Explain V-I Characteristics of P-N junction.

Forward biasing:

A p-n junction is said to be forward biased, if the positive terminal of the external battery B is connected to p-side and the negative terminal to the n-side of the p-n junction. 

Here the forward bias opposes the potential barrier VB and so the depletion layer becomes thin. The majority charge carriers in the P type and N types are repelled by their respective terminals due to battery B and hence cross the junction. On crossing the junction, recombination process takes place. For every electron hole combination, a covalent bond near the +ve terminal of the battery B is broken and this liberates an electron which enters the +ve terminal of B through connecting wires. 

This in turn creates more holes in P-region. At the other end, the electrons from -ve terminal of B enter n-region to replace electron lost due to recombination process. Thus a large current will flow to migration of majority carriers across the p-n junction which is called forward current.

Reverse biasing: 

A p-n junction is said to be reverse biased if the positive terminal of the battery B is connected to N-side and the negative terminal to p-side of the p-n junction. The majority carriers are pulled away from the junction and the depletion region becomes thick. The resistance becomes high when reverse biased and so there is no conduction across the junction due to majority carriers. The minority carriers however cross the junction and they constitute a current that flows in the opposite direction. This is the reverse current.

The V-I characteristics of a p-n junction diode: