Question

The avalanche breakdown in p-n junction is due to
$(a)$ Shift of Fermi level
$(b)$ Cumulative effect of conduction band electron
$(c)$ Widening of forbidden gap
$(d)$ High impurity concentration

Answer 1

Hint – In this question use the concept that avalanche breakdown occurs in the reverse breakdown region, when a high reverse voltage is applied across the diodes. Think of the consequences that can happen when such high potential is applied in the reverse region. This will help getting the right option for this problem statement.

Complete Step-by-Step solution:
Avalanche breakdown occurs in a p-n junction diode when it is moderately doped and has a thick junction (i.e. its depletion layer width is high).
Avalanche breakdown usually occurs when we apply a reverse voltage across the diode higher than the Zener breakdown voltage.
So in reverse bias, due to applied electric field, electrons acquire enough energy to free more electrons bound to the atom so that the abundant number of electron-hole pairs are created for conduction, this is called the cumulative effect of conduction band electron.
So this is the required answer.
Hence option (B) is the correct answer.

Note – There is another important breakdown that occurs when a diode is operated in reverse region. That is the zener breakdown, however it is different from avalanche breakdown. Avalanche breakdown occurs because of the ionization of electron and hole pairs whereas the Zener breakdown occurs because of heavy doping.