What does the recombination current signify??

[kaps_nit]

As we start with the conductiviy property we find that electrons with higher energy moves to conduction band(e- gains energy from thermal or optical excitation). And only conduction band electron offers conductivity in general. Valance band electrons are not responsible for conductivity.

We also know that when recombination takes place, e- from conduction band comes down to valance band and recombines with holes and thereby give off energy as photons.

Now, take the case of transistors, say an npn transistor, here in the active region e- flows from emitter to base region and few of them gets recombined with holes, and leaves the base region as recombination current.

Now how to justify this apparent contradiction, as in this case e- in the valance band contributing in the conduction??????

 

[itzikhaim]

Hi,

Its not contradictory because recombination current in conventional diode/transistor and energy released when lowering to the c-band are not to be compared.

The 1st related to the classic physics of material in which e- at semi-cound. is moving in slow speed unlike the 2nd phenomenon which deals the conductivity movement of the e- near the speed of light.

The last is actually a qunatum area of electronic which being used at cellphones chips and other fast speed devices. (see the Quantum-well phenomenon and more).

Bye