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Chapter 20: Problem 18

When forward bias is applied to a \(P-N\) junction, then what happens to the potential barrier \(V_{B}\), and the width of charge depleted region \(x\) (A) \(V_{B}\) increases, \(x\) decreases (B) \(V_{B}\) decreases, \(x\) increases (C) \(V_{B}\) increases, \(x\) increases (D) \(V_{B}\) decreases, \(x\) decreases

Short Answer

Expert verified
When a forward bias is applied to a P-N junction, the potential barrier \(V_{B}\) decreases and the width of the charge depleted region \(x\) also decreases. Therefore, the correct answer is (D) \(V_{B}\) decreases, \(x\) decreases.

Step by step solution

01

Observe the effect of forward bias on P-N junction

When forward bias is applied to a P-N junction, it means that the positive terminal of the voltage source is connected to the p-type semiconductor, and the negative terminal is connected to the n-type semiconductor. As a result, the external voltage works against the potential barrier, reducing its height.
02

Evaluate the potential barrier (V_B)

The forward bias voltage works to lower the potential barrier by the amount of the applied voltage. Thus, the potential barrier (V_B) will decrease when a forward bias is applied to the P-N junction.
03

Evaluate the width of the charge depleted region (x)

As the potential barrier is reduced due to the forward bias, the electric field in the depletion region decreases. Consequently, the width of the charge depleted region (x) also decreases.
04

Choose the correct option

From our analysis, we have determined that the potential barrier (V_B) decreases and the width of the charge depleted region (x) decreases when a forward bias is applied to the P-N junction. Therefore, the correct answer is: (D) V_B decreases, x decreases

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Forward Bias
When a PN junction diode is forward-biased, it means the external voltage is applied in such a way that the positive terminal is connected to the p-type material and the negative terminal to the n-type material. This configuration facilitates the flow of charge carriers across the junction.
This is because the external voltage effectively pushes against the built-in potential of the diode, allowing current to flow more easily. Here's a breakdown of the process:
  • The forward-bias voltage reduces the barrier that naturally exists between the two sides of the junction.
  • Carriers like electrons and holes gain enough energy to overcome the potential barrier.
  • This allows more carriers to flow across the junction, which results in an increase in the current.
For students, understanding forward bias is crucial as it is the basis of diode operation in conductive states, impacting how devices like LEDs and power rectifiers function.
Potential Barrier
A potential barrier is a critical concept when discussing PN junctions. It represents the energy barrier that must be overcome for charge carriers to move across the junction between n-type and p-type materials.
In the context of forward bias, the potential barrier decreases. Here's why:
  • The positive external voltage neutralizes some of the built-in electric field created by the initial charge distribution at the junction.
  • As this electric field diminishes, the energy barrier naturally in the junction becomes lower.
  • This reduction facilitates a greater flow of charge, enhancing current through the diode.
Understanding the potential barrier is essential for grasping how current flows in a semiconductor device when it's operational, and how resistance is offered under various conditions.
Depletion Region
The depletion region in a PN junction is an area where mobile charge carriers are absent, formed due to the initial recombination of holes and electrons when the junction is created.
In a forward-biased situation, the characteristics of this region change significantly:
  • As the forward bias reduces the potential barrier, the electric field in this region also diminishes.
  • The depletion region width decreases, which means fewer areas for electron-hole recombination prepare themselves for reduced resistance to carrier movement.
  • This reduction accelerates the current flow, versus an unbiased junction which restricts movement.
The depletion region's dynamics under forward bias underpin the operational capacity of diodes, particularly in circuits requiring efficient current regulation.

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Most popular questions from this chapter

Carbon, silicon and germanium have four valence elements each. At room temperature which one of the following statement(s) is most appropriate? [2007] (A) The number of free electrons for conduction is significant in all the three (B) The number of free electrons for conduction is significant only in Si and Ge but small in \(C\) (C) The number of free conduction electrons is significant in \(C\) but small in \(\mathrm{Si}\) and \(\mathrm{Ge}\) (D) The number of free conduction electrons is negligibly small in all the three

If a full wave rectifier circuit is operating from \(50 \mathrm{~Hz}\) mains, the fundamental frequency in the ripple will be (A) \(50 \mathrm{~Hz}\) (B) \(70.7 \mathrm{~Hz}\) (C) \(100 \mathrm{~Hz}\) (D) \(25 \mathrm{~Hz}\)

Read the following questions and choose (A) If both Assertion and Reason are true and Reason is the correct explanation of the Assertion. (B) If both Assertion and reason are true but Reason is not correct explanation of the Assertion. (C) If Assertion is true but Reason is false. (D) If Assertion is false but Reason is true. Assertion: The conductivity of intrinsic semiconductors at \(0 \mathrm{~K}\) is zero. Reason: At \(0 \mathrm{~K}\) no energy is available. No covalent bond can be broken. No free electron is available for conduction. (A) \(\mathrm{A}\) (B) \(\mathrm{B}\) (C) \(\mathrm{C}\) (D) D

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