LESSON DEVELOPMENT

TYPES OF SEMI CONDUCTORS

There are two main types of semiconductors namely; intrinsic semiconductors and extrinsic semiconductors.

Doping of semi-conductors

Doping is the introduction of impurities in semi-conductors to alter their electronic properties. The impurities are called dopants. Doping heavily may increase their conductivity by a factor greater than a million. An intrinsic semi-conductor is one which is pure enough such that the impurities in it do not significantly affect its electrical behavior. Intrinsic semi-conductors increase their conductivity with increase in temperature unlike metals. An extrinsic semi-conductor is one which has been doped with impurities to modify its number and type of free charge carriers present.

There are two types of extrinsic semiconductors namely; n type and p type.

The n type semiconductor is formed by doping an intrinsic semiconductor with pentavalent atoms like phosphorous. A phosphorous atom has five electrons available for bonding four of which participate in forming covalent bonds with four neigbouring atoms of the pure semiconductor. The remaining electron is thus donated for electrical conductivity. The phosphorus atom is thus referred to as a donor atom or n type impurity. In p type semiconductor the electrons are the majority charge carriers.

The p type semiconductor is formed by doping an intrinsic semiconductor with trivalent atoms like boron. A boron atom has three electrons available for bonding. All the three electrons participate in forming covalent bonds with three neigbouring atoms of the pure semiconductor. There is one electron less to complete the bonding.

The vacant place due to the missing electron is called a hole. A hole is positively charged.  In p type holes become the majority charge carriers.

WATCH THE CLIP BELOW ON INTRINSIC & EXTRINSIC SEMICONDUCTORS.