Extrinsic Semiconductor: Definitions, Examples, Facts, Types, Uses, and Sample Questions

Extrinsic Semiconductor Overview

Extrinsic semiconductors are created when intrinsic semiconductors are combined with a trace quantity of a chemical impurity. Doped semiconductors or impurity semiconductors are other names for them. In general, semiconductors are crystalline or amorphous substances with electrical conductivity between a conductor and an insulator. Doping changes the semiconductor's electrical characteristics, making it suitable for use in electronic devices like diodes and transistors. 

What are Semiconductors?

Semiconductors are substances that fall between insulators like glass and conductors like copper in terms of electrical conductivity. Silicon and Germanium, commonly referred to as elemental semiconductors, are typical examples of semiconductors. Examples of compound semiconductors include phthalocyanines with dopants, anthracene, GaAs, CdSe, and CdS. Semiconductors are mostly used in electronic devices such as transistors, integrated circuits, and diodes. These gadgets have a wide range of uses since they are reasonably priced, small, dependable, and power-efficient. Extrinsic semiconductors and intrinsic semiconductors are the two primary categories of semiconductors.

What is an Extrinsic Semiconductor?

Extrinsic semiconductors are those semiconductors that are created when an intrinsic semiconductor is combined with a controlled and limited amount of chemical impurity. Impurity semiconductors, or doped semiconductors, are other names for them. The conductivity of semiconductors is increased through doping. Doping is the purposeful addition of an undesirable impurity, and dopants are the impurity atoms. N-Type semiconductors and P-Type semiconductors are the two other forms of extrinsic semiconductors.

Examples of an Extrinsic Semiconductor

Pure silicon and germanium doped with impurities like As, P, Bi, Sb, In, B, Al, etc. are examples of extrinsic semiconductors.

Facts about Extrinsic Semiconductor

1. Michael Faraday conducted experiments with silver sulfide in 1833 and found that the conductivity of the substance increased as the temperature rose.
2. Computers, the internet, cell phones, and tablet services are just a few of the electrical gadgets that employ semiconductors.
3. Thomas Johan Seebeck first noted a semiconductor-related phenomenon in 1821.  
4. In the modern world, they are commonly used. 
5. Without semiconductors, it would be impossible to manufacture all of these gadgets. 
6. In the early 1830s, studies on semiconductors were conducted in labs. 
7. This behavior of silver sulfide contrasts with that of metals like copper, whose conductivity diminishes as the temperature rises.

Read more about the Drift Velocity Formula.

Types of Extrinsic Semiconductors

The following are the two types of extrinsic semiconductors-

N-Type Semiconductors

By doping an inherent semiconductor with an electron donor element during production, N-type semiconductors are produced. The word "n-type" refers to the electron's negative charge. Electrons make up the bulk of carriers in n-type semiconductors, whereas holes make up the minority. For n-type silicon, phosphorus or arsenic are frequent dopants. The Fermi level of an n-type semiconductor is higher than that of an intrinsic semiconductor and is located nearer the conduction band than the valence band.

Examples: Phosphorus, arsenic, antimony, etc.

P-Type Semiconductors

An intrinsic semiconductor is doped during production with an electron acceptor element to produce P-type semiconductors. The positive charge of a hole is referred to as its p-type. P-type semiconductors have a higher hole concentration than electron concentration in comparison to n-type semiconductors. Electrons make up the minority of carriers in p-type semiconductors, whereas holes constitute the majority. Boron or gallium are frequently used as p-type dopants for silicon. The Fermi level for p-type semiconductors is below the intrinsic level and is situated nearer the valence band than the conduction band.

Examples: Boron, Aluminum, Gallium, etc.

Extrinsic vs Intrinsic Semiconductor

The main distinctions between intrinsic and extrinsic semiconductors are shown in the table below-

Uses of Extrinsic Semiconductor

The majority of electronic gadgets are made mostly of extrinsic semiconductors. The following are some of the uses of extrinsic semiconductors-

1. A P-N junction is created when semiconductors of both P and N types come together.
2. Bipolar junction transistors and field-effect transistors both employ extrinsic semiconductors.
3. Electronic gadgets use diodes because they need a certain unidirectional current flow.
4. The majority of extrinsic semiconductors are switched.

Points to Remember

1. Pentavalent and trivalent dopants can be used to dope extrinsic semiconductors.
2. P-type or N-type extrinsic semiconductors are both possible.
3. A semiconductor's overall neutrality is unaffected by doping.
4. Due to their capacity for unidirectional current flow, extrinsic semiconductors are mostly used in electrical devices.
5. In P-Type semiconductors, holes make up the majority of the charge carriers.
6. In N-Type Semiconductors, the bulk of the charge carriers are electrons.
7. A pure/intrinsic semiconductor is doped with a certain concentration of impurities to create an extrinsic semiconductor.

Sample Questions related to Extrinsic Semiconductor

Sample Question 1: What dopants are trivalent and pentavalent. Give instances. 

Solution: Pentavalent dopants are atoms that have five valence electrons. They are employed in the production of N-Type semiconductors by doping semiconductors.Examples include arsenic (As), phosphorous (P), and antimony (Sb). The term "trivalent dopants" refers to atoms containing three valence electrons. Consider the elements aluminium (Al) and boron (B).

Sample Question 2: What are dopants, and what is doping? 

Solution: Doping is the technique of introducing certain impurities to an intrinsic semiconductor in order to increase the carrier concentration. Dopants are atoms that are employed as an impurity. 

Sample Question 3: What happens when a pure semiconductor is contaminated by a pentavalent impurity?

Solution: An N-Type Extrinsic Semiconductor is created when a pentavalent impurity is added to an intrinsic semiconductor.

Sample Question 4: What causes doping in semiconductors?

Solution: Extrinsic semiconductors are ones that have certain impurities doped into them. The impurity modifies the semiconductor's electrical characteristics, improving its suitability for electronic components like diodes and transistors. The dopant that is added to the material is selected in a way that prevents distortion of the initial lattice of the pure semiconductor. When a tiny amount of an appropriate impurity is introduced to a pure substance, the conductivity of the mixture is multiplied by many.  Since the dopants only occupy a small portion of the original semiconductor's crystal, it is essential that their size be approximately identical to that of the semiconductor atoms.

Sample Question 5: How do semiconductors work? 

Solution: The answer is that semiconductors are crystalline solids with electrical conductivities that lie between those of insulators and conductors. In semiconductors, the energy gap between the valence and conduction bands is rather tiny. Compared to conductors, semiconductors make it a bit harder for electrons to get up to the conduction band.

Sample Question 6: Describe the components of a good semiconductor.

Solution: The tiny energy band gaps of elements like silicon and germanium make them good conductors. Additionally, because they are both tetravalent elements, they each have four valence electrons.

Sample Question 7: What are Extrinsic Semiconductors, you ask?

Solution: When certain impurities are added to a pure semiconductor, extrinsic semiconductors are produced. Semiconductors come in two varieties: P-type and N-type.