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Difference between Intrinsic and Extrinsic Semiconductor
Semiconductor devices are extensively used in the field of electronics. A semiconductor is a substance whose resistivity lies between conductors and insulators. Semiconductors have negative temperature co-efficient. The resistance in semiconductors increases with the decrease in temperature and vice versa. The conducting properties of a semiconductor changes, when a suitable metallic impurity is added to it.
In this article, we will highlight the major differences between intrinsic and extrinsic semiconductors by considering different parameters such as doping level, conductivity, charge density, etc.
What is an Intrinsic Semiconductor?
A semiconductor material in its pure form is known as an intrinsic semiconductor. Thus, the intrinsic semiconductors are chemically pure, i.e. they are free from impurities.
In case of intrinsic semiconductors, the number of charge carriers, i.e., holes and electrons are determined by the properties of the semiconductor material itself instead of the impurity. Also, the number of free electrons is equal to the number of holes in the intrinsic semiconductor. The common examples of the intrinsic semiconductors are germanium (Ge) and silicon (Si).
What is an Extrinsic Semiconductor?
When a small amount of chemical impurity is added to an intrinsic semiconductor, then the resulting semiconductor material is known as extrinsic semiconductor. The extrinsic semiconductor is also known as doped semiconductor. The process of adding impurity in the intrinsic semiconductor is known as doping. The doping of semiconductors increases their conductivity
Based on the type of doping, the extrinsic semiconductors are classified into two types viz. N-type semiconductors and P-type semiconductors. When a pentavalent impurity is added to an intrinsic semiconductor, then the resulting semiconductor is termed as N-type semiconductor. On the other hand, when a trivalent impurity is added to a pure semiconductor, then the obtained semiconductor is known as P-type semiconductor.
Difference between Intrinsic Semiconductor and Extrinsic Semiconductor
The following table highlights the major differences between an intrinsic semiconductor and an extrinsic semiconductor −
| Parameter | Intrinsic Semiconductor | Extrinsic Semiconductor |
|---|---|---|
| Definition | The semiconductor in its pure form is known as intrinsic semiconductor. | When a chemical impurity is added to an intrinsic semiconductor, then the resulting semiconductor is known as extrinsic semiconductor. |
| Types | There is no classification of intrinsic semiconductor. | Based on the impurity added, the extrinsic semiconductors are of two types viz. P-type semiconductor and N-type semiconductor. |
| Doping | In case of intrinsic semiconductor, there is no doping or addition of impurity. | In an extrinsic semiconductor, the doping is performed, i.e. a small amount of impurity is added in the pure semiconductor. |
| Charge carrier density | In an intrinsic semiconductor, the number of electrons is equal to number of holes. | In case of extrinsic semiconductors, the number of holes and electrons are not equal. In a P-type semiconductor, the holes are more than electrons while in an N-type semiconductor, the electrons are more than holes. |
| Conductivity | The electrical conductivity of intrinsic semiconductors is low. | The extrinsic semiconductors have high electrical conductivity. |
| Dependency of conductivity | The conductivity of intrinsic semiconductor is dependent on temperature only. | The conductivity of extrinsic semiconductor is dependent on temperature as well as amount of impurity added. |
| Conductivity at 0 Kelvin | The intrinsic semiconductor does not conduct at 0 Kelvin temperature. | The extrinsic semiconductor conducts at 0 Kelvin temperature. |
| Cause of charge carrier production | In the intrinsic semiconductors, the charge carriers are produced only due to thermal agitation. | In case of extrinsic semiconductors, the charge carriers are produced due to thermal agitation as well as chemical impurities added to the semiconductor. |
| Operating temperature | Intrinsic semiconductors have low operating temperature. | The operating temperature for extrinsic semiconductors is high. |
| Fermi level | At 0 Kelvin, the Fermi level in intrinsic semiconductors exactly lies between conduction band and valance band. | At 0 Kelvin, the Fermi level in extrinsic semiconductor depends upon the types of semiconductor, i.e. in case of N-type semiconductor, it lies closer to conduction band and in the P-type semiconductor, it lies closer to valance band. |
| Ratio of charge carriers | In an intrinsic semiconductor, the ratio of majority and minority charge carriers is 1. | In case of extrinsic semiconductor, the ratio of majority and minority charge carriers is not unity. |
| Examples | The crystalline forms of pure silicon and germanium are the examples of intrinsic semiconductors. | The examples of extrinsic semiconductors are pure silicon and germanium doped with chemical impurities like As, P, Bi, Sb, In, B, Al, etc. |
Conclusion
From the above comparison, it can be concluded that intrinsic semiconductors are quite different from extrinsic semiconductors in many aspects like charge density, doping, types, conductivity, etc.
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