Question

In Figure, Vo is the potential barrier across a p-n junction, when no battery is connected across the junction ______.

Options

• 1 and 3 both correspond to forward bias of junction.

• 3 corresponds to forward bias of junction and 1 corresponds to reverse bias of junction.

• 1 corresponds to forward bias and 3 corresponds to reverse bias of junction.

• 3 and 1 both correspond to reverse bias of junction.

Answer 1

In Figure, Vo is the potential barrier across a p-n junction, when no battery is connected across the junction 3 corresponds to forward bias of junction and 1 corresponds to reverse bias of junction.

Explanation:

P-N Junction Diode: When a P-type semiconductor is suitably joined to an N-type semiconductor, then the resulting arrangement is called a P-N junction or P-N junction diode.

(1) Depletion region: On account of the difference in concentration of charge carrier in the two sections of the P-N junction, the electrons from N-region diffuse through the junction into P-region and the hole from the P region diffuses into N-region.

Due to diffusion, the neutrality of both N and P-type semiconductor is disturbed and a layer of negatively charged ions appear near the junction in the P-crystal and a layer of positive ions appears near the junction in N-crystal. This layer is called the depletion layer.

1. The thickness of the depletion layer is 1 micron = 10–6 m.
2. Width of the depletion layer ∝ `1/"Dopping"`
3. Depletion is directly proportional to temperature.
4. The P-N junction diode is equivalent to the capacitor in which the depletion layer acts as a dielectric.

(2) Potential barrier: The potential difference created across the P-N junction due to the diffusion of electrons and holes is called the potential barrier.

For Ge, V_B = 0.3 V and for silicon V_B = 0. 7 V

On average the potential barrier in a P-N junction is – 0.5 V and the width of the depletion region = 10^–6m.

So the barrier electric field `E = V/d = 0.5/10^-6 = 5 xx 10^5` V/m

The height of the potential barrier is decreased when the p-n junction is forward biased, it opposes the potential barrier junction when the p-n junction is reverse biased and it supports the potential barrier junction, resulting increase in the potential barrier across the junction.