What is Doping?
As we discussed, the conductivity of intrinsic semiconductors is very low, so to increase the conductivity of the semiconductor we add some impurity atoms to the semiconductor, which are known as dopants, and the process is known as doping.
Conditions for doping:
- The doping ratio must be equal to 1 ppm (1 part per million), that means for every 106 pure atoms there exists 1 impure atom, i.e. 106: 1
- The size of a dopant / impure atom must be equal to the size of a pure atom, to maintain the crystal structure.
b) Extrinsic Semiconductor
A semiconductor in which the number of electrons and holes are unequal is known as an extrinsic semiconductor. An extrinsic semiconductor is formed by adding the impure atom or dopant to the pure semiconductor. It is also known as an impure and doped semiconductor.
Extrinsic / Impure / Doped semiconductor = Instrinsic / Pure semiconductor + Dopants
In extrinsic semiconductors, doping is done to increase the conductivity of semiconductors, so we can use them to create some practical devices. If we consider Silicon or Germanium as our semiconductor, there are two different groups of elements that are suitable for use as dopants, Group 13 (BORON FAMILY) & Group 15 ( NITROGEN FAMILY) based on the conditions of doping.
Extrinsic Semiconductor
As we all know, based on conductivity, we divide the material into three categories: Conductor, Semiconductor, and Insulator. In which the conductivity of the conductor is highest, insulators have the lowest conductivity, and semiconductors have intermediate conductivity. The reason behind this is the number of free electrons present in the crystal of each material. If we talk about the conductivity of semiconductors, two different types of semiconductors are classified based on the number of electrons and holes present in the crystal: Intrinsic and Extrinsic semiconductors. In this article, we will discuss these semiconductors, especially extrinsic semiconductors, their properties, formation, needs, and various applications.