In an LED, is there a depletion zone as there is for a normal diode, and if there is, how do the electrons come into contact with the positive electron 'holes' to emit light?

Question

egenriether · Answer

Yes, the LED is no different than the non-light emitting type of diode except for the fact that they are direct band gap.  that means that the electrons in the conduction band can drop to the valence band in one step, not a cascade.  This energy change results in a high enough energy photon (E=hf) that it can be seen.  The electrons come in contact with the holes because when the diode is forward biased the depletion with becomes narrower allowing them to diffuse across the junction.  Remember the depletion width (space charge region) is there because electrons from the n side diffused over to the p side.  This left an electric field between them that builds up and eventually prevents further diffusion.  In forward biasing the diode you decrease this built in field, allowing for diffusion to occur again.

anonymous · Answer

Basically: when you put a diode the wrong way round and increase the voltage enough, the force due to the voltage will> electric field's force. If this is correct, I understand. Thanks!