Saturation current is a term used in electronics and refers to the part of the reverse current in a semiconductor diode caused by the diffusion of minority carriers from the neutral regions to the depletion region. The reverse bias saturation current for an ideal p-n diode is given by the following equation:

I0 = qA(DpNn + DnNp) / W

where:

• q is the elementary charge
• A is the cross-sectional area
• Dp and Dn are the diffusion coefficients of holes and electrons, respectively
• Nn and Np are the donor and acceptor concentrations at the n side and p side, respectively
• ni is the intrinsic carrier concentration in the semiconductor material
• W is the depletion region width

The saturation current is almost independent of the reverse voltage and is not a constant for a given device; it varies with temperature, doubling for every 10 °C rise in temperature. Saturation current is also a term used in the photoelectric effect, where it refers to the maximum current that can be produced by a photoelectric cell when the intensity of the incident light is increased beyond a certain level.