Types of Semiconductor

What is Semiconductor?

A material is said to be a semiconductor if its conductivity is greater than that of the insulator and less than that of the conductor. That means the conductivity of the semiconductor lies between that of the insulator and the conductor. We can define the semiconductor based on the energy band gap also.

The energy band gap is the difference between the conduction band's lowest level and the valence band's highest level. A material is said to be a semiconductor if its energy bandgap is greater than a conductor's and less than the insulators. That means the energy bandgap of the semiconductor lies between that of the conductor and insulator.

What are the Types of Semiconductors?

Now, you will know how many types of semiconductors are available. We can classify the semiconductors mainly into two types based on the purity level. Now, let’s discuss the following two types of semiconductors.

• Intrinsic Semiconductor
• Extrinsic Semiconductor

Let us explore each semiconductor in detail in the coming sections.

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Intrinsic Type Semiconductor

Intrinsic semiconductors are also called undoped semiconductors since there are no impurities. Examples of intrinsic semiconductors are Silicon (Si) and Germanium (Ge). A semiconductor is said to be an intrinsic semiconductor if it has the following properties or characteristics.

• The number of electrons and holes are the same.
• Conductivity is poor.
• Chemically very pure. i.e., there are no impurities.

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Extrinsic Type Semiconductor

We will add the impurities from the external to the intrinsic semiconductor to improve the conductivity. Then that material is called an extrinsic semiconductor. Doping is nothing but the process of adding impurities to the intrinsic semiconductor. Due to doping, the number of electrons and holes will differ in this material.

Electrons are called negative charge carriers, whereas holes are called positive charge carriers. The absence of electrons is nothing but holes. We can classify these semiconductors into two types based on most charge carriers. Now, let’s discuss the following two types of extrinsic semiconductors.

• n-type Semiconductor
• p-type Semiconductor

The n-type Semiconductor

If we want to improve the conductivity due to electrons, we must be doping 5A group elements to the intrinsic semiconductor. Then that material is called an n-type semiconductor. Nitrogen (N), Phosphorus (P), Arsenic (As), Antimony (Sb), and Bismuth (Bi) are the 5A group elements.

When we dope a 5A group element with an intrinsic semiconductor of the 4A group, then four electrons of each element will make covalent bonds. One electron of the 5A group element is free. In this way, if we do more doping, the number of free electrons will increase. That’s why this material is called an n-type semiconductor. Here, electrons are the majority charge carriers.

The p-type Semiconductor

If we want to improve the conductivity due to holes, we must be doping 3A group elements to the intrinsic semiconductor. Then that material is called a p-type semiconductor. Boron (B), Aluminium (Al), Gallium (Ga), Indium (In), and Thallium (Tl) are the 3A group elements.

When we doping the 3A group element with the intrinsic semiconductor of the 4A group, then three electrons of each element will make covalent bonds. Here, there is a shortage of one electron because of the 3A group element. The absence of electrons is nothing but holes. In this way, if we do more doping, the number of holes will increase. That’s why this material is called a p-type semiconductor. Here, holes are the majority of charge carriers.

Energy Bands in Different Types of Semiconductors

The energy bands and respective positions of charge carriers define the conductivity of semiconductor devices. The charge carriers can be moved either by disturbing the material's thermal equilibrium or doping, which converts the material to extrinsic.

Intrinsic Semiconductors

An intrinsic semiconductor will have four electrons in the valence band and no electrons in the conduction band. These carriers can be shifted to the conduction band by disturbing the thermal equilibrium. Still, due to the fundamental property of material, they will return to their original state by letting out that energy either in the form of heat or photons.

Extrinsic Semiconductors

In the case of extrinsic semiconductors, that is, after doping, there will be 1 electron added in the conduction band for n-type, and 1 hole will appear in the valence band for p-type extrinsic semiconductor.