Question

Which of the following is/are true regarding breakdown voltage of Zener diode?

• A. If the reverse bias voltage across a p-n junction diode is increased, at a particular voltage the reverse current suddenly decreases to a large value
• B. The holes in the n-side and the conduction electrons in the p-side are accelerated due to the reverse bias voltage.
• C. The voltage at which the rate of creation of hole-electron pairs is increased leading to the increased current is called avalanche breakdown
• D. None of the above

Answer 1

Answer: (B)

The holes in the n-side and the conduction electrons in the p-side are accelerated due to the reverse bias voltage.

Consider applying an external voltage to the junction with the the negative terminal connected to the P type material and the positive terminal connected to the N type material. For the P-N junction this would require injecting electrons into the P type material. These electrons would recombine with holes and therefore further deplete the majority charge carriers in the P type semiconductor.

Also removing electrons from the N type material would obviously cause further depletion the free electrons (the majority charge carriers in the N type semiconductor). This causes a widening of the depletion layer and an increase in the charge at the junction which reinforces the barrier voltage to oppose the applied voltage. The net result is that when the P-N junction is reversed biased it blocks current flow.