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Semiconductors are divided into two categories: intrinsic semiconductors and extrinsic semiconductors. So, here in this topic, we will briefly study intrinsic semiconductors, their making, and their uses. We will also cover the significant difference between intrinsic and extrinsic semiconductors.
Semiconductors which are pure and impurities free known as the intrinsic semiconductors. In this semiconductor category, no. of electrons are equal to the no. of holes. Go through the complete notes to secure good marks from this topic in your examinations.
Intrinsic Semiconductor
A semiconductor is a material whose conductivity falls between a conductor and insulator. Based on its impurity, the semiconductor has been classified into two parts: intrinsic semiconductors and extrinsic semiconductors. In intrinsic semiconductors, there is no other intentionally doped material (similar to mixing). For Example, Silicon (Si), Germanium (Ge) are some of them.
Atomic No. and Electronic Configuration of Si and Ge are as follows:-
| Element | Atomic Number | Electronic Configuration |
| Silicon | 14 | 1s22s22p63s23p2 |
| Germanium | 32 | 1s22s22p63s23p63p63d104s24p2 |
The above table indicates that Si and Ge have four remaining electrons in outermost orbitals, i.e., valence shells. These electrons are called valence electrons and are responsible for the conduction properties of the semiconductors.
What is an intrinsic semiconductor?
Intrinsic semiconductors, also referred as pure or undoped semiconductors, are flawless semiconductor crystals that are free of other elements’ flaws and impurities. All semiconductor materials, including those doped with other components, have intrinsic features, with the doping components introducing other desired qualities.
Intrinsic means inherent and natural, and the intrinsic semiconductors show the bulk features of semiconductor substances themselves, not the impurities and dopants. As silicon and germanium are elemental semiconductors, they are most widely used as intrinsic semiconductors. They were among the first semiconductors to be widely researched and utilised. Semiconductors’ distinctive features are founded on their electrical structure. The electrical structure, which determines semiconductors’ essential properties, is one of the mechanisms that distinguish semiconductors as a distinct kind of material.
What are Extrinsic semiconductors?
The conductivity of the semiconductors can be improved with the help of a small number of suitable atoms known as the impurity. The process that involves adding impurities to the pure semiconductor is called doping. Generally, one atom in 10^7 will be replaced by a dopant atom in a doped semiconductor.
An extrinsic Semiconductor is divided into two types:
- N-type Semiconductor.
- P-type Semiconductor.
Properties N-type semiconductor
- It mainly occurs due to elections
- Completely neutral
- I = Ie and ne >> nh
- Majority- electrons and minority – holes.
When a pure semiconductor (Si & Ge) is doped in the pentavalent impurity (Sb, As, Bi, P), you will notice that four electrons out of five valence bonds will create a bond with the four electrons of Si and Ge.
The fifth electron of the dopant will be free. In that case, an impure atom will donate one free electron for the conduction in the lattice is known as Donar.
Then the no. of electrons will increase with the addition of an impurity. Then the negative charge carrier will increase. Hence this is called an N-type semiconductor.
Crystal will always act neutral, but the donor atom will automatically become an immobile ion. As conduction occurs to free many electrons, electrons found in the N-type semiconductor have majority carriers, and the holes are the minority carriers.
Properties of P-type semiconductor
- It mainly occurs due to holes.
- Completely neutral.
- I = Ih and nh >> ne
- Majority – holes, and minority – Electrons.
Whenever a pure semiconductor is doped with the trivalent impurity (B, Ge, Al, In), then three valence electrons of the impurity bonds make a bond with the four valence electrons of the semiconductor.
In this case, the electron will be absent from the impurity. These impurity atoms, now ready to accept bonded electrons, are known as acceptors.
With the increase of impurity, the hole will also increase; hence it is called the P-type semiconductor.
What is the difference between intrinsic semiconductors and extrinsic semiconductors?
| Intrinsic semiconductors | Extrinsic semiconductors |
| It is a pure semiconductor. | It is an impure semiconductor. |
| Electron density is equal to the density of holes. | Electron density is not equal to the density of holes. |
| Electrical conductivity is low. | Electrical conductivity is high. |
| Depending on the temperature. | It also depends on temperature, but it also depends on impurity. |
| No impurities. | Trivalent impurity, pentavalent impurity. |
Conclusion
The semiconductor is broadly categorised into two types: Intrinsic semiconductors and Extrinsic semiconductors. They are further classified into P and N-type semiconductors. The intrinsic semiconductor becomes an insulator at 0K(−273 ∘C) as the motion of free electron stops, which means there is no electron in the conduction band. Silicon (Si) and Germanium (Ge) are examples of intrinsic semiconductors. This belongs to the fourth group of the periodic timetable, and their atomic numbers are fourteen and thirty-two. This is one of the essential electronics topics from the examination point of view.
