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# classification of materials based on energy band diagram

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## Classifying solids based on energy bands

Based on energy bands, solids are classified as conductors (metals), semiconductors, and insulators. Let us understand the topic in detail here.

## Classification of Solids Based on Energy Bands

Based on energy bands, solids are classified as conductors (metals), semiconductors, and insulators. Let us understand the topic in detail here.

### TABLE OF CONTENT

Band theory

Classification of solids based on energy bands

Conclusion

Conductors are materials that allow the flow of electric charge, also known as electric current. The most common conductors are made of metal. Such materials allow current to flow due to the presence of free electrons or ions that begin to move when voltage is applied. The electrical resistance of the conductor is comparatively low and increases as the temperature rises.

Semiconductors are materials that conduct electricity between conductors and insulators. You can block or allow the flow of electricity to gain complete control over the flow of electricity. They are mainly modified by adding impurities, which is called doping. This changes characteristics such as unidirectional current flow, amplification, and energy transformation. Electrical conduction in a semiconductor is based on the movement of electrons and positions (holes).

Insulators are materials that have very high electrical resistance and do not carry current. Since the insulator has no free electrons, it does not conduct electricity. Therefore, they help protect against impact.

## Band theory

The most popular explanation for discrepancies in conduction is band theory. The ‘band’ of a material is used for explaining a variation in its physical properties of conduction.

Within the limits of energy, electrons orbit the positive nucleus of a single atom. Energy levels in many atoms reorganise into two bands, the valence band and the conductive band. The lower level of electrons is in the valence band, and the higher level of electrons is in the conduction band.

There is an energy gap between the bands where electrons cannot exist. Electrons move when conduction occurs, and for this to happen, there must be spaces in the energy bands for the electrons to move into.

## Classification of solids based on energy bands

### Conductors

Definition

Conductors are materials that allow current to flow easily.

When conductors and semiconductors are compared, conductors enable better current flow, and are said to be good electrical conductors.

Categories of conductors

Metals

Most conductive materials used in practical applications are metals. For example, the wiring used in a house probably employs copper wire or its alloy as a conductive material. The electric plug contains metal, and the internal mechanism of the electric iron also uses metal as a conductive material. This is because metals have many free electrons and promote mobility. A few of the best metal conductors are silver (Ag), copper (Cu), and gold (Au).

Nonmetals

Some nonmetals are very good conductors of electrical energy. For example, carbon in the form of graphite is a very good conductor. Looking at the structure of graphite, only three of the four carbon atoms are used for bonding. This releases the electrons and binds them together. Most nonmetals are poor conductors of electricity.

Ionic conductors

Conductors in a solution form are known as ionic conductors. For example, saltwater is an ionic solution and is an excellent electrical conductor.

### 2. Semiconductors

Definition

Semiconductors are materials that exhibit conductivity between conductors or metals and non-conductors or insulators. Semiconductors are mixtures such as gallium arsenide or pure components such as germanium and silicon.

Categories of semiconductors

Intrinsic semiconductors: Intrinsic semiconductor materials are chemically very purely made. They consist of only one element type. When the temperature rises due to collision, some electrons move freely in the lattice without being bound and do not exist in their original positions (holes). These free electrons and holes contribute to the conduction of electricity in the semiconductor. The number of negative and positive charge carriers is the same.

Extrinsic semiconductors: The conductivity of semiconductors can be significantly improved by introducing a small number of suitable surrogate atoms called impurities. The process of adding foreign atoms to a pure semiconductor is called doping.

### 3. Insulators

Definition

Electrical insulators are different from conductors. Conductors are materials that propagate the ease of current flowing through them. They allow charges to flow easily. Insulators, on the other hand, are materials that do not allow electric charges to flow freely.

Application

Insulators are primarily used when it is necessary to prevent the flow of charge. These materials act as effective insulators because they do not have the moving charge required to propagate the current. Electrical insulators are mainly used as parts of electrical equipment.

## Conclusion

While the classification of solids is done based on band energy into conductors, semiconductors, and insulators, they all have their respective applications in different fields. Examples of conductors are gold, silver, aluminium, and copper; semiconductors are gallium arsenide, germanium, and silicon; and insulators include rubber, plastic, wax, and wood.

## Classification of material on the basis of energy band materials

On the basis of energy band materials are classified as insulators, conductors, and semiconductors.

## Chapter:

Chapter: Classification of material on the basis of energy band materials

On the basis of energy band materials are classified as insulators, conductors, and semiconductors.

On the basis of energy band materials are classified as insulators, conductors, and semiconductors.

Insulators: Substance like wood, glass, which do not allow the passage of current throughthem are known as insulators. The valence band of these substances is full whereas the conduction band is completely empty. The forbidden energy gap between valence band and conduction band is very large (8ev) as shown in the fig (a). Therefore a large amount of energy, i.e. a very high electric field is required to push the valence electrons to the conduction band. This is the reason, why such materials under ordinary conditions do not conduct at all and are designated as insulators.Conductors: Substances like copper, aluminium, silver which allow the passage of currentthrough them are conductors. The valence band of these substances overlaps the conduction band as shown in fig (b). Due to this overlapping, a large number of free electrons are available for conduction. This is the reason, why a slight potential difference applied across them causes a heavy flow of current through them.Semiconductors: Substances like carbon, silicon, germanium whose electrical conductivitylies in between the conductors and insulators are known as semiconductors. The valence band of these substances is almost filled, but the conduction band is almost empty. The forbidden energy gap between valence and conduction band is very small (1ev) as shown in fig ( c ). Therefore comparatively a smaller electric field is required to push the valence electrons to the conduction band. This is the reason, why such materials under ordinary conditions do not conduct current and behaves as an insulator. Even at room temperature, when some heat energy is imparted to the valence electrons, a few of them cross over to the conduction band imparting minor conductivity to the semiconductors. As the temperature is increased, more valence electrons cross over to the conduction band and the conductivity of the material increases. Thus these materials have negative temperature co-efficient of resistance.

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## Material Classification based on Energy Band Diagram

Band Gap Theory Contents show Band Gap Theory 1. Conductor 2. Insulator 3. Semiconductor The Band Gap theory explains the mechanism of conductor, insulators and semiconductor regarding the movement of free electrons from valence band to the conduction band. An energy band which separates the conduction band and the valence band is called Band gap ... Read more

## Material Classification based on Energy Band Diagram

April 17, 2018 by Electricalvoice

## Band Gap Theory

Contents show

The Band Gap theory explains the mechanism of conductor, insulators and semiconductor regarding the movement of free electrons from valence band to the conduction band.

An energy band which separates the conduction band and the valence band is called Band gap or Forbidden band or Forbidden gap.

Based on energy gap, the material is classified into three categories

Conductor Insulator Semiconductor

The fig. 1 shows the Classification of material based on energy band theory.

Fig. 1 Classification of material based on energy band theory (e– = electrons and o = holes)

## 1. Conductor

In a conductor, there is a large number of free electrons at room temperature, so energy gap does not exist. The valence band and the conduction band overlap with each other.

Example: silver, copper, aluminium, gold, iron, steel, etc.

## 2. Insulator

In insulators, the energy gap is very high i.e. 7 eV (electron volt). So at a very high-temperature or voltage, electrons can not move from valence band to conduction band. So this material can not conduct at all.

Example: wood, paper, mica, plastic, etc.

## 3. Semiconductor

In a semiconductor, at absolute zero temperature, the conduction band is empty and it behaves like an insulator. At a normal temperature, some electrons move from valence band to conduction band. Hence, a semiconductor can conduct partially at normal or room temperature.

As temperature increases, energy gap decreases and a large number of free electrons are available.

Example: Silicon, germanium, etc.

At room temperature, the energy gap of silicon and germanium is 1.12 eV and 0.78 eV, respectively.

Semiconductors are the materials with the electric conductivity less than conductors (metals) and more than insulators.

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