Question

Reverse bias applied on a junction diode: (A) raises the potential barrier (B) increases majority charge carrier current (C) lowers the potential barrier (D) increases the temperature of junction

Short answer

Applying reverse bias on a junction diode (A) raises the potential barrier, preventing majority charge carriers from crossing the junction.

Step-by-step solution

Understanding Junction Diodes

A junction diode is a two-terminal electronic device made of semiconductor material. It typically consists of a P-type semiconductor (with majority carriers being holes) and an N-type semiconductor (with majority carriers being electrons). When these materials are brought into contact, a junction is formed, known as the P-N junction. The P-N junction has a potential barrier (also known as a depletion region) due to the migration of majority carriers from their respective sides to the other side, leaving behind charged ions.

Biasing of Junction Diodes

There are two types of biasing in junction diodes: forward bias and reverse bias. Forward bias occurs when the P-type material is connected to the positive terminal and the N-type material is connected to the negative terminal of an external voltage source. In this case, the applied potential difference reduces the potential barrier of the junction, allowing majority charge carriers to flow across the junction. Reverse bias, on the other hand, is when the P-type material is connected to the negative terminal and the N-type material is connected to the positive terminal of the external voltage source. In this case, the potential difference increases the potential barrier and prevents majority charge carriers from crossing the junction. As a result, the current flow in the diode is minimal in reverse bias.

Analyzing the Effects of Reverse Bias

Now, let's analyze the given options based on the understanding of the working of a junction diode under reverse bias: (A) raises the potential barrier: As discussed earlier, applying reverse bias increases the potential barrier, preventing majority charge carriers from crossing the junction. So, this statement is correct. (B) increases majority charge carrier current: In reverse bias, the potential barrier prevents the majority charge carriers from crossing the junction, which essentially means the majority charge carrier current decreases. Thus, this statement is incorrect. (C) lowers the potential barrier: This statement is the opposite of what occurs under reverse bias, which increases the potential barrier. Therefore, this statement is incorrect. (D) increases the temperature of junction: The temperature of the junction is not directly related to the reverse bias applied to the diode. It may increase due to the power dissipation in the diode, but it is not a direct effect of reverse bias itself. So, this statement is also incorrect. Based on the analysis, option (A) is the correct answer.

Key concepts

Junction Diode

A junction diode is an essential component in modern electronics. Operated as a two-terminal device, it is crafted using semiconductor materials.
The two main types are P-type and N-type semiconductors.

• P-type semiconductor: Predominantly has holes as the majority charge carriers.
• N-type semiconductor: Mainly contains electrons as the majority charge carriers.

When these two semiconductor types are joined, they form what is known as a P-N junction.
A crucial aspect of this junction is the formation of a potential barrier, which regulates current flow across the junction. Upon junction formation, charge carriers migrate, creating a depletion region—this is the barrier preventing the recombination of electrons and holes.
Understanding the behavior of these charge carriers under different conditions, like forward and reverse bias, offers insights into the functionality of electronic circuits.

Semiconductors

Semiconductors are fundamental materials used in electronic components. Unlike conductors, which allow free movement of electrons, semiconductors have a more controlled electron movement. This is due to their unique band structure, which allows them to conduct electricity under certain conditions.
There are mainly two types:

• P-type Semiconductors: These are formed by doping pure semiconductors with elements that create 'holes' or an absence of electrons. Holes act as positive charge carriers.
• N-type Semiconductors: Created by adding elements with additional electrons that become free to move, acting as negative charge carriers.

Semiconductors can switch between being insulators and conductors when influenced by factors like temperature, doping, and applied voltage.
This unique ability makes them indispensable in creating devices like diodes, transistors, and other components which rely on precise control of electron movement.

Potential Barrier

The potential barrier in a junction diode is a key concept in its operation. Formed at the P-N junction, this barrier is a result of the migration of charge carriers. Electrons and holes move and combine across the junction, leaving behind charged ions.
This process leads to the formation of the depletion region, a zone devoid of free charge carriers. The potential barrier acts as a restraining wall for charge carriers:

• In forward bias, the applied voltage lowers this barrier, allowing charge carriers to cross and conduct current.
• In reverse bias, the barrier heightens, impeding the flow of majority charge carriers and drastically reducing the current.

Thus, the potential barrier is pivotal in controlling the current flow direction and magnitude in a diode, dictating its functionality in electrical circuits.

Majority Charge Carriers

Majority charge carriers are the predominant type of charge found in semiconductors
In P-type semiconductors, this means holes, while in N-type semiconductors, these are electrons.

• In forward bias: The majority charge carriers cross the potential barrier more easily, allowing significant current flow.
• In reverse bias: The potential barrier increases, making it difficult for the majority charge carriers to cross, thus reducing the current flow.

An understanding of how these carriers behave under various biasing scenarios helps in predicting the diode's performance. Control of these carriers is critical for the diode's application in the rectification, switching, and signal modulation in electronic devices. Through proper biasing, we can manipulate these carriers to achieve the desired electronic outcomes.