If you do not have any idea that What is Semiconductor, then you have to read this article. In this article, Poly Notes Hub shares with you all about the Semiconductor and Its Types.
What is Semiconductor?
A semiconductor is a substance that has a resistivity (10^-4 to 0.5 Ohm-m) in between conductors and insulators e.g. Germanium, Silicon, Selenium, Carbon, etc.
Properties of Semiconductor
- The resistivity of a semiconductor is less than an insulator but more than a conductor.
- Semiconductors have negative temperature co-efficient of resistance the resistance of a semiconductor decreases with the increase in temperature and vice-versa. For example, germanium is an insulator at low temperatures but it becomes a good conductor at high temperatures.
- When a suitable metallic impurity is added to a semiconductor, it’s current conducting properties change appreciably. This property is most important and is discussed later in detail.
What is Crystal?
A substance in which the atoms or molecules are arranged in an orderly pattern is known as a crystal. All semiconductors have crystalline structure. Semiconductors like Germanium, Silicon, and Carbon has crystalline structure.
Commonly Used Semiconductor
There are many semiconductors available, but very few of them have a practical application in electronics. The two most frequently used materials are Germanium and Silicon. It is because the energy required to break their covalent bonds is very small; being about 0.7 eV for Germanium and about 1.1eV for Silicon. Therefore, we shall discuss these two semiconductors in detail.
Germanium
Germanium has become the model substance among Semiconductors; the main reason being that it can be purified relatively well and crystallized easily. Germanium is an earth element and was discovered in 1886. It is recovered from the Ash of certain coals or the flue dust of zinc smelters. Generally, recovered germanium is in the form of germanium dioxide powder which is then reduced to pure germanium.
The atomic number of Germanium is 32. Therefore is has 32 protons and 32 electrons. Two electrons are in the first orbit, eight electrons in the second, eighteen electrons in the third, and four electrons are in the outer or valance orbit. So, it is cleared that Germanium atom has four valance electrons so, it is a tetravalent element. Below shows the atomic structure of Germanium:
Silicon
Silicon is an element is most of the common rocks. Sand is silicon dioxide. The silicon compounds are chemically reduced to silicon which is 100% pure for use as a semiconductor.
The atomic number of Silicon is 14. Therefore it has 14 protons and 14 electrons. Two electrons are in the first orbit, eight electrons in the second, and four electrons are in the outer or valance orbit. So, it is clear that the Silicon atom has four valance electrons so, it is a tetravalent element. Below is the atomic structure of Silicon:
Types of Semiconductor
There are basically two types of Semiconductor
- Intrinsic Semiconductor
- Extrinsic Semiconductor
Intrinsic Semiconductor
A semiconductor is an extremely pure form known as an intrinsic Semiconductor.
In an intrinsic Semiconductor, even at room temperature, hole-electron pairs are created. When an electric field is applied across an intrinsic Semiconductor, the current conduction takes place by two processes, namely; by free electrons and holes as shown in the Figure. The free electrons are produced due to the breaking up of some covalent bonds by thermal energy. At the same time, holes are created in the covalent bonds. Under the influence of an electric field, conduction through the semiconductor is by both free electrons and holes.
Therefore, the total current inside the semiconductor is the sum of currents due to free electrons and holes.
Extrinsic Semiconductor
The intrinsic Semiconductor has little current condition capability at room temperature. To be useful in electronic devices, the pure semiconductor must be altered to significantly increase its conducting properties. This is achieved by adding a small amount of suitable impurity to a semiconductor. It is called impurity or extrinsic Semiconductor. This process of adding impurities to a semiconductor is known as doping. The amount and type of such Impurities have to be closely controlled during the preparation of extrinsic semiconductors. Generally, for 10⁸atoms of semiconductor, one impurity atom is added.
The purpose of adding impurity is to increase the number of free electrons or holes in the semiconductor crystal. Depending upon the types of impurity added, this type of semiconductor is classified into two categories:
- P-Types Semiconductor
- N-Type Semiconductor
To know more about P-Type and N-Type semiconductors. Click Here.
MCQs
Conclusion | Diploma Engineering Notes | Poly Notes Hub
In this article, we discuss What is semiconductors and their types. Semiconductors are used in different kinds of fields like Chip making, mobile memory, computer memory, and so on.
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