Effects of doping in diodes

Pure Silicon or Germanium are rarely used as semiconductors. Practically usable semiconductors must have controlled quantity of impurities added to them. Addition of impurity will change the conductor ability and it acts as a semiconductor. The process of adding an impurity to an intrinsic or pure material is called doping and the impurity is called a dopant. After doping, an intrinsic material becomes an extrinsic material. Practically only after doping these materials become usable

Effect of Doping on N-type Material

The effect of doping on an N-type material is as follows −

On addition of Arsenic to pure Silicon, the crystal becomes an N-type material.

Arsenic atom has additional electrons or negative charges that do not take part in the process of covalent bonding.

These impurities give up or donate, one electron to the crystal and they are referred to as donor impurities.

An N-type material has extra or free electrons than an intrinsic material.

An N-type material is not negatively charged. Actually all of its atoms are all electrically neutral.

These extra electrons do not take part in the covalent bonding process. They are free to move about through the crystal structure.

An N-type extrinsic silicon crystal will go into conduction with only 0.005eV of energy applied

Effect of Doping on P-type Material

The effect of doping on a P-type material is as follows −

When Indium (In) or Gallium (Ga) is added to pure silicon, a P-type material is formed.

This type of dopant material has three valence electrons. They are eagerly looking for a fourth electron.

In P type material, each hole can be filled with an electron. To fill this hole area, very less energy is required by electrons from the neighboring covalent bonded groups.

Silicon is typically doped with doping material in the range of 1 to 106. This means that P material will have much more holes than the electron-hole pairs of pure silicon.

At room temperature, there is a very determined characteristic difference in the electrical conductivity of this material.