Question

Explain the process of formation of 'depletion layer' and 'potential barrier' in a p-n junction region of a diode, with the help of a suitable diagram. Which feature of junction diode makes it suitable for its use as a rectifier?

Hint:

For p-n junction problems: - The depletion layer forms due to carrier recombination near the junction. - The diode’s rectifying property arises from its ability to conduct in only one direction.

Answer 1

Step 1: Formation of the depletion layer.
A p-n junction is formed by joining p-type (excess holes) and n-type (excess electrons) semiconductors. Due to the concentration gradient, electrons from the n-side diffuse to the p-side, and holes from the p-side diffuse to the n-side. These carriers recombine near the junction, leaving a region devoid of free charges called the depletion layer. The p-side near the junction becomes negatively charged (due to acceptor ions), and the n-side becomes positively charged (due to donor ions). Step 2: Formation of the potential barrier.
The charge separation in the depletion layer creates an electric field from the n-side (positive) to the p-side (negative). This field opposes further diffusion of majority carriers, forming a potential barrier. At equilibrium, this barrier prevents further net movement of charges, with a typical value of 0.7 V for silicon diodes. Step 3: Diagram description.
The diagram shows a p-n junction with the p-side on the left and n-side on the right. The depletion layer is a shaded region around the junction, with negative ions on the p-side and positive ions on the n-side. An arrow indicates the electric field from n to p, and a potential energy graph shows the barrier height. Step 4: Feature for rectification.
The junction diode’s unidirectional current flow makes it suitable as a rectifier: it conducts in forward bias (p to n) but blocks current in reverse bias (n to p), enabling AC to DC conversion.