CLASSIFICATION OF MATERIAL BASED ON BAND GAP

Classification of material  based on band gap is classified in three categories that are insulators, conductors and semi-conductors.

CLASSIFICATION OF MATTER BASED ON FORBIDDEN GAP
CLASSIFICATION OF MATERIAL BASED ON BAND GAP

CLASSIFICATION OF MATERIAL BASED ON BAND GAP

INSULATORS

The material which does not readily conduct electricity because the forbidden gap (band gap) in insulator is very high, approx 15 eV (electron volt). Insulators are also called poor conductors of electricity.

Insulator band gap

Normally, in insulators valance band is fully occupied with electrons and conduction band is empty that is no electron present in conduction band.

In order to move electron from valance band to conduction band a large amount of external energy is required which must be equal to the forbidden gap, only then current will flow.

For examples: Rubber, wood, plastic, thermocol, glass etc.

CONDUCTORS

The material which easily allows electric current to flow through them are called as conductors. In conductors valance band and conduction band overlap each other. Therefore, there is no forbidden gap in conductors.

conductor band gap

Normally, in conductors valance band is partially occupied with electrons and in conduction band large number of electrons are present.

In order to move electron from valance band to conduction band a small amount of external energy is enough. Therefore more number of electrons can easily move to the conduction band. When valance band electrons move to conduction band they become free electrons.

For example: Metal such as aluminium, iron, copper, silver etc.

SEMICONDUCTOR

The first semiconductor device was invented by Jagadis Chandra Bose in 1901 named as “Cat whiskers”, it was a point-contact semiconductor rectifier used for detecting radio waves. A transistor is a device or electronic component composed of semiconductor material. William Shockley, John Bardeen & Walter Brattain all three co-invented the transistor in 1947 at Bell Labs.

The material which behaves like both conductor as well as insulator is called semiconductor, because, In insulator small forbidden gap is present, approx 1.3 eV (electron volt) unlike conductor which has no forbidden gap and insulator which has large forbidden gap.

Semiconductor band gap

At low temperature, the valance band is completely filled by electrons and conduction band is empty, that’s why behaves like an insulator at room temperature.

At room temperature, electrons in the valance band get enough energy in the form of heat and few electrons moves from valance band to conduction band.

So, when the temperature goes increasing, the number of electrons moving from valance band to conduction band also increases. This shows that electrical conductivity of semiconductor increases with increase in temperature or any form of energy in the material.

For example : Silicon, germanium, graphite etc.

In semiconductor valance band is fully occupied with electrons and conduction band is empty that is no electron present in conduction band.

In order to move electron from valance band to conduction band a large amount of external energy is required which must be equal to the forbidden gap, only then current will flow.

For examples: With such a small gap, the presence of a small percentage of a doping material can increase the conductivity dramatically.

ENERGY BAND GAP OF DIFFERENT MATERIALS

Material

Energy gap (eV) at

0 K 300 K
Si 1.17 1.11
Ge 0.74 0.66
InSb 0.23 0.17
InAs 0.43 0.36
InP 1.42 1.27
GaP 2.32 2.25
GaAs 1.52 1.43
GaSb 0.81 0.68
CdSe 1.84 1.74
CdTe 1.61 1.44
ZnO 3.44 3.2
ZnS 3.91 3.6

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