Forward And Reverse Bias

NCERT explains that under reverse bias the external voltage adds to the internal barrier, widening the depletion region and preventing majority carriers from crossing. However, thermally generated minority carriers, electrons in the p-side and holes in the n-side, are swept across the junction by the strong field, producing a very small reverse current called the reverse saturation current. This current is nearly independent of the applied voltage because it is limited by the rate of thermal generation of minority carriers, not by the voltage. The option about majority carriers tunnelling is wrong because ordinary reverse current below breakdown is a minority-carrier drift effect, not tunnelling. The option that the barrier vanishes is wrong because reverse bias increases, not removes, the barrier. The option that no current flows at all is wrong because a small measurable saturation current always exists due to thermal generation. As stated in NCERT Class 12, Chapter 14, reverse current arises from minority carriers and quickly saturates because essentially every minority carrier generated near the junction is collected. A consistency check confirms it grows sharply with temperature, since more heat generates more minority carriers, which is exactly why reverse saturation current is a strong indicator of the operating temperature of a diode.