Extrinsic Semiconductors

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What are Semiconductors?

Semiconductors are those materials that have an electrical conductivity value which lies between that of an insulator such as glass and a conductor such as copper. The common examples of semiconductors are Silicon and Germanium which are also known as Elemental Semiconductors. The examples of Compound Semiconductors are Cds, GaAs, CdSe, anthracene, doped phthalocyanines, etc. Diodes, transistors, and integrated circuits are some of the electronic devices in which semiconductors are mainly used. The application of these devices is wide because they are quite affordable, compact, reliable, and power-efficient. There are mainly two types of semiconductors, and they are intrinsic semiconductors and extrinsic semiconductors.


What are Intrinsic Semiconductors?

Intrinsic Semiconductors (Definition) - Intrinsic semiconductors are those semiconductors that are always in extremely pure form. It is also known as an undoped semiconductor. It shows a low electrical conductivity under room temperature and its conductivity depends on its temperature. Therefore, intrinsic semiconductors are generally not used in electronic devices due to its low electrical conductivity. Examples are silicon (Si) and Germanium (Ge). An intrinsic semiconductor acts as a perfect insulator at absolute zero, which means its conductivity is zero.


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What are Extrinsic Semiconductors?

Extrinsic Semiconductors (Definition) - An extrinsic semiconductors are those semiconductors that come into existence when a measured and small amount of chemical impurity is added to intrinsic semiconductors. It is also known as doped semiconductor or impurity semiconductors. The doping of the semiconductors increases its conductivity. The process of deliberately adding a desirable impurity is known as doping and the impurity atoms are called dopants. Extrinsic semiconductors are further classified into two types - N-Type semiconductors and P-type semiconductors.


The major difference between extrinsic and intrinsic semiconductors are as follow:


Difference Between Extrinsic and Intrinsic Semiconductors

Intrinsic Semiconductors

Extrinsic semiconductors

1. Intrinsic Semiconductors are always in pure form.

1. Extrinsic Semiconductors are made by doping some impurity in the pure semiconductors.

2. They have low electrical conductivity at room temperature.

2. They have comparatively high electrical conductivity.

3. The no. of electrons are equal to the no. of holes.

3. The no. of electrons is not equal to the no. of holes.

4. It is dependent on temperature only.

4. It is dependent on temperature as well as the amount of impurity.

5. It is not classified further.

5. It is further classified as n-type semiconductors and p-type semiconductors.

6. Examples are Silicon and Germanium.

6. Examples are Si and Ge doped with Al, In, P, As, etc.


Therefore, these are some of the major differences between extrinsic and intrinsic semiconductors.


Did You Know?

Semiconductors are used in various electrical devices like computers, the internet, smartphones, tablet services. They are widely used in the present world. It would be impossible to make all these devices without semiconductors. In 1821, an effect due to semiconductors was first noticed by Thomas Johan Seebeck. Studies regarding semiconductors were carried out in the laboratories in the early 1830s.


In 1833, Michael Faraday experimented with silver sulfide and discovered that the conductivity of silver sulfide increased with the increase of temperature. This behaviour of silver sulfide is opposite to the metals such as copper in which its conductivity decreases with an increase in temperature.

FAQ (Frequently Asked Questions)

1. What are N-type Semiconductors?

Ans: N-type semiconductors are those extrinsic semiconductors in which a tetravalent element (elements that have valency 4) such as Silicon or Germanium is doped with a pentavalent element (elements that have valency 5) such as Arsenic (As), Antimony (Sb). As a result, an atom of that pentavalent element occupies the position of an atom in the crystal lattice of the tetravalent element. When the doping is done, four out of five electrons of the pentavalent atom bonds with the four tetravalent element neighbours, and the fifth electron forms a weak bond with the parent atom.


Therefore, a very low amount of ionisation energy is required to set the fifth electron free. Also, the fifth electron moves freely in the lattice of the tetravalent element, even if it is at room temperature.

2. What are P-type Semiconductors?

Ans: P-type semiconductors are those extrinsic semiconductors in which a tetravalent element such as Silicon and Germanium is doped with a trivalent element ( elements that have valency 3) such as Aluminium (Al), Indium (In), etc. When the doping is done, three out of four electrons of the tetravalent element forms a covalent bond with the three electrons of the trivalent element. A deficiency of one electron arises, and therefore the fourth electron does not have an electron to bond with.


Thus, a vacancy or hole gets created, and a need arises to fill that vacancy. Hence, there is a chance for an electron in the outer orbit of a neighbouring atom to jump and fill the vacancy. Thus, this creates a hole or vacancy in the place of that electron. As a result, the hole becomes available for conduction.