Doped Semiconductors

First of all, let us know what semiconductors are? The property between the conductor and insulator is known as a semiconductor; in simple words, Semiconductors possess specific electrical properties. semiconductors made from pure silicon or germanium are rare. It is necessary to add controlled amounts of impurities to semiconductors to make them usable. Conductors with impurities change their ability to conduct electricity and act as semiconductors. When we add impurity to an intrinsic or pure material, the process is known as doping. The immunity which we add in pure material is known as a dopant. There are various methods of doping. Moreover, by reading this article you will gain more knowledge about doped semiconductors.

Doped Semiconductor

When we add a foreign atom to a crystal lattice of silicon or germanium in a small amount, it produces N-type and P-type semiconductors due to dynamic changes in their electrical process. 

The presence of dopants can change the ability of a semiconductor to conduct electricity. Low or light doping is defined as the addition of one dopant atom per 100 million atoms. A high doping level occurs when there is more than one dopant atom per ten thousand atoms. Usually, n+ stands for n-type doping, and p+ stands for p-type doping. 

The process of adding impurities to semiconductors to change their properties is known as doping. Basically, silicon and germanium are doped through the use of trivalent and pentavalent elements.

Methods of doping 

To dope the semiconductor, you need to follow the below-given methods:

1. Add the impurity atoms in the semiconductor in the molten state.
2. Heat the semiconductor in the atmosphere, which includes dopant atoms or molecules. This must be done to make it easy for the dopant molecules to diffuse into the semiconductor.
3. Implant the dopant atom by Bombarding the semiconductor with the dopant atoms or molecules.

Types of Impurities

If we talk about impurities, two types of impurities can be added to the semiconductor. They are pentavalent and trivalent impurities.

Pentavalent impurities

The pentavalent impurity atom has five valence electrons. These five valence electrons are named Nitrogen (N), Phosphorus (P), Arsenic (As), Antimony (Sb), and Bismuth (Bi).

Trivalent impurities

The Trivalent impurity atom has three valence electrons. The various examples of trivalent impurities include Boron (B), Gallium (G), Indium(In), and Aluminum(Al). 

Difference between Pentavalent impurities and trivalent impurities.

Pentavalent impurities have five valence electrons and belong to group 15. They form an n-type semiconductor when doped with a semiconductor.

Group 13 impurities contain three valence electrons and are trivalent. Doping forms a semiconductor with a lot of holes when it is doped with a semiconductor.

Effect of Doping on N-type Material

The effect of doping on an N-type material is as follows −

• As compared to intrinsic material, N-type material has extra or free electrons.
• In N-type material, all atoms are electrically neutral and are not negatively charged.
• Extra electrons are free to move through the crystal structure as they do not take part in the covalent bond process.

Compared to intrinsic silicon, N-type semiconductors contain many times more electrons than electron-hole pairs. There is a distinct difference in the electrical conductivity of this material at room temperature. It contains an abundance of current carriers. In this type of material, electrons are responsible for most of the flow of current. Extrinsic materials, therefore, become good conductors of electricity.

Effect of Doping on P-type Material

The effect of doping on a P-type material is as follows −

• Three valence electrons are present in this type of dopant material. They are actively seeking a fourth electron.
• Each hole in a P-type material can be filled with an electron. From the neighbouring covalent bonded groups, electrons require a very little amount of energy to fill the hole.
• In P material, holes are usually much more common an electron-hole pairs in pure silicon, which is typically doped with 1 to 106 doping materials.
• In the electrical conductivity of this material, there is a very determined characteristic difference at room temperature. 

To form P-type material, you have to add Indium (In) or Gallium (Ga) in pure silicon. In P-type material, the electron fills the hole, and then the hole becomes a void.

Conclusion : 

Semiconductors are materials that have the property of conductivity between conductors and non-conductors. There are two types of semiconductors. These are intrinsic semiconductors and extrinsic semiconductors. Extrinsic semiconductors are further classified as N-Type and P-Type conductors. Among the N-Type and P-Type conductors, the N-Type is considered to be the better choice due to its increased durability, and also it has a better performance compared to the p-type semiconductor. Also, the n-type semiconductor is mostly preferred because it has higher mobility, and hence we get more current compared to the p-type semiconductor.