What is P-Type and N-Type Semiconductor?

Published by Nilofar Pathan on 25/05/202325/05/2023

Introduction to Semiconductor

The type of materials whose conductivity is greater than insulators but less than conductors are known as semiconductor materials.

In other words, a material is said to be a semiconductor, if it has 4 electrons in its outermost shell. The Semiconductor materials are broadly classified into two categories Intrinsic semiconductors and Extrinsic semiconductors.

In this article, we discuss the Extrinsic semiconductor, and we will compare the P-type and N-type semiconductors by considering various factors such as type of impurity added, nature of doping, majority charge carriers, the density of charge carriers, fermi level, etc.

But, before going into the actual differentiation of P-type and N-type semiconductor, we will define both types of semiconductors.

Extrinsic semiconductors are classified into two types −

• P-Types Semiconductor
• N-Type Semiconductor

The semiconductor itself is not an invention but many inventions are semiconductor devices. The discovery of semiconductor materials allowed for incredible and vastly significant advancements in the electronics industry.

Semiconductors were vital for the miniaturization of computers and computer parts and for the manufacturing of electronic parts such as diodes, transistors, and many other devices.

Streamlined Features of Semiconductors

• Semiconductors are like insulators at Zero Kelvin. But when the temperature is increased, they work as conductors.
• Due to their unique electrical properties, semiconductors can be modified through doping to make semiconductor devices suitable for energy conversion, switches, and amplifiers.
• They offer lesser power losses.
• They are smaller sized and possess less weight.
• Their resistivity is higher than conductors but lesser than insulators.
• The resistance of a semiconductor material decreases with the increase in temperature and inversely increases with a decrease in temperature.

These are some features of the semiconductors now we discuss P-Type Semiconductors and N-Type Semiconductors.

What is P-Type Semiconductor?

The P-type Semiconductor is formed when trivalent (having three valence electrons) impurities such as Gallium and Indium is added to a pure semiconductor in small amount, and as a result, many holes are created in it. These p-type-producing impurities are known as Acceptors because each atom of them creates one hole which can accept one bonded electron.

A positive charge hole is created when the three valence electrons of the impurity bond with three of the four valence electrons of the semiconductor and having one electron short, the covalent bond cannot be completed, hence the missing electron is known as a hole.

An extremely small amount of impurity has many atoms; therefore, it translates to millions of holes – which are the positive charge carriers – in the semiconductor. Hence, it is called a p-type semiconductor where ‘p’ stands for positive.

What is N-Type Semiconductor?

The N-type semiconductor is described as a type of extrinsic semiconductor doped with a pentavalent (having five valence electrons) impurity element. The pentavalent impurity or dopant elements are added to the N-type semiconductor to increase the number of electrons for conduction.

Examples of pentavalent impurities include Phosphorus, Arsenic, and Antimony. The impurity is added in very little quantity in the N-type semiconductor such that the crystal integrity of the base intrinsic semiconductor is not disturbed. The pentavalent impurity atom makes covalent bonds with four silicon atoms, leaving one electron not bonded with any silicon atom.

Each pentavalent impurity atom is said to donate one electron to the N-type semiconductor hence it is called a Donor impurity. Thus, there are more electrons than holes in the N-type semiconductor.

Because of the pentavalent impurity in an N-type semiconductor, several loosely bonded electrons populate the lattice structure. As a certain amount of voltage is applied, these electrons gain energy to break free and cross the forbidden gap, leaving the valence band to enter the conduction band.

This results in a very small number of holes being formed in the valence band. The Fermi level (the highest energy level an electron occupies at absolute zero temperature) is near the conduction band as more electrons enter the conduction band.

Difference between P-Type and N-Type Semiconductors

In determining the difference between p-type and n-type semiconductors, factors such as doping elements, the effect of doping elements, and the majority and minority carriers in both types are taken into consideration.

Additionally, the density of electrons and holes, energy level and Fermi level, the direction of movement of majority carriers, etc. are also accounted for in clarifying the disparity between p-type and n-type semiconductors. In this vein, therefore, the differences are outlined thus:

• As a main difference, in n-type semiconductors, the electrons have a negative charge, hence the name n-type. While in p-type, the effect of a positive charge is generated in the absence of an electron, hence the name p-type.
• In a p-type semiconductor, the III group element of the periodic table is added as a doping element, while in an n-type the doping element is the V group element.
•  In a p-type semiconductor, the majority carriers are holes, and the minority carriers are electrons. But in the n-type semiconductor, electrons are the majority carriers, and holes are the minority carriers.
• The electron density is much greater than the hole density in the n-type semiconductor represented as N_e >> N_h whereas, in the p-type semiconductor, the hole density is much greater than the electron density: N_h >> N_e.
• In an n-type semiconductor, the donor energy level is close to the conduction band and away from the valence band. While in the p-type semiconductor, the acceptor energy level is close to the valence band and away from the conduction band.
• The impurity added in a p-type semiconductor provides extra holes known as Acceptor atoms, whereas, in an n-type semiconductor, the impurity provides extra electrons called Donor atoms.
• The Fermi level of the n-type semiconductor rests between the donor energy level and the conduction band while that of the p-type semiconductor is between the acceptor energy level and the valence band.
• In the p-type semiconductor, many carriers move from higher to lower potential, in contrast to the n-type where many carriers move from lower to higher potential.
• Trivalent impurities such as Aluminium, Boron, Gallium, and Indium are added in the p-type semiconductor, whereas in the n-type semiconductor, Pentavalent impurities like Arsenic, Antimony, Phosphorus, and Bismuth are applied.

Conclusion

So, from the above discussion, we can conclude that a p-type semiconductor is abbreviated so because these are positive semiconductors due to the presence of extra holes. Whereas n-type semiconductors are termed negative semiconductors because of the presence of extra electrons.

Both P-type and N-type semiconductors are extrinsic semiconductors. However, the key difference between the two is that a P-type semiconductor is obtained by adding the trivalent impurity like aluminum in a pure semiconductor, while an N-type semiconductor is obtained by adding pentavalent impurity like phosphorous in a pure semiconductor.