Question
Download Solution PDFWhat happens to the depletion layer in a P-N junction when it is reverse-biased?
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFExplanation:
Behavior of the Depletion Layer in a P-N Junction Under Reverse Bias
Definition: The depletion layer in a P-N junction refers to the region near the junction where mobile charge carriers (holes and electrons) are depleted, leaving behind immobile charged ions. This region forms as a result of the diffusion of charge carriers across the junction, leading to the creation of an electric field that opposes further diffusion.
Reverse Biasing: When a P-N junction is reverse-biased, the positive terminal of the external voltage source is connected to the N-type material, and the negative terminal is connected to the P-type material. This configuration increases the potential barrier across the junction, making it harder for charge carriers to cross the junction.
Correct Option Analysis:
The correct option is:
Option 4: The depletion layer widens.
When a P-N junction is reverse-biased, the external voltage increases the potential difference across the junction. This additional voltage reinforces the electric field within the depletion region, causing the depletion layer to widen. As the width of the depletion layer increases, more immobile ions are uncovered due to the drifting away of mobile charge carriers. This widening leads to a higher resistance across the junction, effectively blocking current flow except for a very small leakage current caused by minority carriers.
Explanation:
- Under reverse bias, the majority carriers (electrons in the N-region and holes in the P-region) are pushed away from the junction. This results in an increase in the number of uncovered immobile charged ions, causing the depletion region to expand.
- The widening of the depletion layer increases the electric field intensity, which further inhibits the movement of charge carriers across the junction.
- Current flow under reverse bias is minimal and is primarily due to the movement of minority carriers, which are unaffected by the widening of the depletion layer.
- This property of reverse biasing is utilized in applications such as diodes used for rectification, Zener diodes for voltage regulation, and photodiodes.
Applications:
- Rectification: Reverse-biased P-N junctions are used in diodes to block current flow in one direction, allowing only unidirectional current flow.
- Voltage Regulation: Zener diodes exploit reverse bias characteristics to maintain a constant voltage across circuits.
- Detection of Light: Photodiodes use reverse-biased P-N junctions to convert light energy into electrical energy.
Important Information
To further understand the analysis, let’s evaluate the other options:
Option 1: The depletion layer disappears.
This option is incorrect because the depletion layer does not disappear under reverse bias. On the contrary, the depletion layer widens as the external voltage reinforces the electric field within the junction, pushing majority carriers further away from the junction.
Option 2: The depletion layer narrows.
This option is incorrect as it describes the behavior of the depletion layer under forward bias, not reverse bias. When the P-N junction is forward-biased, the external voltage reduces the potential barrier, allowing more charge carriers to recombine near the junction and effectively narrowing the depletion region.
Option 3: The depletion layer remains unchanged.
This option is also incorrect because the external reverse bias voltage actively influences the junction, increasing the width of the depletion layer. The depletion layer cannot remain unchanged under reverse bias conditions.
Conclusion:
Under reverse bias, the depletion layer in a P-N junction widens due to the increased external voltage, which enhances the electric field within the junction. This widening inhibits the flow of majority carriers, resulting in minimal current flow across the junction. Understanding the behavior of the depletion region under different biasing conditions is crucial for analyzing the functionality of semiconductor devices, such as diodes and transistors, in electronic circuits.
Last updated on Jul 2, 2025
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