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Radioactive recombination occurs when an they ar eelectron in the conduction band combines with holes in the valence band and energy is emitted in form of photon

lamda=hc/energy gap

semiconductor energy gap lies btw ----- 1.78 to 3 ev

visible region wavelength - 0.38 to 0.78

get and si has 0.7 and 1.1 ev so not suitable

DIRECT AND INDIRECT BAND GAP

the alignment of the maximum energy with minimum energy is properly allignd with respect to momentum

they are unaligned with respect to momentum

direct recombination takes place as the energy released I equal to the energy difference btw the recombination particles.

first due toimproper momenta alignment energy is conserved and when they are properly aligned then recombination takes place

probability of recombination is high

low

efficiency factor is high so used in lenses

efficiency factor is low

ex=== GaAs (galliumarsenide)

ex===ge and si

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LED -------

acronym for light-emitting diode

p-n junction with forward bias.

principle - injection electroluminscene

electroluminscene = when visible radiation radiates whe low V DC is applied to a suitably doped on junction.

materials used ===

Ga phosphide

Ga arsenide

Ga nitride

aluminum gallium phosphide

al Ga nitride