Question

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?

Answer 1

(i) Antimony and phosphorus.

(ii) By adding a pentavalent impurity to a pure Ge or Si, the number of free electrons increases and thus the conductivity increases.

The impure Ge or Si crystal is called n type semiconductor..

The process of adding impurity to an intrinsic semiconductor in a controlled manner is called doping and the impurity atom added are called dopants.

N type semiconductor :

When a pentavalent impurity atom is added to Ge or Si (tetravalent) crystal, it replaces it in the crystal lattice.

When a pentavalent impurity atom is added to Ge or Si (tetravalent) crystal, it replaces it in the crystal lattice. Thus by adding pentavalent impurity ,the number of free electrons.

When a pentavalent impurity atom is added to Ge or Si (tetravalent) crystal, it replaces it in the crystal lattice. Thus by adding pentavalent impurity ,the number of free electrons. The impurity atoms are called the donar atoms as they donate the negative charge carriers or electrons to the crystal.

When a pentavalent impurity atom is added to Ge or Si (tetravalent) crystal, it replaces it in the crystal lattice. Thus by adding pentavalent impurity ,the number of free electrons. The impurity atoms are called the donar atoms as they donate the negative charge carriers or electrons to the crystal. In N type semiconductor the electrons are the majority carriers and the holes are the minority carriers.

LAW OF MASS ACTION :

$n_{e}n_{h} = n_{i}^{2}$

where,

ne and nh were the hole concentration and ni is the intrinsic concentration.