What is a charge carrier?

A carrier is a type of object which carries a particular thing from one point to another point. For instance, people use different vehicles from one place to another, and the vehicle carries those people and acts as a carrier.

Let us take another instance; We use tiffin boxes to carry our food so in that case the tiffin box act as a carrier to carry our food.  Charge carriers are those kinds of particles that is electrons, holes, and ions which contain charge in them, and it carries charge from one place to another.  The particles that carry electric charges especially in electrical conductors are electrons, ions, or holes.

• In metals, the electrons are in majority, and only one or two electrons can move in the valence band of the structure of the metal. The electrons which are able to move are called free electrons which are termed conduction electrons.
• In electrolytes, the solution contains ions that are formed by either gaining an extra electron or by losing it so that they are electrically charged. Atoms that have gained an electron, and are negatively charged are called “Anions”, and the atoms that have lost an electron, and are positively charged are called “Cations”
• In plasma, the charge carriers are the electrons, and cations of ionized gas which is found in electric arcs, the sun, and the stars etcetera.
• In a vacuum, the electrons which are free act as a charge carrier. The mobile electronic cloud is generated by a heated metal cathode of the vacuum tube by the process of thermionic emission.
• In semiconductors, there are two types of charge carriers that are electrons, and holes that carry electric current about which we will see in detail below.

Negative charge carriers

Negative charge carriers that are electrons are those kinds of charged particles that contain negative charge in them. Electrons are the type of particles that are detached from their parent atom and move freely in space. Electrons have a charge commonly denoted as “-e” or $-1.602 \times {10}^{-19}C.$

Positive charge carriers

Positive charge carriers that are holes are those kinds of charged particles that contain positive charge in them. In a valence band, the holes are the type of empty or free spaces which can move from one place to another in the band itself. The holes are also called protons, and the charge of a proton is “+e” or $+1.602\times {10}^{-19} C$. It is important to note that the concept of the hole is a virtual concept. When an electron moves from one place to another it leaves a vacant or empty space which is referred to as a “hole”. As holes can accept free electrons so they are also called acceptors.

The electron holes pair in a semiconductor is created due to the excitation of electrons from the valence band to the conduction band. In physics, carrier generation and carrier recombination are the processes by which charge carriers are created, and also eliminated. When an electron and a hole recombine, the energy is transferred to the electron itself within the conduction band.

Majority and Minority charge carriers

The majority of carriers are those kinds of carriers that are present in a large amount. These charged carriers are responsible for the flow of electric current where electrons move from one place to another. In a semiconductor, the electrons are responsible for the flow of electric current which are also free carriers.

The minority carriers are those kinds of carriers that are present in very small quantities. They are responsible for a very small amount of electric current to flow in a semiconductor.

In the case of Field-effect Transistors (FETs), the majority and minority charge carriers are either electrons or holes but not both, because they are unipolar devices whereas Bipolar Junction Transistors (BJTs) are the bipolar device, that is, there are two types of charge carriers in BJTs.

Charge carriers in an intrinsic and extrinsic semiconductor

Intrinsic semiconductors are the pure form of semiconductors where no doping is done. In such types of semiconducting materials, the total number of free electrons is equal to the total number of holes.

Extrinsic semiconductors are formed by adding some impurities with the intrinsic semiconductors which are called “Doping”. In such types of semiconducting materials, the total number of free electrons is always greater than or smaller than the total number of holes present.

Majority and minority charge carriers in an n-type semiconductor

An n-type semiconductor is formed when the intrinsic semiconductor is doped with pentavalent atoms such as arsenic, phosphorus, etc. A large number of free electrons are present in an n-type semiconductor. The free electrons are the majority carriers in this semiconductor. Most of the electric current flows due to a large number of electrons present in it.

In n-type semiconductor very small number of vacant spaces that is holes are present. In this semiconductor, the holes are the minority carriers. The holes carry only a small amount of the electric current.

As we know the pentavalent atoms carry a greater number of free electrons so in an n-type semiconductor the total amount of electrons is greater than the total amount of holes.

Total number of electrons > Total number of holes

Majority and minority charge carriers in a p-type semiconductor

When the intrinsic semiconductors are doped with trivalent atoms like boron, gallium, etc then p-type semiconductors are formed. In this type of conductor large number of holes are present. In p-type semiconductors, the holes are the abundant charge carriers. Most of the electric current in p-type semiconductors is carried by the holes or the positive charge carriers.

In p-type semiconductors, a very small number of electrons are present which is responsible for the flow of a small amount of electric current. The electrons from the minority charge carriers in a p-type semiconductor.

As we know the trivalent atoms carry a greater number of holes that is vacant spaces so in a p-type semiconductor the total number of holes is greater than the total number of electrons present in it.

Total number of holes > Total number of electrons

Context and Applications

This topic is significant in the professional exams for undergraduate, graduate, and postgraduate courses.

• Bachelors in Electrical Engineering
• Bachelors in Electronics Engineering
• Masters in Electrical Engineering
• Masters in Electronics Engineering

Practice Problems

1. What are the two types of charge carriers?

1. Negative, and neutral
2. Positive, and neutral
3. Positive, and negative
4. Negative, and negative

Answer: Option c

Explanation: The two types of charge carriers are– positive, and negative charge carriers. The electrons are the negative charge carriers, and the holes are the positive charge carriers.

2. Which type of charge carriers are in majority of n-type semiconductors?

1. Holes
2. Electrons
3. Ions
4. Cations

Answer: Option b

Explanation: In an n-type semiconductor, the electrons are in majority. This type of semiconductor is formed by pentavalent doping of intrinsic semiconductors.

3. Which type of charge carriers are in majority of p-type semiconductors?

1. Holes
2. Electrons
3. Ions
4. Cations

Answer: Option a

Explanation: In a p-type semiconductor, the holes are in majority. This type of semiconductor is formed by trivalent doping of intrinsic semiconductors.

4. How does an electric field radiate from a positive charge?

1. Outwards
2. Inwards
3. Spiral
4. Square

Answer: Option a

Explanation: The electric field-effect is such that it radiates outwards from a positive charge. The direction of the field is from positive to negative charge.

5. How does an electric field radiate from a negative charge?

1. Outwards
2. Inwards
3. Spiral
4. Square

Answer: Option b

Explanation: The electric field radiates inwards from a negative charge. The direction of the field is from positive to negative charge.

Related Concepts

• Law of mass action
• Charge neutrality
• Drift and diffusion current
• Effect of electric current on mobility
• P-N junction theory