What are n-type and p-type semiconductors?

Explanation

Semiconductors are of two types. They are 1) Intrinsic semiconductors 2) Extrinsic semiconductors.
1) Intrinsic semiconductors: In this of semiconductors the electrical conductivity is due to the jump of electrons to the conduction band. Ex: Silicon and Germanium.
Extrinsic semiconductors : This conductivity is due to the presence of impurities like silicon and germanium. This process is called doping. Doping can be done, with an impurity which is electron rich or electron deficient. Extrinsic semiconductors are of two types.
n-type semiconductors : When silicon is doped with small amounts of V group elements such as P, As or Sb, out of the five valence electrons of these elements four will form four covalent bonds with four valence electrons of silicon. The excess electron left on the atoms of V group element delocalize and contribute to electrical conduction. So conductivity increases. Here the increase in conductivity is due to the negatively charged electron. So this type of semiconductors are called n-type semiconductors.
p - type semiconductors : Electrical conductivity of silicon and germanium can also be increased by doping with III A group elements such as B, Al or Ga. The atoms of these elements have only three valence electrons and can form three covalent bonds with silicon or germanium. The place where the fourth valence electron is missing is called electron hole or electron vacancy. An electron from a neighbouring atom can come and fill the electron hole creating a new hole at its original position. Thus the holes can move through out the crystal like a positive charge giving rise to electrical conductivity. This type of semiconductors are called p - type semiconductors.