Main Difference

The main difference between the Intrinsic Semiconductor and Extrinsic Semiconductor is that the Intrinsic semiconductor is the pure type of semiconductor, whereas Extrinsic Semiconductor includes impurities in it.

Intrinsic Semiconductor vs. Extrinsic Semiconductor

An intrinsic semiconductor is recognized as the purest type of the semiconductor. On the flip side, when impurities in small quantities are added in the semiconductor, then the semiconductor is known as an extrinsic semiconductor; due to the addition of impurities in extrinsic semiconductors, they have better conductivity than intrinsic semiconductors.

The intrinsic semiconductors can also be recognized as i-type semiconductor or undoped semiconductor. On the other side, the extrinsic semiconductor is also recognized as a doped semiconductor. An intrinsic semiconductor is not divided into any type, whereas; extrinsic semiconductors are further divided into p-type semiconductors and n-type semiconductors.

In intrinsic semiconductors, electrons present in the conduction band and holes present in the valence band are equal in number. On the other hand, electrons and holes are not equal in number in extrinsic semiconductors; electrons are in the majority in an n-type semiconductor, and holes are in the majority in a p-type semiconductor.

In intrinsic semiconductors, the center of the forbidden energy gap has the Fermi energy level. On the flip side, in the n-type extrinsic semiconductor, the Fermi level is present near the bottom of the conduction band, whereas it is near the top of the valence base in the p-type extrinsic semiconductor.

In intrinsic semiconductors, there is a small bandgap between the valance band and conduction. On the other side, the extrinsic semiconductor has a higher energy gap then intrinsic semiconductor. The conduction of intrinsic semiconductors depends upon temperature, whereas the conduction of extrinsic semiconductors depends on the temperature and concentration of doped impurity.

The examples of intrinsic semiconductors are Si and Ge etc. On the flip side, the examples of extrinsic semiconductors are GaAs, GaP, etc.

Comparison Chart

What is the Intrinsic Semiconductor?

The word ‘intrinsic’ stands for ‘pure.’ So, the intrinsic semiconductor is a pure semiconductor without any dopant element or impurity present in it. This type of semiconductor is also recognized as an i-type semiconductor or undoped semiconductor. That is why the amount of charge carriers is based on the properties of the material but not on the number of impurities.

In intrinsic semiconductors, electrons present in the conduction band and holes present in the valence band are equal in number. Here, holes are denoted by p, and electrons are denoted by n, so, in an intrinsic semiconductor, n = p. In this type of semiconductors, electric-powered conductivity depends on the crystallographic flaws or even electron excitation.

In intrinsic semiconductors, the center of the forbidden energy gap shows the Fermi energy level. There is a small bandgap between the valance band and conduction. At low temperatures, the electrons are not much excited to reach a higher energy state. So, the electrons remain in the valence band without showing any movement towards the conduction band. With the increase in temperature, electrons get excited and reach the conduction band from the valance band that results in the flow of current.

In the periodic table, the elements of group IV form intrinsic semiconductors. However, germanium and silicon play their role as intrinsic semiconductors as they require only a small amount of energy to break the covalent bond. Both silicon and germanium have diamond-like structures. They both have four valence electrons. Each atom bounds one of its valence electrons by its neighboring four atoms in the crystalline form. These pairs of shared electrons form a valance bond or covalent bond.

With the increase in temperature, the valence electrons obtain more energy. Due to this energy, they break away the covalent bond and cause an increase in the conductivity of the element. Here, only a few atoms get ionized by the thermal energy. This ionization causes the formation of a vacancy in the bond.

Due to the thermal energy, when an electron with –q charge, gets excited, it breaks itself from the bond that causes there a vacancy with +q charge. This vacancy with a positive electronic charge acts as a hole. These holes also act like free particles but with a positive charge. In intrinsic or undoped semiconductors, the free electrons are equal in number to the holes, and this phenomenon is known as intrinsic carrier concentration.

What is the Extrinsic Semiconductor?

An extrinsic semiconductor is a type of semiconductor that has been doped with any trace element or impurities during its manufacturing. The elements added in it are known as doping agents, and this process is known as a doping agent. So, the extrinsic semiconductor is also called as the doped semiconductor. Such semiconductors have better conductivity due to the addition of impurities in them. So, the number of charge carriers is based on the properties exhibit by the material and the impurities added in it.

The extrinsic semiconductor shows a higher energy gap. Its conduction is based on the temperature and concentration of doped impurity. Moreover, electrons and holes are not equal in number in extrinsic semiconductors.

While doping a material, a point should be kept in mind that the amount of impurity mixed in the material should not affect the lattice structure of the Semiconductor. To get this point, the size of the semiconductor atoms and the dopant should be the same. For example, the crystals of the silicon and germanium are mixed with trivalent ( 3 valencies) and the pentavalent (5 valencies) because they have the same crystal size.

Types

• n-type Semiconductors: These types of semiconductors are obtained when pure semiconductors are mixed with pentavalent (valency 5) elements. When Silicon is mixed with pentavalent elements, four of its electrons will get attach to four neighboring Silicon atoms by forming a bond with them. But, the fifth electron will remain loosely attached to the parent atom. So, to set this electron free, the required ionization energy is very low. That is why this loosely attached electron may travel in the lattice even at room temperature. For example, the ionization energy needed for silicon at room temperature is about 1.1 eV. But, after the addition of a pentavalent impurity in it, this energy will reduce to 0.05 eV.
• P-type Semiconductor: A p-type semiconductor is formed when pure semiconductors are mixed with trivalent (valency 3) doping agents. For example, with the addition of a trivalent element in a silicon atom, three of its electrons will form a bond with three of its neighboring Silicon atoms. But, there is no electron free to form a bond with the fourth Silicon atom. This process causes the formation of a vacancy or a hole between the fourth silicon atom and the trivalent. So, an electron from the outer orbit of the neighboring atom will jump off to fill this hole. This jump of the electron will create a hole at the site of its presence. In other words, for conduction, a hole is available.

Key Differences

Conclusion

The above discussion summarizes that intrinsic semiconductor is a type of pure semiconductor without any impurity added in it, e.g., silicon or germanium, etc. On the other side, the extrinsic semiconductor is a type of impure semiconductor with the doping agents or impurities added in it, e.g., GaP or GaAs, etc.

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