As discussed elsewhere, there are various recombination mechanisms within even a uniformly doped piece of semiconductor. In the bulk of the material the carriers recombine by either radiative (also known as band-to-band) recombination, Auger recombination or Shockley-Read-Hall (SRH) via traps within the energy gap.
The lifetime of carriers in the material bulk τb is composed of radiative lifetime τrad, Auger lifetime τA and a SRH lifetime τSRH with the relation:
For an indirect bandgap semiconductor such as silicon τrad is very large and usually neglected.
The auger lifetime time can be calculated using theoretical models , however, the SRH lifetime depends on the level of defects in the crystal lattice and so is difficult to calculate theoretically. The bulk lifetime for extrinsic silicon can be determined using semi-empirical models based on lifetime measurements of float-zone silicon with very low defect levels. The lifetime is dependent on the excess carriers and doped atoms concentrations. The models presented here are based on  but more recent model was developed. Most silicon wafers have higher levels of contaminants and so lower lifetimes than calculated here. Further details on silicon properties are in the appendices.
Bulk Lifetime for p-type Silicon
Bulk Lifetime for n-type Silicon
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