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Homework Help: L.E.D's and the photoelctric effect

  1. May 4, 2005 #1
    hello - i feel confident that i understand the principles of how L.E.D's work. I can grasp the concept of the depletion zone and how this leads to conduction in one direction.

    But how does light from an ordinary filament lamp cause a voltage in an L.E.D to be produced when the L.E.D has no obvious power supply?

    I know of the principles of the photoelectric effect and realise it has something to do with this but need a concise explanation of how the voltage is produced.

    i have been discussing this with sum1 else and have come up with this explanation:

    light from the lamp when incident on the semiconductor in the L.E.D causes valence electrons in the n type semiconductor to be released into the conduction/ depletion layer. these are attracted to the p type semiconductor and they move into the 'holes'. this causes a drop in energy level for the electron which is called relaxation and causes light to be emitted.
    this process means that a current is flowing from the n to the p type semiconductor which means that a voltage is present in this mini - circuit.

    now the fact that white light has a low photon energy means that if it were the photoelectric efect that causes this process - the material in the L.E.D would need to have a low work function or sum other proerty that allows this to happen.

    anyone who can correct any details - add more information - or completely change the explanation to the question - please feel free

  2. jcsd
  3. May 4, 2005 #2

    Doc Al

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    Staff: Mentor

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