A short query on annihilation process

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The annihilation process in semiconductors involves the recombination of excited electrons in the conduction band with holes in the valence band. Although electrons can gain enough energy to move into the conduction band, they may still experience forces that pull them back to the valence band, leading to recombination. This process is typically in equilibrium, where each recombined electron is replaced by a thermally excited one on average. The time constants for recombination and generation are generally slower than the transport times of charge carriers, which is why they are often overlooked in practical applications. For a deeper understanding, refer to Pierret's "Advanced Semiconductor Devices."
NJunJie
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How does this annihilation process play in semiconductors?
Initially i thought that as long as the an electron gets enough energy to move into conduction band (in an energy diagram) - it will move and wander within the Conduction band. However, i have a slide notes about annihilation that talks about recombination.
How does this comes to play? - Does this means that although the electrons gets excited into Conduction Band - still there is some energy in the electron that will pull the electron back to Valence Band?
 
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Normally, recombination and generation are in equlibrium in a semiconductor... For each electron that's recombined, another one would be thermally excited "ON AVERAGE"...

Normally the time constants for such processes are way slower than transport times so they are ignored most of the time.

For a comprehensive analysis, See Pierret - Advanced Semiconductor Devices.
 
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