What are extrinsic semiconductor ? Explain acceptor-type semi-conductors.

Explanation

Extrinsic semiconductors: The semiconductor obtained after adding impurities in an intrinsic semiconductor is known as an extrinsic semiconductor.
Acceptor type semiconductor or p-type semiconductor: When trivalent impurity is added to pure germanium or silicon crystal, we get p-type semiconductor. When trivalent impurity atom, say indium is added to pure germanium or silicon crystal, we get p-type semiconductor. When trivalent impurity atom, say indium is added to silicon crystal, it replaces one of the Si atom. This indium atom forms three convalent bonds with the neighbouring silicon atoms. The fourth bond remains incomplete which has a deficiency of one electron. This deficiency of an electron is called hole and behaves like a positively charged particle. This hole attracts the electrons from neighbouring covalent bond to fill itself. Now a new hole is created. In this way, large number of holes are formed by adding indium atoms is silicon crystal. This type of crystal having large number of holes or positive charge carriers is called p-type semiconductor. The majority charge carriers are holes and minority charge carriers are electrons in p-type semiconductor.