Question

7. Diodes can emit light. a) In a light emitting diode, what must be done electrically to cause the diode to emit light? How is the light emitted? b) What feature of the band gap is needed to make the LED emit light without much energy going into heat? c) Is the light from an LED produced primarily by spontaneous emission or stimulated emission? d) What feature of the LED determines the color of the light? e) What addition to an LED is needed to make a laser diode? f) Is the light from a laser diode produced primarily by spontaneous emission or stimulated emission?

Answer 1

7 as To emit light electrical energy must be converted a to light energy which is done by combination of electrons and holes. The combination of election and holes causes electromagnetic radiation to emit and we have light energy. by The bang gap must be small such that election and holes combine with each other easily after apply small forward brasing. It is a spontaneous emission although simulated enuission is a laser pheonomenon. Height of barrier between election and hole - determines the colour of light. es For laser diode use PIN diode insead of PN junction . A PIN diode is a diode with undoped intrinste semiconductor region between a e and n type semiconductor : fl light from the laser diode is a stimulated emission, 7