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Thread: Semiconductors question

  1. #1 Semiconductors question 
    Forum Freshman fred91's Avatar
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    Hello to everyone,

    forgive my ignorance, I am studying in the third year of Physics and for now I've had only not very accurate information about semiconductors. I've been "explained" all the thing of the Fermi level that changes in type n and type p doping, but I can't answer a simple question. What has Silicon, for example, that distinguishes it from, let's say, Iron? Why in Silicon a "removed" electron moves like it was a positively charged particle, whereas in Iron it does not? It seems to me that semiconductors theoretical study occupies a separate part in Physics, but I don't get why they are so different. I mean, for what I know, Silicon as atomic number 14, Iron has 26, so what? Is it the geometrical shape of its lattice? Is it its electronic configuration?

    Thanks in advance, and sorry for wasting your time opening a new thread for such a simple question (even if it's not for me)


    Davis was questioning the increasing length of John Coltrane solos, and Trane answered "I don't know how to stop."

    Try taking the fucking horn out of your mouth.
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    Quote Originally Posted by fred91 View Post
    Is it its electron(fix) configuration?
    This is your starting point.


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    Forum Freshman fred91's Avatar
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    Hmm..you're evil Cloud! Ok, thanks I would have guessed it was something about the lattice! Interesting..
    Davis was questioning the increasing length of John Coltrane solos, and Trane answered "I don't know how to stop."

    Try taking the fucking horn out of your mouth.
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    Quote Originally Posted by fred91 View Post
    Hmm..you're evil Cloud!
    Always.
    Quote Originally Posted by fred91 View Post
    Ok, thanks I would have guessed it was something about the lattice! Interesting..
    Electron configuration - Wikipedia, the free encyclopedia

    I post a link since I'm not very good at explaining the things I have a poor understanding of myself. Others on here may be able to give good one on one guidance.
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    Forum Freshman fred91's Avatar
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    Thanks!

    Let's wait for some other clue
    Davis was questioning the increasing length of John Coltrane solos, and Trane answered "I don't know how to stop."

    Try taking the fucking horn out of your mouth.
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  7. #6  
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    Well iron isn't a semiconductor , it is a full conductor. Being a metal, its spare electron is in the outershell, practically allways.

    Now to the semiconductor .. The substrate has to be a non-conductor .

    Only where the dopant is just right, the energy levels of the from and to sites in the from and to atoms is equal, and the electron can tunnel from one atom to the other.

    The n type dopant creates the tendency for the electron to tunnell to the conducting shell. Why does it favour extra electrons?
    The p type dopant allows the electron to tunnel into a non-conducting shell, leaving a hole. Why does it favour holes?

    The conduction of holes is really tunnelling electrons ?


    In a BJT, the the rate of electron-hole pair creation by tunnelling is controlled by the base current, and then the electron-hole pairs move into the gap between collector and emitter, so the Emitter current is controlled by the base current.

    In a FET, the controlling field disables the conduction by removing the electrons or filling holes ,as the case may be.
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  8. #7  
    Forum Bachelors Degree Kerling's Avatar
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    A semiconductor is a material that has a bandgap between its valence band and conduction band. In short, there are no ' free' electrons in a semiconductor unless it comes in a different (exited) state. And then it does conduct. If you can cross or reduce the bandgap you can determine and regulate the conductance of a semiconductor.
    *bands are places of electrons. A conduction band is free electrons, valence aren't.
    In the information age ignorance is a choice.
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