Question

When p-n junction is reverse biased (A) no current flows (B) majority carriers move towards the junction (C) minority carriers move towards the junction (D) both majority and minority carriers move away from the junction

Short answer

In a reverse biased p-n junction, the minority carriers (electrons in the p-side and holes in the n-side) move towards the junction. So, the correct answer is (C) minority carriers move towards the junction.

Step-by-step solution

Understanding p-n junction

A p-n junction is formed when a p-type semiconducting material, which has majority carriers as holes, is joined with an n-type semiconducting material, which has majority carriers as electrons.

Reverse bias

A p-n junction is said to be reverse biased when the voltage is applied in such a way that the potential barrier at the junction increases. In this case, the positive terminal of the battery is connected to the n-type material, and the negative terminal is connected to the p-type material.

Majority and minority carriers

Majority carriers are the dominant charge carriers in a semiconducting material. In a p-type material, holes are the majority carriers, while in an n-type material, electrons are the majority carriers. Minority carriers are the less-dominant charge carriers in a semiconducting material. Electrons are minority carriers in p-type material, and holes are minority carriers in n-type material.

Carrier movement in reverse biased p-n junction

When a p-n junction is reverse biased, the potential barrier increases. This effectively discourages majority carriers (holes in the p-side and electrons in the n-side) from moving across the junction. So, they move away from the junction. On the other hand, the minority carriers (electrons in the p-side and holes in the n-side) get attracted to the respective battery terminals, and thus they move towards the junction. Based on the analysis, the correct answer is: (C) minority carriers move towards the junction

Key concepts

reverse bias

When a p-n junction is subjected to reverse bias, the applied voltage encourages the movement of charge carriers in a specific direction. In this setup, the positive terminal of the external battery is connected to the n-type side, and the negative terminal is connected to the p-type side.
This configuration increases the potential barrier, making it even more challenging for charge carriers to traverse the junction. As a result, the majority carriers refrain from moving towards the junction, effectively halting their contribution to current flow. This scenario is vital for the operation of various electronic components like diodes and is a fundamental concept in understanding semiconductor electronics.

majority carriers

Majority carriers in semiconducting materials are the charge carriers that exist in greater numbers and significantly impact the electrical characteristics of the material. In p-type semiconductors, holes are the predominant carriers. Conversely, in n-type semiconductors, electrons take on the role of majority carriers.
The behavior of majority carriers is critical when a p-n junction is in forward or reverse bias. In reverse bias, majority carriers are pushed away from the junction due to the increased potential barrier. This movement reduces the likelihood of current flow across the junction, highlighting the essential role of majority carriers in determining the conductivity of semiconductors.

minority carriers

Minority carriers are the less common charge carriers in semiconducting materials. Their behavior becomes especially important when a p-n junction is in reverse bias. In a p-type material, electrons are the minority carriers, and in an n-type material, holes are the minority carriers.
Unlike majority carriers, in reverse bias, minority carriers are influenced by the increased electric field. They are attracted towards the junction, where they actually contribute to the current, albeit a very small one known as reverse saturation current. Understanding the subtle effects of minority carriers helps in appreciating their influence on the characteristics of devices like photodetectors and solar cells.

semiconducting materials

Semiconducting materials are pivotal in modern electronics, thanks to their intermediate electrical conductivity that can be precisely controlled. Intrinsic semiconductors are pure forms, typically made of silicon or germanium, where the number of electrons and holes are nearly equal.
By introducing impurities through a process called doping, you can increase the number of electrons or holes, creating n-type or p-type semiconductors, respectively. This controlled manipulation of charge carriers allows for the innovation of devices like transistors, diodes, and various sensors. Semiconducting materials serve as the backbone of the electronic components that power our daily tech gadgets, demonstrating their unmatched versatility in engineering.