Spintronic light emitting diode

  1. A new spintronic LED was invented by Utah physicists.

    http://unews.utah.edu/news_releases/utah-physicists-invent-spintronic-led/

    I thought that electron and hole suppose to recombine if electron is in exited state which means electron-hole pair is not in thermodynamic equilibrium with host material. But if carriers just injected in material, why they suppose to recombine? Does that mean that this new material becomes charged after recombination?
     
  2. jcsd
  3. UltrafastPED

    UltrafastPED 1,918
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    These are not excitons ... there are two different currents.
     
  4. Then why they do recombine?
     
  5. ZapperZ

    ZapperZ 30,167
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    That's an odd question because you are imposing the rule that only excitons recombine. This is false.

    When you excite an electron from the valence band to the conduction band, if the electron is not stable there, it will decay back into the valence band, i.e. recombine with another hole! This has nothing to do with creating an exciton, and the recombination doesn't require that the electron-hole pair is an exciton!

    Zz.
     
  6. They clam that injection of electrons and holes in semiconductor material from neighbouring materials leads to recombination of injected electrons and holes in this material. My question is: why does it exactly happen and if it is always a case? I assume that this injected carriers are not in excited state? And also, if we inject the same amount of electrons and holes in some material they should be in conduction band and there is charge neutrality. If electrons and holes combine later, injected electrons should fall to valence band (which could be full already) and holes (virtual carries of positive charge) should disappear. Therefore material should become negatively charged or what?
    And what if we inject electrons and holes in metal instead of semiconductor, will they recombine too?
     
  7. ZapperZ

    ZapperZ 30,167
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    Why not? After all, based on the statistics, there is a equilibrium population of the number (density) of electrons and holes in each band. By overpopulating, there are too many electrons and too many holes at that particular temperature. So why won't they recombine?

    Holes are equivalent to having a positive charge. Or in this case, there are electrons being sucked out of the valence band. So yes, they keep the charge neutrality.

    In what band would you inject these holes and electrons? Do you see a band gap to separate these two?

    Zz.
     
  8. Does increase of carrier density in some particular material always leads to their recombination? In any kind of material? For example article about thermoelectric effects says:
    I suggest that injections of carrier in some material is possible through conduction band only.
    If later theses carriers recombine then ingested electrons suppose to fall to valence band. But valence band is already full, usually. Where would they find a place?
     
  9. ZapperZ

    ZapperZ 30,167
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    Think about this case:

    You have electron and holes in thermal equilibrium in an intrinsic semiconductor at, say, 300 C. Now, let's say you can suddenly drop the temperature of the material to 50 C. Based on the statistics, there are now excess of electrons and holes in the material that cannot be supported by the temperature. What do you think will happen?

    Now look at the situation that we are dealing with. Isn't this the same thing? There is an excess of both charge carriers that cannot be supported by the statistics at that temperature! A fraction of the electrons in the conduction band will drop back to the valence band, as expected.

    Any evidence for this? What are you basing this on for metals?

    This is a head-scratcher. Are you making this up as you go along?

    Zz.
     
  10. Whether holes or electrons are injected intimately depends on the unique physics at the interface between two materials, how the bands bend , and the electronic structure of both bulk materials. The study of Schotky barriers is extremely complex and confusing, and I don't know if consensus on it's behavior has yet been reached.
     
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