How are P and N type semiconductors formed?

Answer 1

FORMATION OF P-TYPE SEMI CONDUCTOR A P - type semiconductor is formed when a small amount of trivalent impurity is added to pure Germenium or silicon atom crystal. The addition of trivalent impurity produces a large no. of holes to the host crystals. To explain the formation of P - type semiconductor, let usintroduce a trivalent impurity into the lattice of a pure silicon crystal. The trivalent atom has 3 valanceelectrons and form covalent bonds with neighbouring atoms. The 4th bond is incomplete . the trivalent atom then attracts an electron from an adjacent atom there bycompleting the 4th bond and forming a hole in the adjacent atom. Since a trivalent impurity atom provides 1 hole, an enormous increase occurs in the number of holes. The impure crystals so obtained is called P - type semiconductor where P represents the positive charge on hole. Thus the majority carrier in a P - type semiconductor are holes. Freeelectrons are also present in the P - type semiconductor. These are thermally generated and since they relatively few, they are called minority carriers. The trivalent impurity atoms are called acceptors because each accepts an electron when the atom is introduced into the host crystal.

FORMATION OF N TYPE SEMI CONDUCTOR

An N - type semiconductor is formed when a small amount of pentavalent impurity is added to a pure Germenium or Silicon crystal. The addition of pentavalent impurity produces a large no. of free electrons in the host crystal.

To explain the formation of N - type semiconductor, let us introduce a pentavalent impurity atom into the lattice of pure silicon crystal. The pentavalent atom has 5 valance electrons, but only 4 form covalent bonds with the neighbouring atoms. The 5th electron finds no place in the covalent bonding so becomes free. Since an impurity atom provides one free electron, an enormous increase occurs in the no. of free electrons. The impure semiconductor so obtained is then called as N - type semiconductor where N represents negative charge on an electron. Thus the majority carrier in N - type semiconductor are free electrons. Holes are also present in the N - type semiconductor. These are thermally generated and since they are relatively few, they are called minority carrier.

The pentavalent impurity atom are called donour because each donate a free electron to the host crystal.