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Thread: P and N type semiconductors

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    Flak Monkey! Dorza's Avatar
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    P and N type semiconductors

    Not sure if this is the right place but any way..

    Im about to do an article about these on my site and as a result i have been reading up on the subject, however i would like to confirm one small bit of information...

    With N type the impurity added has 5 electrons and the P type has 3 electrons. Now what I'd like to know is, do these electrons "join" the silicon/germanium electrons (which have 4 electrons in a crystal structure) leaving 1 electron free in both the N and P Types. In the P-type would this free electron be called a hole? Im finding it quite a complex subject to write about especially as im not that great with this kind of chemestry/Physics.

    BTW: what are valance electrons. Im reading alot about them.
    Last edited by Dorza; 24-08-2004 at 01:47 AM.

  2. #2
    Administrator Moby-Dick's Avatar
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    *Moby racks his brains back to Electronic Materials at Uni about 4278256 years ago*

    to "dope" the material to make it n type or p type you would use a matieral that has an extra valcence electron ( N type ) or has one less (P type ) This impurity is forced into the electronic strucutre of the substrate material ( Si or Ge ) In the case of N type materials , you have given material which usually has no free electrons for conduction some free electrons so that it can start to conduct. P type material has been doped with a defeciancy of electrons. This lack of an electron is the "hole" which can move through the structure in the same way that an electron can ( remeber an electron carries a negative charge )

    A valence electron is an electron in the highest energy level , furthest from the nucleaus that is able to take part in elctronic interactions.

    I'm sure there are some huge flaws here , but its a good start.
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    Cute & Fluffy GreenPiggy's Avatar
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    yep, you essentially turn your material into either an acceptor of electrons(using trivalent doping) or a doantor(using pentavalent doping) by adding electrons or holes to the fermi layer of electrons.
    Typical pentavalent doping materials are: antimony, arsenic or phosphorous
    Typical trivalent doping materials are: boron, aluminum or gallium
    Do you remember high school Chemistry when they taught about electron shells?
    Valence electron is just another term for an electron in the outer shell.
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    Flak Monkey! Dorza's Avatar
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    Cool, thanks for your help. So essentally then the imputury and the slicon join bond together and the electrons left (be it the 1 Silicon in the P type and the 1 extra in the N-type) are able to roam around which allows for a curent to flow. Is that right?

    EDIT: in the N-Type there are too many electrons so one is thrown out and in the P-Type the one that has no partner goes "looking" which leaves a hole in the atom for another "looking" electron. Im just trying to c if i understand it
    Last edited by Dorza; 24-08-2004 at 01:06 PM.

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    Cute & Fluffy GreenPiggy's Avatar
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    Erm..not quite.
    The point of doping something is not to make it easier for current to flow through the material but to make it easier for current to flow in and out of it by making it either an attracter or repeller of electrons.
    The most useful application is by making what we call a P-N junction by slapping the two types next to each other, thus making effectively a one way path for electricity flow.
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    Goron goron Kumagoro's Avatar
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    Haha are you sure you should be writing an article on semiconductors when you dont really know whats going on?

    I dont think there is anything else i can say which hasnt already been said. Acutally i cant even work out what you understand at this point as what you originally said is incorrect maybe a review of what you understand and want to know will help you.

    I just hope you dont want to go into electron band bending and direct & indirect band gaps.

    uhhhhh im having electronic devices flash backs.. cha'mone

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    Cute & Fluffy GreenPiggy's Avatar
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    Quote Originally Posted by Kumagoro
    I just hope you dont want to go into electron band bending and direct & indirect band gaps.

    uhhhhh im having electronic devices flash backs.. cha'mone
    yeeuuch. stop that
    Knight 1: We are now no longer the Knights who say Ni.
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    Other Knights: Shh...
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