1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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

    User Avatar

    Staff: Mentor

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook