Recombination mechanisms

Although electrons and holes are excited by light absorption, they can recombine when they meet each other in the lattice.  This means they will lose their mobility and be fixed into molecular orbitals within the lattice of the semiconductor again.

Radiative recombination is the 1st type of recombination, where after the electron and hole recombine, energy is released as a photon, which has the energy of at least the band gap.

Auger recombination is the 2nd type of recombination, where the recombination energy is transferred to a nearby free electron in the conduction band.  The free electron will be excited to a higher energy level, and then lose its energy as heat, heating up the semiconductor.

SRH recombination is the 3rd type of recombination, and it occurs due to defects in the semiconductor, which cause energy states to develop in the forbidden band gap.  These energy states can trap electrons at a lower energy level than that required to cross the band gap, and electrons can lose this energy when they meet and recombine with freely moving holes.

Reference:
2.3.3 Transport of Charge Carriers, Delft University of Technology, https://www.youtube.com/watch?v=2EhJh3BQvB0