Sunday Emmanuel

@sundayemmanuel · 25 Nov 2021

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What is semiconductor

Semiconductors are a group of materials having electrical conductivity intermediate between metal and insulators. The conductivity of these materials can be varied over orders of magnitude by changes in temperature, optical excitation, and impurity content. Semiconductor materials have a narrow forbidden gap between the valence and conduction band; the energy gap is of order KT. 0k, all the electrons are in the valence band and the material is then an insulator. At room temperature, however, some of the valence electrons can acquire sufficient thermal energy which they used to move into the conduction band where they become free electrons. In place of liberated electrons, holes are created in the valence band. The conduction of electricity in a semiconductor is due to the movement of free electrons and holes.

Metals are excellent conductors of electricity.in metals, the conduction and valence band overlap such that at all temperatures above absolute zero, electrons are always readily available in the conduction band. Also, the valence electrons are weakly Bond to the parent atoms in metals such that a slight potential difference across a conductor causes the free electrons to constitute an electric current.


Conduction in the intrinsic semiconductor material

In an intrinsic or pure semiconductor at 0k, all the valence electrons are tightly bound to their parent atoms and the semiconductor behaves as an insulator. As the temperature is increased, some of the valence electrons can break their covalent bonds and move from the valence band into the conduction band where they become free electrons. An electron moving from the valence band into the conduction band leaves a free hole in the valence band. a free charge (electron or hole) is not tightly bound to any atom and can move freely through the material.

Conduction in an extrinsic semiconductor

The number of free electrons and holes that are thermally generated in intrinsic or pure semiconductor crystals is very small at room temperature. The number of charge carriers can be considerably increased by purposely introducing impurities called dopants into the pure semiconductor crystals. The process is called doping. By doping, a crystal can be altered such that it has a predominance of either electrons or holes. Thus, there are two types of doped semiconductors:

N-type semiconductor

Certain elements such as phosphorus, arsenic, and antimony are pentavalent i.e. each atom has 5 valence electrons. An n-type semiconductor is formed when an intrinsic material is doped with an atom of a pentavalent element. The pentavalent atom shares four of its five valence electrons with adjacent atoms but the fifth electron is not tightly bound to its parent's atom and is free to facilitate the flow of current through the material. In this type of semiconductor, the number of electrons is more than the number of holes. That is, an electron at the majority charge carrier while holes are the minority charge carrier

P-type semiconductor

Materials such as indium, gallium, boron, and aluminum are trivalent i.e. each atom has only three valence electrons. A p-type semiconductor is formed when an intrinsic material is doped with atoms of a trivalent element called acceptor atoms. Each trivalent atom forms three covalent bonds with three neighboring silicon atoms thereby creating a hole where the fourth Bond is supposed to be. In a p-type material, holes are the majority charge carrier why the few thermally generated electrons are minority charge carriers.@Henkjan de Krijger #whatissemiconductor #conductionintheintrinsicsemiconductormaterial #ntypesemiconductor  #ptypesemiconductor#Conductioninanextrinsicsemiconductor