Introduction

This chapter will discuss semiconductors, how it works, and their principle. We will study two types of semiconductors: intrinsic and extrinsic semiconductors. We all know that semiconductors are a type of crystalline solids that have conductivity between conductors and insulators. It helps electricity to flow through it. This crystalline solid gets its conductivity due to impurity, or it might become conductive due to the temperature change. The phenomenon of adding impurities is known as doping. Extrinsic semiconductor is one of the most important topics of electronics. 

What are semiconductors?

Semiconductors are devices that are neither conductor nor insulator. The conductivity of a semiconductor is changed by doping. There are mainly two types of semiconductors those lists are as follows:

1. Intrinsic semiconductors
2. Extrinsic semiconductors

Intrinsic semiconductors

Intrinsic semiconductors receive their conductivity property through the surrounding temperature. At room temperature, you will find that intrinsic semiconductor has low conductivity. Though we now know that it has common conductivity properties, due to this reason, this semiconductor is unstable in any electronic device.

Extrinsic Semiconductor

Extrinsic semiconductors come into existence when a small number of chemical impurities are added to intrinsic semiconductors. It is also called doped semiconductors. The doping in semiconductors increases their conductivity. Extrinsic semiconductors are further categorised into two types, i.e., N-Type and P-Type semiconductor. The extrinsic semiconductors become intrinsic at very high temperatures because band to band transition dominants over impurity ionisation.

What is doping?

Doping is one of the most important parts; it intentionally adds impurities so that semiconductors become highly conductive and typically work at any temperature. This process increases the conductivity of the Extrinsic Semiconductor.

Why were all the semiconductors doped?

Semiconductors like the Extrinsic Semiconductor are developed with the help of doping; it adds impurities to this semiconductor so that it can be more conductive. Impurities can improve the electrical property of semiconductors to make them more stable. They can easily be used in electronic appliances like diodes, transistors, and other electronic equipment.

Important note: A small portion of impurities have been added to the pure metal while adding impurities. The purpose of adding these impurities to the pure metal is to increase the conductivity so that electricity can easily flow through it. Extrinsic semiconductors can be the doped Semiconductor or the impure Semiconductor.  

Atoms that have been used in the doping process are also called dopants. Impurity helps create more electrical conductivity in the semiconductors like diodes and transistors. So, these devices can perform well in any electronic device.

Whatever atoms (dopant) that will be added to the material are already chosen or selected to protect the original lattice of the semiconductor. Dopants only occupy a few spaces of the initial semiconductor. It is necessary because the size of the dopant is almost equal to the size of the semiconductor’s atom.

Which dopants are used more typically in the Extrinsic Semiconductor?

In the process of doping, tetravalent atoms like the Si and Ge, from their two types of dopants, are mainly found, and that dopants used in this process of doping, those dopants are as follows:

• • Pentavalent atoms; Valency of this atom is about 5. Examples of these atoms are Antimony (sb), Phosphorus (pi), Arsenic (As), and many other atoms can be found.

• Trivalent Atoms: The valency of this atom is 3. Examples of these types of atoms are Boron (B), Aluminium (A), Indium (In), and many more are on the list.

Using these dopants gets the exact size of the atoms compared to the semiconductor atoms. We all know Silicon and the Germanium belong to the fourth group that can be found on the periodic table. Now, we know that the size of the dopants from the third or the fifth group will be more viable than the fourth group. Hence it proves that the size of the atoms is more similar to the fourth group of the timetable.

From this dopant, we found two crucial Extrinsic Semiconductor those are as follows:

1. N-type semiconductor (+)
2. P-type semiconductor (-)

What is compensation doping?

Extrinsic semiconductors or the extrinsic doping on any semiconductor is doped with P-type or N-type dopants. In this case, it will easily be possible to dope both the dopants into the same material. This type of doping is known as compensation doping. This type of doping is used when junctions need to be created for electronic devices or appliances. 

If you want to develop a P-N junction, you need to take the sample of N-type doped you have to choose after that, you need to compensate for the p-type doped, or you can interchange vice versa. If both donors and acceptors are found in the semiconductor, then one with a high concentration will dominate. The final material might be N-type or P-type.

Conclusion

Semiconductors are one of the crucial topics of electronics. From above, it is clear that semiconductors are essential topics from an examination point of view. There are two types: extrinsic semiconductors and intrinsic semiconductors. The doping in the semiconductors increases their conductivity. Extrinsic semiconductors are further classified into two types, i.e., N-Type and P-Type semiconductor. The extrinsic semiconductors become intrinsic at very high temperatures because band to band transition dominants over impurity ionisation.