Which is the Semiconductor Material?
A material is said to be a semiconductor material if its conductivity is greater than that of an insulator and less than that of a conductor. That means the conductivity of the semiconductor lies between that of the insulator and the conductor. We can define the semiconductor material based on the energy band gap also.
The energy band gap is nothing but the difference between the lowest level of the conduction band and the highest level of the valence band. A material is said to be a semiconductor material if its energy bandgap is greater than that of a conductor and less than that of an insulator. That means the energy band gap of semiconductors lies between that of conductor and insulator. You can easily understand this one from the following diagram.
Types of Semiconductor Material
Now, you are going to know how many types of semiconductor materials are available. We can classify the semiconductors mainly into two types based on the level of purity. Now, let’s discuss the following two types of semiconductors one by one.
- Intrinsic Semiconductor
- Extrinsic Semiconductor
Intrinsic Semiconductor
Intrinsic semiconductors are also called undoped semiconductors since there are no impurities. In intrinsic semiconductors, the number of electrons and holes are the same. Due to this, the conductivity is poor in this semiconductor.
Silicon (Si) and Germanium (Ge) are examples of intrinsic semiconductors. The 4A group elements have the number of valence electrons as 4. If the total number of valence electrons is 8, then the crystal will become stable. By using covalent bonds, each Silicon (Si) atom can share one electron with four other Silicon (Si) atoms. The Silicon (Si) crystal lattice structure is shown in the below figure.
Extrinsic Semiconductor
If we add the impurities to the intrinsic semiconductor for improving the conductivity, then that material is called an extrinsic semiconductor. The process of adding impurities to the intrinsic semiconductor is known as doping. 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 the following two types based on most charge carriers.
- n-type Semiconductor: By doping 5A group elements (N, P, As, Sb, Bi) to the intrinsic semiconductor, then electrons will become majority charge carriers. Hence, this material is called an n-type semiconductor. The following figure illustrates the doping of Phosphorus to Silicon (Si) lattice.
- p-type Semiconductor: By doping 3A group elements (B, Al, Ga, In, Tl) to the intrinsic semiconductor, the holes will become majority charge carriers. Hence, this material is called a p-type semiconductor. The following figure illustrates the doping of Boron to Silicon (Si) lattice.
Applications of Semiconductor Materials
In most electronic devices and in Integrated Circuits, we use semiconductor materials. Among these, the most commonly used semiconductor material is silicon (Si). For optical devices and very high-speed devices, we use semiconductors like Gallium Arsenide (GaAs) and related compounds.
If we use semiconductor material in an electronic device, then it is known as a semiconductor device. Examples of semiconductor devices are Diodes (p-n junction, Zener, Tunnel, Varactor, LED, Laser & photodiodes), Transistors (BJT, JFET & MOSFET) and Integrated Circuits (Analog ICs & Digital ICs).
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