Semiconductor

Experiments in the 1930s led to the conclusion that certain solid – state semiconductors and their junctions had the ability to control the number of charge carriers and also control the direction of charge carrier flow through them. This led to the development of modern solid state semiconductor electronics. Semiconductors are one of the most important components of important electronic devices today.

Semiconductor

Semiconductors are the materials that are sensitive to electricity between conductors and insulators. Therefore, semiconductors are non-metals which have limited electrical conductivity. In pure form of semiconductor, some non-metals such as silicon and germanium are good semiconductors. By adding some impurities to the semiconductor, the conductivity of the semiconductor can be changed through a process called doping. Almost all electrical and electronic appliances use semiconductors to control the flow of electricity within them.

Semiconductor Definition

A semiconductor is a substance whose resistivity is between conductors and insulators. The resistivity property is not the only property which decides a material is a semiconductor. Semiconductor devices are widely used in the field of electronics. The transistor has replaced bulky vacuum tubes, reducing the size and cost of devices, and this revolution has further accelerated its pace, leading to new inventions such as integrated electronics.

Conduction in Semiconductors

Having a little knowledge about electrons, we know that the outermost shell has the valence electrons loosely associated (attached) with the nucleus. Such an atom that has valence electrons, when it approaches the other atom, the valence electrons of both atoms combine to form pairs of electrons. This bond is not so strong and is therefore a covalent bond.

Properties of Semiconductor

There are many properties of semiconductors and some of which are given here.

1. The temperature coefficient of resistance of Semiconductors is negative, which means that the resistance of a semiconductor decreases with increasing temperature and vice versa. e.g., germanium is an insulator at low temperatures, but becomes a good conductor at high temperatures.
2. Semiconductors in neutral behave like bad conductors, but there are some techniques to allow current to flow through semiconductors. Due to the doping of the semiconductor, it behaves like a conductive material and allows electricity to pass through.
3. Resistivity of a semiconductor is greater than insulator and smaller than conductors.
4. In some semiconductors, excited electrons can relax and emit light instead of generating heat. These semiconductors are used to make the light emitting diode (LED), which is the optical property of a semiconductor.

Types of Semiconductors

There are two types of semiconductors which are given here.

1. Intrinsic Semiconductor
2. Extrinsic Semiconductor

Intrinsic Semiconductor

An extremely pure form of semiconductor is known as an intrinsic semiconductor.

In an intrinsic semiconductor, the electron-hole pair is formed at room temperature. In Intrinsic semiconductor, when a voltage is applied between the material, current flows through the material because of free electrons and holes.

Free electrons are generated from the breaking of covalent bonds by thermal or heat energy. At the same time, holes are created in covalent bands. Therefore, the total current through the semiconductor is the sum of the current which is produced due to electrons and holes.

Extrinsic Semiconductor

Intrinsic semiconductors are poor conductors or have poor conductivity at room temperature. Impurities are added to the semiconductor material to increase conductivity. This type of semiconductor has some impurities called extrinsic semiconductors. 

The process of adding impurities into the semiconductor to increase the conductivity of the semiconductor is known as doping. The main aim of doping is to raise the number of electrons or holes in the semiconductor crystal. Depending on the impurities added, it can be decided between p-type or n-type semiconductors.

P – type Semiconductor

When a small amount of trivalent impurity is added to a pure semiconductor then the semiconductor is known as P-type extrinsic semiconductor. The impurity which is added has valence electrons equals to three (3).

N – type Semiconductor

When a small amount of pentavalent impurity is added in a pure semiconductor then the semiconductor is termed as N – type extrinsic semiconductor. The impurity which is added has valence electrons equals to five (5).

Mostly used Semiconductor

Many semiconductors are available, but some have practical applications in electronics. Silicon (Se) and Germanium (Ge) are broadly used semiconductors. These semiconductors are widely used because the energy these two materials require to release electrons from their valence band is too low. Silicon needs 1.1 eV and germanium needs 0.7 eV to free electrons from its conduction band. Silicon and germanium are the basic or fundamental examples of semiconductors.

Conclusion

A semiconductor is a substance whose resistivity is between conductors and insulators.

The resistivity property is not the only property which decides a material is a semiconductor.

Resistivity of a semiconductor is greater than insulator and smaller than conductors.

There are two types of semiconductors which are given here.

1. Intrinsic Semiconductor
2. Extrinsic Semiconductor

An extremely pure form of semiconductor is known as an intrinsic semiconductor.

Intrinsic semiconductors are poor conductors or have poor conductivity at room temperature. Impurities are added to the semiconductor material to increase conductivity. This type of semiconductor has some impurities called extrinsic semiconductors. 

When a small amount of trivalent impurity is added to a pure semiconductor then the semiconductor is known as P-type extrinsic semiconductor.

When a small amount of pentavalent impurity is added to a pure semiconductor then the semiconductor is known as N – type extrinsic semiconductor.

Silicon (Se) and Germanium (Ge) are broadly used semiconductors.