The semiconductor materials are classified as intrinsic and extrinsic semiconductors. The intrinsic semiconductors are not classified further while extrinsic semiconductors can be further classified as n-type or p-type semiconductors on the basis of the nature of doping. If the impurity added to the intrinsic semiconductor is of group V then the semiconductor thus formed is known as an n-type extrinsic semiconductor and will have an excess of electrons.
If the impurity added to the intrinsic semiconductor is from group III then the semiconductor obtained after doping is known as a p-type semiconductor since there will be an excess of holes. The majority of charge carriers in P-type semiconductors are holes while in the N-type semiconductors are electrons.
The differences between the two (p-type and n-type semiconductor) are explained on the basis of a number of factors like- doping element, nature of doping element, the density of electrons and holes, energy level and Fermi level, the majority, and minority carriers in the p-type and n-type semiconductor, the direction of movement of majority carriers, etc.
Difference between P type and N type Semiconductor – Table
Now let’s see the difference between p-type and n-type semiconductor with the help of a table.
| P-type semiconductor | N-type semiconductor |
| P-type semiconductors are formed due to doping of elements of group III i.e. Boron, Aluminium, Thallium, etc. | N-type semiconductors are formed due to doping of elements of group V i.e. Nitrogen, Phosphorus, Arsenic, Antimony, Bismuth, etc. |
| Holes are the majority carriers in P-type semiconductors. | Electrons are the majority carriers in n-type semiconductors. |
| Electrons are the minority carriers in P-type semiconductors. | Holes are minority carriers in N-type semiconductors. |
| The fermi energy levels of these materials lie between the impurity energy level and the valence band. | The Fermi levels of these materials lie between the impurity energy level and the conduction band. |
| The movement of majority carriers is from higher potential to lower potential. | The movement of majority carriers is from lower potential to higher potential. |
| In P-type semiconductors, hole density is greater than the electron density. Nh > Ne |
Electron density is much greater than the hole density for the n-type semiconductors. Ne > Nh |
What are N-type semiconductors?
It is a type of extrinsic semiconductor in which the doping is from the elements of group V. In intrinsic semiconductors, the elements from group V are added to increase or enhance their conductivity. The majority carriers in N-type semiconductors are electrons and the minority carriers are holes.
The 4 electrons of the group V element make covalent bonds with the four neighbouring atoms of group IV (silicon) and one electron of the pentavalent atom is left free. This extra free electron moves freely in the structure and is responsible for the flow of current. Due to the releasing of electron pentavalent atom is known as donor atom.
The impurity added to the intrinsic semiconductors provides extra electrons and the atoms which provide extra electrons are known as donor atoms. In N-type semiconductors, the electron density is much greater than the hole density. In N-type semiconductors, the donor energy level is close to the conduction band and away from the valence band. The majority charge carriers move from the lower potential to the higher potential.
In N-type semiconductors, the Fermi level lies between the donor energy level and the conduction band. N-type semiconductors are also known as pentavalent semiconductors.
What are P-type semiconductors?
The type of extrinsic semiconductor in which the impurity is added from the elements of group III. P-type semiconductors are formed when the elements of group III are added to the intrinsic semiconductors and this is done to increase or enhance the conductivity of intrinsic semiconductors. In P-type semiconductors the majority carriers are holes and the minority carriers are electrons.
The impurity added to the P-type semiconductors creates vacancy of electrons (holes) and the added atoms are known as acceptor atoms. In P-type semiconductors, the hole density is greater than the electron density. The energy level of the acceptor atoms is close to the valence band and away from the conduction band. The Fermi level of the P-type semiconductors lies between the acceptor energy level and the valence band.
In P-type semiconductors, the majority charge carriers move from higher potential to low potential. The impurity added in this type of semiconductor has the ability to take an electron hence they are known as acceptor atoms.
Conclusion
We have concluded that both n-type and p-type semiconductors are types of extrinsic conductors. P-type semiconductors have an excess of holes while N-type semiconductors have an excess of electrons. The majority of charge carriers in P-type semiconductors are holes while in N-type semiconductors are electrons.
In p-type doping, boron or gallium is used as the dopant while in n-type doping arsenic or phosphorus are added in small quantities as a dopant to the silicon.
Author
Deepak Yadav
Aligarh Muslim University, Aligarh
