Describe the two main types of semiconductors.

Explanation

Substances whose conductance lies between that of metals (conductors) and insulators are called semiconductors.
(i) n-Type semiconductors : Silicon that has been doped with a Group-15 element such as P, As, Sb, Bi is called an n-type semiconductor, .n. standing for negative since electrons are responsible for the semiconducting behaviour.

(ii) p-Type semiconductors : Droping a silicon crystal with a Group-13 element, such as B, Al, Ga or In produces a silicon crystal structure in which an occasional dopant atom is present with only three valence electrons. The place where the fourth valence electron is missing is called an electron vacancy or a hole. Such holes can move through the crystal like a positive charge giving rise to electrical conductivity. Direction of motion of the holes in an electric field is opposite to that of the electrons. Group-13 doped crystals of silicon are called a p-type semiconductors since holes (positive in charge) appear to be responsible for the semiconducting properties.
Use of n-Type semiconductors. Various combinations of n-type and p-type semiconductors are used to make electronic components, for example a diode is a combination of p-and n-semiconductor and is used as a rectifier. Transistors which are npn .Sandwich. semiconductor are used to detect or amplify radio or audio signals. The soalr cell is essentially an efficicent photo diode used for converting radiant (light) energy into electric energy.