Question: Formation of Depletion Layer and Potential Barrier in a p-n Junction

Step 1: Formation of Depletion Layer and Potential Barrier [1.5 Marks]

• When a p-n junction is formed, the difference in concentration of charge carriers in the two regions causes diffusion of holes from the p-side to the n-side and electrons from the n-side to the p-side.
• As electrons diffuse from n to p, they leave behind ionized donor atoms ($N_D^+$) in the n-region. Similarly, as holes diffuse from p to n, they leave behind ionized acceptor atoms ($N_A^-$) in the p-region.
• This creates a region devoid of mobile charge carriers near the junction, known as the depletion layer.
• The accumulation of these immobile ions creates an electric field ($E$) directed from the n-side to the p-side, which opposes further diffusion. This creates a potential difference across the junction, known as the potential barrier ($V_B$).

Step 2: Diagrammatic Representation [0.5 Mark]

Step 3: Feature for Rectification [1.0 Mark]

• The feature that makes a junction diode suitable for rectification is its unidirectional conduction property.
• A p-n junction diode offers low resistance when forward biased (p-side at higher potential) and very high resistance when reverse biased (p-side at lower potential).
• This allows current to flow only in one direction, effectively converting alternating current (AC) into direct current (DC).