Saturation current is a term used in relation to semiconductor

Semiconductor

A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...

 diode

Diode

In electronics, a diode is a type of two-terminal electronic component with a nonlinear current–voltage characteristic. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material connected to two electrical terminals...

s. It is more fully, and accurately, 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. This current is almost independent of the reverse voltage." (Steadman 1993, 459)

I_S, the reverse bias saturation current for an ideal p-n diode

Diode

In electronics, a diode is a type of two-terminal electronic component with a nonlinear current–voltage characteristic. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material connected to two electrical terminals...

 is given by, (Schubert 2006, 61)



where

I_S is the reverse bias saturation current,

e is elementary charge

Elementary charge

The elementary charge, usually denoted as e, is the electric charge carried by a single proton, or equivalently, the absolute value of the electric charge carried by a single electron. This elementary charge is a fundamental physical constant. To avoid confusion over its sign, e is sometimes called...

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,

n_i is the intrinsic carrier concentration in the semiconductor material, are the carrier lifetimes of holes and electrons, respectively.