All of you heard about semiconductor but you know what is semiconductor? How works semiconductors? what is semiconductor doping? 

Semiconductor is most useful for our life without semiconductor life is not possible. In emerging technology semiconductor plays a important role for technology. 



What is semiconductor - 

A semi- conductor's material is one whose electrical properties lie in between those of insulators and good conductors. Examples are Germanium and Silicon.

Germanium - 

Germanium has become the model substance among the semiconductors; the main reason being that it can be purified relatively well and crystallised easily. Germanium is an earth element and was discovered in 1886.  The atomic number of silicon is 32. 

Silicon - 

Silicon is an element in most of the common rocks. Actually, sand is silicon dioxide. The silicon compounds are chemically reduced to silicon which is 100% pure for use as a semiconductor. The atomic number of silicon is 14. 

Classification of semiconductors - 

The semiconductors are two types:

1. Intrinsic Semiconductor 

2. Extrinsic Semiconductor

1. Intrinsic Semiconductors: 

A pure semiconductor (free from any impurity) is called an 'intrinsic semiconductor'. Thus, pure germanium and pure silicon in their natural form are intrinsic semiconductors, and their electrical conductivity is "intrinsic' conductivity.

2. Extrinsic Semiconductors: 

If a small amount of some pentavalent or trivalent impurity be introduced into a pure semiconductor, its conductivity increases appreciably. Such impure semiconductors are called 'extrinsic' or 'impurity' semiconductors, and the resulting conductivity is called 'extrinsic' conductivity.

The process of introducing the impurity is known as 'doping'. Hence, the impurity,  semiconductors are also known as 'doped' semiconductors. The n-type and p-type semiconductors are doped (extrinsic) semiconductors.




Classification of extrinsic semiconductors - 

Extrinsic semiconductors are classified into two parts:

(i) n-type semiconductor 

(ii) p-type semiconductor

(i) n-type semi-conductor: 

If a small amount of pentavalent impurity (having five valence electrons) is added to a pure semi-conductor, it is known as N-type semi conductor.

Mechanism of current flow: 

Typical examples of pentavalent impurities are arsenic (As, Z=33) and antimony (Sb. Z= 51). In the crystal, they will be surrounded by the atoms of the semiconductor material. Four (out of five) valence electrons of impurity atom form covalent bonds with the four valence electrons of the neighboring Ge atoms. The fifth valence electron of impurity (say, As) finds no place in covalent bonds and remains free to move randomly in the crystal lattice. Thus each impurity atom donates a free electron to the semi-conductor. Hence, the impurity is called the donor impurity. The semi-conductor containing semiconductor crystal. Ge donor type impurity is called N-type semi-conductor because it has negative charge carriers (electrons).

(ii) P-type semi-conductors: 

If a small amount of trivalent impurity (having three valence electrons) is added to a pure semi-conductor, it is known as P-type semi-conductor.

Mechanism of current flow: 

Typical examples of trivalent impurities are gallium (Ga, atomic number 31) and indium (In, atomic nuber 31) germanium crystal, three valence electrons of impurity atoms form covalent bonds with three valence electrons from three neighboring atoms. There is a deficiency of independent atomic number 49). When a small amount of such impurity (say, In) is added to one electron to complete the fourth bond. This electron deficiency is called the hole and it behaves like a positively.

Conclusion - 

I hope you will know everything about that what is semiconductor? How works semiconductors? what is semiconductor doping? So if you have any question you can ask me in comment.