‘P’ AND ‘N’ TYPE MATERIALS

P-type and n-type germanium or silicon is used in the construction of transistors. Now question arise that what is transistors?  For that we have to first understand concept of P-type and N-type materials. These both types of materials are made by adding impurities of certain elements to the pure germanium and silicon. The act of adding an element as an impurity to the germanium or silicon is called doping.

(a)    P- Type Material :

When a trivalent element such as indium or gallium is added to tetravalent germanium or silicon as an impurity then a deficit of an electron is produced for each indium atom. The deficit of electron is termed as ‘hole’. The ‘holes’ producing impurity atoms are called acceptor atoms and the material consisting of acceptor atoms is called p-type material.

(b)    N- Type Material :

When a pentavalent element such as arsenic or antimony is added to tetravalent germanium or silicon as an impurity then a surplus electron is produced by each arsenic atom. The fifth electron of the impurity atom does not find any place in the covalent structure of the semi-conductor and it starts to wander as a free electron in the crystal. ‘Free electrons’ producing impurity atoms are called donor atoms and the material consisting of donor atoms is called N-type, material.

P and N type material are also known as extrinsic materials.