L.E.D's and the photoelctric effect

[ryan750]

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 realize 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

thanks

 

[Doc Al]

Followups here: https://www.physicsforums.com/showthread.php?t=74292

(Please do not double post!)

 

[thepatientmental]

for the explanation! You are correct in your understanding of the photoelectric effect and how it relates to the production of voltage in an L.E.D. The key factor here is the band gap energy of the semiconductor material used in the L.E.D. This band gap energy is the minimum amount of energy required for an electron to move from the valence band to the conduction band.

When light from the filament lamp hits the semiconductor material, it provides enough energy for some of the electrons in the valence band to jump to the conduction band. This creates a flow of electrons from the n-type to the p-type layer, resulting in a voltage difference. This voltage difference is what powers the L.E.D.

The reason why white light, which has a lower photon energy, can still produce this effect is because the semiconductor material used in L.E.D.s is specifically chosen to have a low band gap energy. This allows the electrons to easily jump to the conduction band with the energy provided by the light.

I hope this helps clarify the process of how L.E.D.s use the photoelectric effect to produce light and power. Let me know if you have any further questions or need more clarification.