Intrinsic and Extrinsic Semiconductors in tamil

Silicon and Germanium Atomic structure

ATOMIC STRUCTURE
According to modern theory, matter is electrical in nature. All the materials are composed of very tiny particles called atoms. The atoms are the root cause for all the matter or material existing in this world.
The atom consists of a central nucleus, contains protons and neutrons.
positively charged particle, where neutron does not have any charge.
There is yet another particle called electrons which is negative in charge and it is not reside inside the nucleus rather revolving around the nucleus. This is termed as extra nucleus.

The character of any atoms can be defined by three factors.
1. Atomic number
2. Atomic weight
3. Electrical charge

Nucleus
It is a central part of an atom, which contains protons and neutrons.
A proton is a positively charged particle, while the neutron has the same ‘mass’ as the proton , but has no charge.

Therefore the nucleus of an atom is positively charged. The sum of protons and neutrons decides the entire weight of an atom.
Because, the particle in the extra nucleus (i.e.,electrons) have negligible weight as compared to protons and neutrons.

Extra Nucleus :
It is the outer part of an atom which contains electrons only.
An electron is a negatively charged particle having negligible mass. The charge of an electron is equal but opposite to that of a proton. Also the number of electrons are equal to the number of protons in an atom under ordinary conditions.

Therefore an atom is neutral as a ‘whole’. The number of electrons or protons in an atom is called atomic number.

Atomic Number Normally at ordinary conditions the number of electrons in the extra nucleus (i.e, orbits) are equal to number of protons present in the nucleus. Therefore, an atom is neutral as a whole. The number of electrons or protons in an atom is called atomic number.

Atomic Weight
The sum of the protons and neutrons decides the entire weight of an atom and is called atomic weight.
The electrons are not taken for consideration because it is having negligible mass as compared to protons or neutrons.

The electrons present in the atom is root cause for the action of any type of conduction (say electricity, heat etc).The electrons in an atom revolve around the nucleus in different orbit or paths.
The number and arrangement of electrons in any orbit is determined by the following rules.

STRUCTURE OF ELEMENTS
We have seen all atoms are made up of protons, neutrons and electrons. The difference between types of elements is due to the different number and arrangement of these particles within their atoms. The structure of copper atom is different from carbon atom and hence the two elements have different properties.
The atomic structure can be easily drawn if we know the atomic weight and atomic number of an element.

Free Electrons
The valence electron of different material possesses different energies. The greater the energy of a valence electron, the lesser it is bound to the nucleus. In certain substance, particularly metals, the valence electron possess so much energy that they are very loosely attached to nucleus.
These loosely attached valence electron move at random within the material and are called free electrons.

The free electrons can be easily removed or detached by applying a small amount of external energy. As a matter of fact, these free electrons which determine the electrical conductivity of the material. On the basis of free electron concept, the conductors, insulators and semiconductors can be defined as under:

1. A conductor is a substance which has a large number of free electrons. When potential difference is applied across a conductor, the free electron move towards positive terminal of supply constituting electric current.

2. An insulator is a substance which has practically no free electrons at ordinary temperature. Therefore an insulator does not conduct current under the influence of potential difference.

3.A semiconductor is a substance which has very few free electrons at room temperature. Under the influence of potential difference, a semi-conductor practically conducts no current.

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