Using the necessary circuit diagram, show how the V-I characteristics of a p-n junction are obtained in (i) forward biasing (ii) Reverse biasing. How are these characteristics made use of in rectification?

Explanation

(a) (i) p-n junction diode under forward bias:
The V-I characteristics of p-n junction in forward bias is shown below:
p-side is connected to the positive terminal and n-side to the negative terminal.
Applied voltage drops across the depletion region.
Electron in n-region moves towards the p-n junction and holes in the p-region move towards the junction. The width of the depletion layer decreases and hence, it offers less resistance.
Diffusion of majority carriers takes place across the junction. This leads to the forward current.


(ii) p-n junction under reverse bias :
Positive terminal of battery is connected to n-side and negative terminal to p-side
Reverse bias supports the potential barrier. Therefore, the barrier height increases and the width of depletion region also increases.
Due to the majority carriers, there is no conduction across the junction. A few minority carriers cross the junction after being accelerated by high reverse bias voltage.

This constitutes a current flows in opposite direction, which is called reverse current.
The V-I characteristics of p-n junction diode in reverse bias is shown on previous page.
p-n junction diode is used as a half-wave rectifier. Its working is based on the fact that the resistance of p-n junction becomes low when forward biased an becomes high when reverse biased. These characteristics of diode is used in rectification.