The recombination process is the inverse of generation of free electrons and holes. So, free electrons in the conduction band or in lumolevel fall in a hole in the valence band or a homolevel. There are different recombination mechanisms depending on energy band structure of the material the hole concentration p and the electron concentration n, the trap density Nt and their position in the energy gap.

There is radiative band -band recombination with the rate r is proportional to pn, which is a second order recombination as the recombination rate is a product of the two concentrations. It is also called bi molecular as both particles are engaged.

There is recombination band band via traps which is a nonradioactive recombination. It can be proportional to either p or n or np. It can be first order or second order or mono molecular or biomolecular.

Auger recombination where the rate r is proportional to nnp or ppn which is third order.

All these re combinations can be considered nongeminate recombination as only the free electrons and holes are considered involved.

Geminate recombination occurs when weakly bound electron hole pairs recombine with each other.

More about geminate and nongeminate recombination in the link:https://www.researchgate.net/post/What_is_the_meaning_of_geminate_and_non-geminate_recombination_in_solar_cells#view=5b8ba5d7979fdc70122d7441

Best wishes

plus, geminate and nongeminate recombination as well

recombination of an ion with an electron can proceed in a direct process called radiative recombination in which a photon carries away the excess energy released by binding the initially free electron to the ion.

Dielectronic Recombination (DR) of an ion with an electron proceeds in two steps. The first step is  capture of the initially free electron with simultaneous excitation of a bound electron.  This is time-reversed (single) Auger decay and can only occur if the energy of the free electron plus the binding energy after its capture matches the excitation energy of the initially bound electron. In the second step the reduced charge state of the ion is stabilized by emission of at least one photon.

Higher-order recombination processes of an ion with an electron proceed via capture of the initially free electron with simultaneous excitation of two or more bound electrons. The resulting highly excited ion with its charge state reduced by 1 unit then stabilizes by emission of photons.

Let me know if this answers your question.

Thanks a lot for your detailed answer

The recombination process is the inverse of generation of free electrons and holes. So, free electrons in the conduction band or in lumolevel fall in a hole in the valence band or a homolevel. There are different recombination mechanisms depending on energy band structure of the material the hole concentration p and the electron concentration n, the trap density Nt and their position in the energy gap.

There is radiative band -band recombination with the rate r is proportional to pn, which is a second order recombination as the recombination rate is a product of the two concentrations. It is also called bi molecular as both particles are engaged.

There is recombination band band via traps which is a nonradioactive recombination. It can be proportional to either p or n or np. It can be first order or second order or mono molecular or biomolecular.

Auger recombination where the rate r is proportional to nnp or ppn which is third order.

All these re combinations can be considered nongeminate recombination as only the free electrons and holes are considered involved.

Geminate recombination occurs when weakly bound electron hole pairs recombine with each other.

More about geminate and nongeminate recombination in the link:https://www.researchgate.net/post/What_is_the_meaning_of_geminate_and_non-geminate_recombination_in_solar_cells#view=5b8ba5d7979fdc70122d7441

Best wishes