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What happens after I give energy more than forbidden gap

  1. Jan 3, 2016 #1
    Hello guys I have a question about semiconductor, suppose I have a semiconductor say silicon at room temperature. The forbidden energy gap in case of Silicon is 1.1eV. Suppose I give I introduced an electric field(or by any other way give energy) which could give each electron an energy more than 1.1. What will happen then?

    I suspect with an energy of say 1.2eV only few(relatively) electrons will go to conduction band breaking the valence bond. Because for other electrons in valence band the gap will be even more than 1.1eV. As forbidden gap is defined as the difference between highest energy level of valence band and lowest (available) energy in conduction band. So it should not take equal energy to take electrons from the different valence bond . in other words it would take different energy to break different bonds. Am I correct?


    My other question is what will happen if I give very high amount of energy so that I am successful in breaking all the bonds between silicon atoms? Will it reduces to isolated atoms then?

    Regards
     
  2. jcsd
  3. Jan 3, 2016 #2

    mfb

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    Staff: Mentor

    An electric field is energy per distance for electrons, electrons that cannot move have problems to "use" the electric field. Very high fields allow direct tunneling, but long before that you get avalanches from individual electron/hole pairs that exist at room temperature.
    If you heat silicon, it will melt and then boil, sure.
     
  4. Jan 3, 2016 #3
    Thank you :) Sorry I wrote in a an unclear way, we'll what I want to know, what will happen after Avalanches, will all the covalent bonds break? Of yes how will the Silicon as sold sustain with all bonds broken? Breaking all bonds should reduce silicon solid into isolated atoms or something.

    In short I want to know what is the state of Silicon during Avalanche in terms of free electrons in it and the states of most of its covalent bond.

    I also want to know how will things become after removal of electric field from an Avalanched silicon again in terms of free electrons in it and the state of most of its covalent bonds. Will it recover from all of its broken bonds and become same as it was before it gone through Avalanche?

    What is meant is to heat to 900 °C given its melting point is above 1400°C.
     
  5. Jan 3, 2016 #4

    mfb

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    Those electronic effects happen with a tiny subset of the electrons in the material, they don't influence the crystal structure as a whole.
    Silicon with avalanches is still a silicon crystal, just with some current in it.

    Extremely intense laser pulses are an exception, where you can vaporize some material directly. There the band structure does not matter any more.
     
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