In a PN junction diode, the inverse saturation current is due to the diffusive flux of the minorities electrons from the p-part to the n-part and the minor holes from the side N to the lateral side P.
There are two common sources of reverse voltage:
(1) when the power is disconnected from a system.
(2) when the FET body diode becomes biased in front.
When the diode is reversed, the width of the depletion area increases, most vectors are removed from the junction, and there is no current current due to the majority vectors, but there are also pairs of thermally produced electrons.
If these electrons and these holes are generated near the junction, then there is a current flow. The negative voltage applied to the diode tends to attract the holes thus generated and to reject the electrons.
At the same time, the positive voltage will draw the electrons to the battery and will reject the holes.
This will cause the current to flow into the circuit. This current is usually very small (micro-to-nano amps).
Because this current is due to minority carriers and this number of minority carriers is set to a certain temperature, the current is almost constantly known as the ICO reverse saturation current.