What are N-type and P-type Semi Conductors
All of us know the importance of the semi conductor technology in our world today. From the simplest of amplifiers to the most complex super computer chips, the semi conductors remain the basic building blocks. And two of the widely used semi-conductor materials are Silicon and Germanium. But in their pure or intrinsic form, these possess almost negligible
So in the crystal growth stage of these materials, some impurities are added to greatly enhance their electrical conductivity. The process is known as doping and the semi conductor material so form is known as an extrinsic semi conductor. This extrinsic semi conductor can be either of N-type or P-type depending upon the nature of the impurity that is added.
N-type semi conductors are formed by addition of pentavalent impurities such as Arsenic, Antimony, Phosphorus or Bismuth. These impurities have five electrons in the outer most shell and when they replace a Silicon or a Germanium atom in a lattice, four of these electrons are used up in the process of forming covalent bonds with the neighboring atoms while the fifth electrons becomes nearly free from the effect of the parent nucleus and is thus added to the conduction band of the material, thereby enhancing the conductivity. An addition of a small amount of impurities can enhance this conductivity by a large amount as it greatly increases the population of electrons in the conduction band. The electrons thus become the majority carriers of electric current and the material is known as an N-type Semi conductor.
Similarly P-typed semi-conductors are formed by addition of trivalent impurities such as Boron, Gallium, and Indium etc. These impurities have three electrons in the outer most shell and thus are able to form covalent bonds with only three of the four neighboring atoms in the Silicon crystal. This leads to addition of holes in the valence band of the material that enhances the conductivity. The holes become the majority carriers of electric current here and consequently the material is known as P-type Semi Conductor.
It is important to remember that both these materials are electrically neutral as whole because the addition of holes or electrons is always countered by the charge on the parent nuclei of the impurity atoms. Now it is these p-type and n-type semi conductors that are combined to form extremely important electronic devices like BJT’s, FET’s, Diodes, UJT’s etc. Without the advent of these devices, the picture of our science and technology would have been completely different today.