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LED vs plain diodes

  1. Jun 9, 2011 #1
    This is probably a stupid question but here it is:

    I am just learning concepts of LEDs. To me, it seems that there is no difference between LED and normal diodes. In normal diodes in forward bias, electrons come from n type and recombine in p type right? In this process photon should be emitted. Why we don't see that photon in normal diodes?

    It says here in my text book that same happen with LEDs. But what to you know normal diodes don't emit light and LEDs do :D
     
  2. jcsd
  3. Jun 9, 2011 #2
    Here is an explanation of how the light is created:
    http://en.wikipedia.org/wiki/Radiative_recombination

    The bandgap in LEDs are designed for radiative recombination, while the bandgap in diodes are not.
    More here:
    http://en.wikipedia.org/wiki/Indirect_band_gap

    This is also why a diode only has a voltage drop of about .65 volts and LEDs have voltage drops of generally around 2Volts or higher depending on the wavelength(color) they emit.

    Schottky diodes rely on an even different process called thermionic emission where the energy to cross a semiconductor-metal junction is based on the work function between the semiconductor material and a metal contact.

    Zener diodes work much the same as a normal diode however they are doped such that electrons can tunnel bacl through the semiconductor junction at a high enough reverse energy/voltage.
     
  4. Jun 10, 2011 #3
    Thank you for your explanation. I will have to go to QM to understand that, I was just wondering.

    Thanks
     
  5. Jun 10, 2011 #4
    All diodes are LEDs but you can't see the radiation.

    Solar cells are also LEDs. All diodes are solar cells and so are LEDs.
     
  6. Jun 10, 2011 #5
    Everything gives off radiation, I don't think that's the point or a good distinction.
     
  7. Jun 11, 2011 #6
    Its not the distinction I'm making. My statement stands on it's face as an optoelectronic statement of fact, not a resort to other physical principles.
     
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