NEET Chemistry The Solid State Questions Solved

Semiconductor : The solids which have intermediate conductivities between metals and non-metals i.e. between 10^-6 to 10⁴ $\mathrm{\pi }$^-1 m^-1 are called semiconductors.

Example : Germanium and silicon.

Main types of semiconductors are of two types :

(i) Intrinsic semiconductor : These are insulators at room temperature and become semiconductors when temperature is raised

(ii) Extrinsic semiconductor : p-type semiconductor

                                          n-type semiconductor

These are formed by doping impurity of lower or higher group.

These are subdivided into two types :

$\to$p-type semiconductors : When a silicon crystal is doped with atoms of group-13 elements like B, Al, Ga etc., the atom forms only 3 covalent bonds with the Si atom and 4^th missing electron creates a hole which conducts electricity.

$\to$n-type semiconductor : When a silicon crystal is doped with atoms of group-15 elements like P, As etc., then only four of the five valence electrons of each impurity atom participate in 4 covalent bond formation and 5^th e^- conducts electricity.