Saturation current
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): where Increase in reverse bias does not allow the majority charge carriers to diffuse across the junction. However, this potential helps some minority charge carriers in crossing the junction. Since the  minority charge carriers in the n-region and p-region are produced by thermally generated electron-hole pairs, these minority charge carriers are extremely temperature dependent and independent of the applied bias voltage. The applied bias voltage acts as a forward bias voltage for these minority charge carriers and a current of small magnitude flows in the external circuit in the direction opposite to that of the conventional current due to the moment of majority charge carriers. 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)