Difference Between Intrinsic and Extrinsic Semiconductor

The main difference between intrinsic semiconductor and extrinsic semiconductor is that intrinsic semiconductor is the pure type of semiconductor while extrinsic semiconductor includes impurities.

Intrinsic Semiconductor vs. Extrinsic Semiconductor

An intrinsic semiconductor is recognized as the purest type of semiconductor. On the other hand, when impurities are added in small amounts in the semiconductor, the semiconductor is known as an extrinsic semiconductor; Due to the addition of impurities in extrinsic semiconductors, they have better conductivity than intrinsic semiconductors.

Intrinsic semiconductors can also be recognized as type io semiconductors or undoped semiconductors. On the other hand, the extrinsic semiconductor is also recognized as a doped semiconductor. An intrinsic semiconductor does not split into any type, whereas; Extrinsic semiconductors are further divided into p-type semiconductors and n-type semiconductors.

In intrinsic semiconductors, the electrons present in the conduction band and the 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 other hand, in the n-type extrinsic semiconductor, the Fermi level is present near the bottom of the conduction band, while it is near the top of the valence base in the p-type extrinsic semiconductor.

In intrinsic semiconductors, there is a small gap between the valance band and the conduction. On the other hand, the extrinsic semiconductor has a larger energy gap than the intrinsic semiconductor. The conduction of intrinsic semiconductors depends on the temperature, while the conduction of extrinsic semiconductors depends on the temperature and concentration of the doped impurity.

Examples of intrinsic semiconductors are Si and Ge etc. On the other hand, examples of extrinsic semiconductors are GaAs, GaP, etc.

Comparison chart

What is intrinsic semiconductor ?

The word “intrinsic” means “pure.” So the intrinsic semiconductor is a pure semiconductor without any doping element or impurity present in it. This type of semiconductor is also recognized as type io semiconductor or undoped semiconductor. That is why the number of charge carriers is based on the properties of the material but not on the number of impurities.

In intrinsic semiconductors, the electrons present in the conduction band and the holes present in the valence band are equal in number. Here holes are denoted p and electrons are denoted n, so in an intrinsic semiconductor n = p. In this type of semiconductors, the electrical conductivity depends on the crystallographic defects or even on the electronic excitation.

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

In the periodic table, group IV elements form intrinsic semiconductors. However, germanium and silicon play their part as intrinsic semiconductors, requiring 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 to its four neighboring atoms in crystalline form. These shared pairs of electrons form a valance bond or covalent bond.

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

Due to thermal energy, when an electron with charge –q is excited, it breaks from the bond causing a vacancy with charge +q there. This vacancy with positive electronic charge acts as a hole. These holes also act as 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 extrinsic semiconductor ?

An extrinsic semiconductor is a type of semiconductor that has been doped with any trace elements or impurities during its manufacture. The elements added in it are known as doping agents, and this process is known as doping agent. Therefore, the extrinsic semiconductor is also called a 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 exhibited by the material and the impurities added in it.

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

When doping a material, it must be kept in mind that the amount of impurity mixed into the material must not affect the lattice structure of the semiconductor. To get to this point, the size of the semiconductor atoms and the dopant must be equal. For example, silicon and germanium crystals mix with trivalents (3 valences) and pentavalents (5 valences) because they have the same crystal size.

Types

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

Key differences

1. A pure semiconductor without any doping elements present in it is known as an intrinsic semiconductor, while a semiconductor that has been doped with any trace elements or doping agents during its manufacture is known as an extrinsic semiconductor.
2. Intrinsic semiconductors are also known as type io semiconductors or undoped semiconductors. On the other hand, extrinsic semiconductor is also called doped semiconductor.
3. Intrinsic semiconductors have poor conductivity. On the contrary, extrinsic semiconductors have better conductivity due to the addition of impurities in them.
4. Intrinsic semiconductors are not divided into any type; On the other hand, extrinsic semiconductors are further divided into p-type semiconductors and n-type semiconductors.
5. In intrinsic semiconductors, the center of the forbidden energy gap has the Fermi energy level. On the other hand, in the n-type extrinsic semiconductor, the Fermi level is present near the bottom of the conduction band, while it is near the top of the valence base in p-type.
6. There is a small gap between the valance band and the conduction in an intrinsic semiconductor, while the extrinsic semiconductor has a higher energy gap.
7. The conduction of intrinsic semiconductors depends on temperature; on the other hand, the conduction of the extrinsic semiconductor depends on the temperature and concentration of the doped impurity.
8. In an intrinsic semiconductor, the electrons present in the conduction band and the holes present in the valence band are equal in number, while the 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.
9. Examples of intrinsic semiconductors are Si and Ge etc. On the other hand, examples of extrinsic semiconductors are GaAs, GaP, etc.

Final Thought

The above discussion summarizes that the intrinsic semiconductor is a type of pure semiconductor without any added impurities, for example silicon or germanium etc. On the other hand, extrinsic semiconductor is a kind of impure semiconductor with the doping agents or impurities added in, for example GaP or GaAs etc.