Classification of semiconductor | intrinsic semiconductor

In this article, we will discuss about semiconductors and its types. Intrinsic semiconductor and extrinsic semiconductor.

What is a semiconductor ?

A semiconductor can be defined as aa material whose electrical conductivity lies between conductor and insulator. The electrical conductivity of conductor > semiconductor > insulator.

Some examples of semiconductor are silicon and germanium, they are also known as elemental semiconductor. They are mainly used to manufacture diodes, transistor and IC ( integrated circuit ). Semiconductors are widely used because they are compact, power efficient and cheap.

Based on the doping concentration or the level of purity. Semiconductor is classified into two types –

  1. Intrinsic or pure semiconductor
  2. Extrinsic or impure semiconductor

Intrinsic Semiconductor

Intrinsic semiconductor are chemically pure semiconductor. It can be defined as a semiconductor that is free from impurities. In this type of semiconductor the property of material determine the number of electrons and holes present in it ( instead of impurities ). In intrinsic semiconductor , the number of holes ( p ) and electrons ( n ) are equal p = n.

Intrinsic semiconductors are also known as i-type semiconductor or undoped semiconductor. They are usually made up of Silicon or germanium.

We know that both silicon and germanium has 4 electrons in their outermost ( valence ) shell. When the temperature of semiconductor is increased the electrons gains thermal energy and break out from their valence shell. In the process of ionization of atoms in a crystal lattice creates a vacancy in the bond between atoms. The position from which the electrons gets forced out has a hole which is equal to an effective positive charge. This hole is occupied by a free electron. As a result the latter vacant position becomes a hole and the former becomes a neutral position. In this way the hole is transferred from one position to another.

Mathematically, ni = p = n


ni = Intrinsic carrier concentration

p = Number of holes

n = Number of electrons

at 0 kelvin temperature, the intrinsic semiconductor behaves like an insulator. when the temperature is increased, the electrons gets excited and move to conduction band from valence band.

The conduction band gets partially occupied by these electrons, that leaves a equal number of holes in the valence band.

Extrinsic Semiconductor

An extrinsic semiconductor can be defined as semiconductor material in which doping material is predominantly used for conduction.

An extrinsic semiconductor is formed when chemical impurities ( like phosphorus, indium, boron, arsenic, etc )  are added to intrinsic or pure semiconductor. It is done to increase the current conduction capacity. Those impurity atoms contribute to conduction.

The current conduction capacity of extrinsic semiconductor is greater than intrinsic semiconductor.

The process of adding impurity to semiconductor is known as doping.

Extrinsic semiconductor is further classified into two types –

  1. N-type semiconductor
  2. P-type semiconductor

N Type Semiconductor

N-type semiconductor is formed when donor impurities ( pentavalent impurities ) are added to an intrinsic semiconductor.

Example of pentavalent impurities are phosphorus ( P ) and arsenic ( As ).

P Type Semiconductor

P-type semiconductor is formed when acceptor impurities ( trivalent impurities ) are added to an intrinsic semiconductor.

Example of trivalent impurities are Boron ( B ), Indium ( In ) and Gallium ( Ga ).


Akash Sharma

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