Question

To get an 'n' type doped semiconductor, impurity to be added to silicon should have the following number of valence electrons: (a) 1 (b) 2 (c) 3 (d) 5

Short answer

The impurity should have 5 valence electrons (option d).

Step-by-step solution

Understand the Concept of Doping

In semiconductor physics, 'n' type doping involves adding impurities to an intrinsic semiconductor to create extra negative (electron) charge carriers. This is achieved by introducing atoms with more valence electrons than the host atom.

Valence Electrons in Silicon

Silicon has four valence electrons. It forms covalent bonds with four adjacent silicon atoms to create a stable lattice structure in its natural state.

Identify the Suitable Impurity

To create 'n' type semiconductor, an impurity with more valence electrons than silicon must be added. This will introduce additional free electrons. An element with five valence electrons will provide an extra electron, leading to 'n’ type conductivity.

Key concepts

n-type semiconductor

An n-type semiconductor is a type of extrinsic semiconductor where the majority of charge carriers are electrons. The letter "n" stands for negative, indicating the predominance of these negative charge carriers. The process of creating an n-type semiconductor involves doping a pure semiconductor material, such as silicon, with a pentavalent element. These elements have five valence electrons, which is one more than silicon's four.

The extra electron from the dopant is free to move, thereby enhancing the electrical conductivity of the semiconductor. This increased electron movement allows for improved conductivity, which is essential in many electronic applications.

• n-type semiconductors are crucial for electronic devices like diodes, transistors, and integrated circuits.
• They complement p-type semiconductors to form p-n junctions, which are foundational in semiconductor technology.

valence electrons

Valence electrons are the outermost electrons of an atom and are crucial in determining how an atom interacts chemically with other atoms. In the case of semiconductor materials like silicon, the number of valence electrons plays a significant role in its conductivity properties.

Silicon atoms have four valence electrons. They form a stable structure by sharing these electrons with four neighboring silicon atoms, creating covalent bonds. This bonding forms the orderly tetrahedral lattice structure characteristic of silicon.

• Valence electron sharing creates a stable lattice in pure silicon, explaining why pure silicon is a poor conductor on its own.
• Through the process of doping, additional free charge carriers can be introduced.

silicon doping

Silicon doping is a process used to enhance the electrical properties of silicon, a material that is naturally not very conductive. This process involves introducing small amounts of impurities into the silicon to alter its electrical behavior.

For n-type doping, a pentavalent dopant such as phosphorus or arsenic is added. These elements introduce an extra valence electron into the silicon lattice, increasing the number of free electrons available for conduction.

• The extra electrons speed up the material's electrical conductivity, making it more efficient for electronic devices.
• Depending on the desired conductivity type, different dopants are used for various applications.

extrinsic semiconductors

Extrinsic semiconductors are modified forms of intrinsic semiconductors where impurities are added to alter their electrical properties. This modification turns a naturally less conductive material into one capable of efficient electrical conduction.

The two main types of extrinsic semiconductors are n-type and p-type. N-type semiconductors are created by introducing pentavalent impurities, resulting in excess electrons as charge carriers. On the other hand, p-type semiconductors are generated by adding trivalent impurities, which create holes (positive charge carriers).

• Extrinsic semiconductors are fundamental in the development of electronic devices and technology.
• They offer tailored electrical properties, making them versatile in various electronic applications.