Difference Between Intrinsic and Extrinsic Semiconductor

Both intrinsic and extrinsic semiconductor is the 2 categorizations of semiconductor material. The difference between intrinsic and extrinsic semiconductor is that Intrinsic semiconductors are the pure form of semiconductor materials. Whereas extrinsic semiconductors are impure semiconductor formed by adding an impurity to a pure semiconductor.

No, any external impurity is doped in case of an intrinsic semiconductor while extrinsic semiconductors are formed by adding either trivalent or pentavalent impurities to the semiconductor material.

In the upcoming sections under this article, we will discuss some major differences between the two. But before moving for it let’s have a look at the contents that are to be discussed under this article.

Content: Intrinsic Vs Extrinsic Semiconductor

1. Comparison Chart
2. Definition
3. Key Differences
4. Conclusion

Comparison Chart

Parameter	Intrinsic Semiconductor	Extrinsic Semiconductor
Form of semiconductor	Pure form of semiconductor.	Impure form of semiconductor.
Conductivity	It exhibits poor conductivity.	It possesses comparatively better conductivity than intrinsic semiconductor.
Band gap	The band gap between conduction and valence band is small.	The energy gap is higher than intrinsic semiconductor.
Fermi level	It is present in the middle of forbidden energy gap.	The presence of fermi level varies according to the type of extrinsic semiconductor.
Dependency	The conduction relies on temperature.	The conduction depends on the concentration of doped impurity and temperature.
Carrier concentration	Equal amount of electron and holes are present in conduction and valence band.	The majority presence of electrons and holes depends on the type of extrinsic semiconductor.
Type	It is not further classified.	It is classified as p type and n type semiconductor.
Example	Si, Ge etc.	GaAs, GaP etc.

Definition of Intrinsic Semiconductor

An intrinsic semiconductor is formed from a highly pure semiconductor material thus also known as pure semiconductors. These are basically undoped semiconductors that do not have doped impurity in it.

At room temperature, intrinsic semiconductors exhibit almost negligible conductivity. As no any other type of element is present in its crystalline structure.

The group IV elements of the periodic table form an intrinsic semiconductor. However, mainly silicon and germanium are widely used. This is so because in their case only small energy is needed in order to break the covalent bond.

The figure below shows the crystalline structure of silicon:

The figure above clearly shows that silicon consists of 4 electrons in the valence shell. Here, 4 covalent bonds are formed between the electrons of the silicon atom.

When the temperature of the crystal is increased then the electrons in the covalent bond gain kinetic energy and after breaking the covalent bond it gets free.  Thus, the movement of free electrons generates current.

The rise in temperature somewhat increases the number for free electrons for conduction.

Definition of Extrinsic Semiconductor

Extrinsic Semiconductors are those that are the result of adding an impurity to a pure semiconductor. These are basically termed as an impure form of semiconductors.

The process by which certain amount of impurity is provided to a pure semiconductor is known as doping. So, we can say a pure semiconductor is doped to generate an extrinsic semiconductor.

These are highly conductive in nature. However, unlike intrinsic semiconductor, extrinsic semiconductors are of two types p-type and an n-type semiconductor.

It is noteworthy here that the classification of the extrinsic semiconductor depends on the type of element doped to the pure semiconductor.

The p-type semiconductors are formed by introducing group III elements or trivalent impurity into the pure semiconductor. These are also known as an acceptor impurity, as a trivalent impurity has only 3 electrons in the valence shell.

The n-type semiconductors are formed by the addition of group V elements or pentavalent impurity to a pure semiconductor. These are termed as donor impurity, as a pentavalent impurity holds 5 electrons in its valence shell.

The figure below represents the crystalline structure of n-type semiconductor:

Here, the above figure clearly shows that a pentavalent impurity is doped to a pure silicon crystal. In this case, 4 electrons of phosphorus are covalently bonded with the adjacent silicon atom. But, still, a free electron is left in this case.

Thus, the movement of these free electrons generates high conduction. Also, when the temperature is increased then it causes the covalent bond to get a breakdown. Hence generating more free electrons.

So, this is the reason why an n-type extrinsic semiconductor has electrons as the majority charge carrier.

Conclusion

So, from the above discussion, we can conclude that due to the absence of doped impurity an intrinsic semiconductor conducts somewhat very less than the extrinsic semiconductors.