# NEET Chemistry The Solid State Questions Solved

BOARD

What is a semiconductor? Describe the two main types of semiconductors and contrast their conduction mechanism.

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 4th 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 5th e- conducts electricity.

Difficulty Level:

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