INTRINSIC AND EXTRINSIC SEMICONDUCTORS

Classification of

Intrinsic and Extrinsic semiconductors

semiconductors are the substances which do not conduct current at room temperature. conduction takes place through a semiconductor when the temperature of the semiconductor is slightly increased.

germanium and silicon are the examples of semiconductors.

semiconductors are classified into two types.

1. pure semiconductor ( intrinsic semiconductor)

2.impure semiconductor(extrinsic semiconductor)

Intrinsic semiconductors

1. An intrinsic semiconductor is extremely pure semiconductor.

2.It consists purely the atoms of semiconductor only.

3.The examples are pure germanium and silicon.

4.At room temperature intrinsic semiconductor does not contain free electrons and holes.

The valency of germanium or silicon is 4.

Hence every atom of germanium or silicon forms. four covalent bonds with 4 neighbor atoms.

at room temperature all 4 bonds are completely filled.

5.Free electrons are released when temperature of the substance is increased.

6.The number of free electrons is equal to number of holes.

7.When the pure semiconductor is connected to external battery, the conduction is due to electrons as well as holes.

8.The conduction is very low through intrinsic semiconductor.

Covalent bonds in pure semiconductor

Extrinsic semiconductors

1. An extrinsic semiconductor is formed by adding impurities to a pure semiconductor by doping process.

2.There are two types:1.P- type semiconductor and 2. N- type semiconductor.

3.P- type semiconductor is formed by doping a pure semiconductor with trivalent atoms(3rd group atoms).

4.N- type semiconductor is formed by doping a pure semiconductor with pentavalent atoms (5th group)

5.Holes are majority charge carriers in P-type semiconductor. Conduction is due to motion of holes.

6.Electrons are majority charge carriers in N-type semiconductor. Conduction is due to motion of free electrons.

p - type semiconductor

n- type semiconductor

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