A short query on annihilation process

[NJunJie]

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?

 

[sokrates]

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.