Describe the two main types of semiconductors and contrast their conduction mechanism.

Doping : Conductivity of semi conductors is too low to be of practical use. Their conductivity
is increased by adding an appropriate amount of suitable impurity. This process is called ‘doping’.
Semi conductors : Substances whose conductance lies in between that of conductors & Insulators are called semiconductors.
Semiconductors are two types.
1) Intrinsic semi conductors: Pure form of semiconductors are known as intrinsic semiconductors
Ex: pure Si & Ge
2) Extrinsic semi conductors: Impure semi conductors formed by doping impurities to
intrinsic semiconductors called as extrinsic semi conductors. These are two types.
a) n-type semi conductors: These semi conductors formed by doping VA (N, P, As)
group elements to pure Si or Ge. Conductivity increased due to presence of extra negatively charged electron.

b) P-type semi conductors: These semi conductors formed by doping IIIA (B, Al,
Ga) group elements to pure Si or Ge. Conductivity increased due to presence of positive charged hole.