3-5. Reverse recovery time

When diodes and other semiconductor devices are on, current flows because of free electrons and holes (carriers). In addition, these carriers are accumulated as electric charge in the depletion region formed across a junction or in a parasitic capacitor and also accumulated in the lightly doped region as excess carriers. (This causes the above-mentioned conductivity modulation.) When these devices transition from the on state to the off state, they release electrons just like a capacitor. The resulting flow of electrons is observed as a current flow in the opposite direction.
The forward voltage (V_F) is positive while the current (i_F) is between zero and the peak reverse recovery current (I_rr). During this period, the electric charge in the depletion region and the parasitic capacitor is mainly released, causing negative current to flow. Once iF reaches Irr, the excessive carriers (electrons and holes) that contributed to the conductivity modulation disappear because they recombine. Therefore, the time required for this recombination depends on the carrier lifetime.