What is saturation current and for which purpose it is taken.........?

what is saturation current and for which purpose it is taken…???

Saturation current is a term used in relation to semiconductor diodes. It is more fully named reverse saturation current and is "part of the reverse current in a diode caused by diffusion of minority carriers from the neutral regions to the depletion region.
I S, the reverse bias saturation current for an ideal p-n diode is given by,
image
where
I S is the reverse bias saturation current,
e is elementary charge
A is the cross-sectional area
D p,n are the diffusion coefficients of holes and electrons, respectively,
N D,A are the donor and acceptor concentrations at the n side and p side, respectively,
ni is the intrinsic carrier concentration in the semiconductor material,
τp,n are the carrier lifetimes of holes and electrons, respectively.