole'' current occur in?

Discussion in 'Electronics Homework Help' started by george2525, Sep 1, 2015.

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  1. george2525

    george2525

    170
    0
    Jan 30, 2015
    Hello,

    I have often been confused regarding majority (hole) carriers in the P-type part of a diode etc. I have ripped the following from hyperphysics.com for a reference.

    I understand this diagram apart from -

    Which band - conduction or valance - does ''hole current'' occur?
    If valence electrons fill the new energy states (representing group III I assume) as shown in the diagram they leave holes in the dark grey valence band, right.

    So does this mean that for hole current the light grey conduction band does NOT come into play and that current occurs in the valence band AND the new (Group III) energy states introduced by doping.

    I have yet to see an explanation of this referring to bands specifically so would much appreciate if anyone knows the answer.

    I think the term ''conduction band'' makes me think that perhaps I am wrong because it implies that conduction always occurs in this band and NOT in the valance band.

    Best wishes, G






    P-Type Band Structure

    The addition of acceptor impurities contributes hole levels low in the semiconductor band gap so that electrons can be easily excited from the valence band into these levels, leaving mobile holes in the valence band. This shifts the effective Fermi level to a point about halfway between the acceptor levels and the valence band.
    [​IMG]
    Electrons can be elevated from the valence band to the holes in the band gap with the energy provided by an applied voltage. Since electrons can be exchanged between the holes, the holes are said to be mobile. The holes are said to be the "majority carriers" for current flow in a p-type semiconductor.
     
    Last edited by a moderator: Sep 2, 2015
  2. Ratch

    Ratch

    1,094
    340
    Mar 10, 2013
    Hole current occurs in the valance band.


    Hole current in the valance band will not occur until the electrons in the valance band jump to fill the holes just above the valance band. Otherwise there will be no holes in the valance band to conduct current.

    The conduction band conducts electrons, the valance band conducts holes.


    Conduction occurs in both bands if the correct charge carriers are present. In the attachment you included, no conduction in the valance band will take place unless the electrons in the valance band jump into the holes just above the valance band. At room temperature, all those holes above the valance band would be filled with electrons, thereby leaving the valance band with plenty of holes.

    Ratch




    P-Type Band Structure

    The addition of acceptor impurities contributes hole levels low in the semiconductor band gap so that electrons can be easily excited from the valence band into these levels, leaving mobile holes in the valence band. This shifts the effective Fermi level to a point about halfway between the acceptor levels and the valence band.
    [​IMG]
    Electrons can be elevated from the valence band to the holes in the band gap with the energy provided by an applied voltage. Since electrons can be exchanged between the holes, the holes are said to be mobile. The holes are said to be the "majority carriers" for current flow in a p-type semiconductor.[/QUOTE]
     
    LvW likes this.
  3. george2525

    george2525

    170
    0
    Jan 30, 2015
    Thanks Ratch, you have saved the day again
     
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