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
|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.
Key Differences Between Intrinsic and Extrinsic Semiconductor
- The factor that generates a key difference between intrinsic and extrinsic semiconductor is that the intrinsic semiconductors are said to be pure and thus no impurity concentration is present in it. As against, extrinsic semiconductors are said to be impure as an impurity is doped in order to form it.
- Due to its pure form, intrinsic semiconductors possess low conductivity. While extrinsic semiconductors exhibit comparatively better conductivity than the intrinsic semiconductor.
- There is an almost equal concentration of electrons and holes are present in case of an intrinsic semiconductor. On the contrary, the concentration of electron and holes depends on the type of extrinsic semiconductor.
- The conductivity of an intrinsic semiconductor truly relies on the temperature. On the contrary, the conductivity of the extrinsic semiconductor depends on temperature as well as impurity concentration.
- Intrinsic semiconductor does not hold any further classification whereas extrinsic semiconductors are classified as p and n-type semiconductors.
- Silicon or Germanium are examples of intrinsic semiconductors. Whereas doping arsenide or phosphorus like elements in pure semiconductor forms extrinsic semiconductor like GaAs or GaP.
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.