Question

On increasing reverse voltage in a p-n junction diode, the value of reverse current will
(A) Gradually increase
(B) First remain constant and then suddenly increase
(C) Remain constant
(D) Gradually decrease

Answer 1

Hint: When a reverse voltage is applied across a diode, a reverse current flows, which is because of the minority charge carriers. The minority carriers are driven under the force applied by the electric field across the depletion region.

Complete step-by-step solution
A p-n junction can be biased in two different manners; forward bias and reverse bias. When the p side of the diode is connected to the positive terminal of the battery, and the n side of the diode is connected to the negative terminal of the battery, then the p-n junction diode is said to be forward biased. But if the p and n sides of the diode are connected in the opposite manner to the terminals of the battery then the diode is said to be reversed biased.
Now, we know that the width of the depletion region is more in the case if the reverse biasing. According to the question, the p-n junction is reverse biased so the width of the depletion region must be more. Because of this depletion region, the flow of the electrons from the n side to the p side, and the flow of the holes from the p side to the n side, is restricted. So the current through the diode will only be because of the minority carriers. So this current is called the reverse current.
Now, since the minority charge carriers are present in a very small concentration within the diode, so even a small voltage is sufficient to sweep them from one side of the junction to the other side. Therefore the reverse current is independent of the magnitude of the reverse voltage applied.
But when the reverse voltage is increased beyond the breakdown voltage limit, the electric field across the junction becomes sufficient to pull out the valence electrons from the atoms at the p side and sweep them to the n side. Due to this, the reverse current suddenly increases.
Thus, the reverse current first remains constant, then suddenly increases on increasing the reverse voltage.
Hence, the correct answer is option B.

Note
The property of the sudden increase of the reverse current on increasing the reverse voltage is used to make many useful devices. For example the Zener diode, which is used for regulating the voltage in a circuit, is operated under reverse bias.