A pure semiconductor germanium or silicon, free of every impurity is called intrinsic semiconductor. A room temperature, a pure semiconductor has a very small number of current carriers (electrons and holes). Hence, its conductivity is low.
When the impurity atoms of valence five or three are doped in a pure semiconductor, we get repectively n-type ot p-type extrinsic semiconductor. In case of a doped semiconductor. `n_(e)n_(h)=n_(i)^(2)`,
where `n_(e)` and `n_(h)` are the number density of electrons and holes respectively and `n_(i)` is the number density of intrinsic charge carriers in a pure semiconductor. The conductivity of extrinsic semiconductor is much higher than that of intrinsic semiconductor.
(i) Name two materials to be doped in pure semiconductor of silicon to get p-type semiconductor n-type semiconductor.
(ii) What do you learn from the above study?

Explanation

(i) The doping of pure silicon with boron or aluminium will give us p-type semiconductor
The doping of pure silicon with arsenic or phosphorous will give us n-type semiconductor.
(ii) From the above study, we find that to get better output current, pure semiconductor has to be doped with suitable (impurity) atoms. Similarly, in day to day life, the appearence of right of person (leaders) in socity can improve their lot.