What is "saturation current"

n. (context physics English) the maximum current that can be obtained in a specific circuit under specified conditions

The saturation current (or scale current), more accurately, the reverse saturation current, is that part of the reverse current in a semiconductor 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, the reverse bias saturation current for an ideal p–n diode, is given by (Schubert 2006, 61):

$I_\mathrm{S} = e A \left( \sqrt{\frac{D_\mathrm{p}}{\tau_\mathrm{p}}} \frac{n_\mathrm{i}^2}{N_\mathrm{D}} + \sqrt{\frac{D_\mathrm{n}}{\tau_\mathrm{n}}} \frac{n_\mathrm{i}^2}{N_\mathrm{A}} \right),\,$

where

e is elementary charge A is the cross-sectional area D are the diffusion coefficients of holes and electrons, respectively, N are the donor and acceptor concentrations at the n side and p side, respectively, n is the intrinsic carrier concentration in the semiconductor material, τ are the carrier lifetimes of holes and electrons, respectively.

Note that the saturation current is not a constant for a given device; it varies with temperature; this variance is the dominant term in the temperature coefficient for a diode. A common rule of thumb is that it doubles for every 10°C rise in temperature. (Bogart 1986, 40)