What are Semiconductors?
It is defined as the material that shows both the properties of the conductor and the insulator in different conditions. The conductivity of a semiconductor lies between the conductor and the insulator. Some examples of elementary semiconductors are silicon (Si) and germanium (Ge).
Energy Band Theory
Based on Pauli’s exclusion principle, the energy of an electron is definite in a single isolated atom, but after the formation of a molecule or crystal, the energy of an electron is not fixed but varies in some range, which is called the energy band. There are two important bands: The valence band and the Conduction band, respectively.
- Valence band: It represents the energy of bonded electrons, which are present in the valence band and do not take part in conduction.
- Conduction band: It represents the energy of free electrons, which are present in the conduction band and take part in conduction.
- Forbidden energy gap: It is defined as the energy gap between the valence and conduction band, and it is known as forbidden because no electron is present inside this energy gap. It is represented as ΔEg.
Classification of solids based on energy band theory:
Extrinsic Semiconductor
As we all know, based on conductivity, we divide the material into three categories: Conductor, Semiconductor, and Insulator. In which the conductivity of the conductor is highest, insulators have the lowest conductivity, and semiconductors have intermediate conductivity. The reason behind this is the number of free electrons present in the crystal of each material. If we talk about the conductivity of semiconductors, two different types of semiconductors are classified based on the number of electrons and holes present in the crystal: Intrinsic and Extrinsic semiconductors. In this article, we will discuss these semiconductors, especially extrinsic semiconductors, their properties, formation, needs, and various applications.
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