Question

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

a) LED is a forward biased P-N junction diode made up of the direct bandgap materials, the positive terminal of the battery pushes the holes into the n region and negative terminal pushes the electrons into the p region, where they recombine with the majority carriers and will emit the light.

b) direct band gap material will be use to prepare the LEDs eg .. GaAs

c) spontaneous emission of the light. light is emitted in random directions

d) band gap of the material decides the color of the emitted light  

e) Feed back mechanism is required to make the Laser diode

F) stimulated emission is the phenomena used in the laser diodes