When is the p-n junction called reverse bias and explain the change in p-n junction from this type of connection.

Explanation

When and external voltage (V) is applied across the diode such that n-side is positive and p-side is negative it is said to be reverse biased. This is shown in figure.

Diagram (b) for the circuit is as follows :

The applied voltage mostly drops across the depletion region according to figure (a).
The direction of applied voltage `V_(0)` is same as the direction of barrier potential V. As a result, the barrier height increases and the depletion region widens due to the change in the electric field.

The effective barrier height under reverse bias is `V+V_(0)`.
In figure (c ), the battery is not connected to p-n junction, potential barrier `V_(0)` is shown as 1 and when voltage of the external battery is applied, its effective potential barrier `V_(0)+V` is shown as 2.
This suppresses the flow of electrons from `n to p` and holes from `p to n` due to effective depletion barrier potential means current are disputed due to majority charge carriers hence diffusion current is not obtained.
Although some minority charge carriers pass through the junction due to the high voltage applied by external battery hole in n-region and electron in p-region and current flow in reverse direction is called reverse current. However, for large reverse voltage, the increase in reverse current shows less.
Reverse current does nto depend only on the applied voltage. The current is not limited by the magnitude of the applied voltage but is limited due to the concentration of the minority carrier on either side of junction.
Some voltage is also sufficient to across the junction for minority carriers.
The reverse bias voltage varies from about 10 V to 15 V.
Here current obtained in the order of microampere `(muA)`.