Question

Question 6. Part (i).
6. (i) Classify each of the following as being either a p-type or n-type semiconductor. Give reason.
(a) Si doped with In
(b) Si doped with P.

Answer 1

Dear Student,
A)Silicon has structured with in which silicon is surrounded tetrahedrally by four other atoms .The add atom has three valance electrons and therefore does not have enough electrons to form bonds to its four silicon neighbours .The vacancies in the valance band can be thought of as positive holes in a filled band .
Because the charge carrier can be regarded as the positive holes so silicon doped with group 3 A element is called p-type semiconductor.
B) Silicon crystal doped with traces of P,P atom has five valance electrons ,and silicon has four .To be accommodated into silicon structure ,each P atom must give up one electron because they give up electrons ,the P atoms in doped semiconductor are called donor atoms.
The conduction band and donor levels are close to each other and hence thermal energy alone is enough to cause extra valance electron of P atom to be lost to conduction band In this process ,the P atom become immobile positive ion P⁺electrical conductivity in the semiconductor involves the primarily the movement of electrons in the conduction band with majority of electrons coming from donor atoms.
Regards