Physics 2015 JAMB Past Questions - Question 13: The current in a reverse-biased junction is due to

Correct Answer

B

Explanation

In a reverse-biased semiconductor junction, the current is primarily due to minority charge carriers (either minority electrons or minority holes) that are thermally generated and diffuse across the junction. Let me explain this in more detail:

1. Reverse Bias: In a semiconductor diode, reverse bias means that the voltage is applied in a way that the p-type region is connected to the negative terminal of the voltage source, and the n-type region is connected to the positive terminal. This arrangement creates a strong electric field that opposes the flow of majority charge carriers (electrons in the n-region and holes in the p-region) across the junction. As a result, a very small current, called the reverse current or reverse saturation current, flows in the reverse direction.

2. Minority Carriers: In a semiconductor, there are both majority and minority charge carriers. Majority carriers are the dominant carriers in a region (electrons in the n-region, holes in the p-region), and minority carriers are the less abundant carriers in that region.

3. Generation and Diffusion: Even in the absence of an applied voltage, some minority carriers are thermally generated in the depletion region near the junction. These minority carriers are generated through processes like thermal excitation. Once generated, they can diffuse and move across the depletion region due to the electric field.

4. Current Flow: As these minority carriers diffuse and move across the depletion region, they contribute to the reverse current. This current is relatively small compared to the forward bias current, but it is non-zero because of the thermal generation of minority carriers and their subsequent diffusion.

In summary, the current in a reverse-biased junction is primarily due to the thermally generated minority charge carriers (minority electrons or minority holes) diffusing across the junction under the influence of the electric field. It's important to note that this reverse current is typically much smaller than the forward bias current in a diode under normal operating conditions.